Advances in Chiral Pincer Complexes: Insights and Applications in Catalytic Asymmetric Reactions

Chiral pincer complexes, characterized by their rigid tridentate coordination framework, have emerged as powerful catalysts in asymmetric synthesis. This review provides a comprehensive overview of recent advancements in the development of chiral pincer-type ligands and their corresponding transition metal complexes. We highlight the latest progress in their application across a range of catalytic asymmetric reactions, including the (transfer) hydrogenation of polar and non-polar bonds, hydrophosphination, alkynylation, Friedel-Crafts reactions, enantioselective reductive cyclization of alkynyl-tethered cyclohexadienones, enantioselective hydrosilylation, as well as Aza-Morita-Baylis-Hillman reactions. The structural rigidity and tunability of chiral pincer complexes enable precise control over stereoselectivity, resulting in high enantioselectivity and efficiency in complex molecular transformations. As the field advances, innovations in ligand design and the exploration of new metal centers are expected to expand the scope and utility of these catalysts, bearing significant implications for the synthesis of enantioenriched compounds in pharmaceuticals, materials science, and beyond.

Enantioselective Reductive Cyclization of Alkynyl-Tethered Cyclohexadienones Catalyzed by Rhodium Complexes

Although various types of asymmetric cyclization reactions of 1,6-enynes have been established, simple asymmetric reductive cyclization remains underdeveloped. In this study, the enantioselective reductive cyclization of alkynyl-tethered cyclohexadienones (1,6-enynes) has been developed via a chiral pincer rhodium catalyst, affording cis-hydrobenzofurans and cis-hydroindoles with high enantioselectivities (90-99% ee). Furthermore, several synthetic applications and preliminary inhibitory activity studies against SARS-CoV-2 3CLpro are presented.

Deciphering substitution effects on reductive hydroalkoxylation of alkynyl aminols for stereoselective synthesis of morpholines and 1,4-oxazepanes: total synthesis of tridemorph and fenpropimorph

Acid catalysed reductive etherification of N-propargyl amino alcohols for the stereoselective synthesis of cis-2,5/2,6-disubstituted morpholines and cis-2,6/2,7-disubstituted oxazepanes has been developed. Mechanistic studies revealed that terminal alkynols gave morpholines via a 6-exo-dig hydroalkoxylation-isomerization-reduction cascade. Interestingly, an alkyne hydration-cyclization-reduction sequence is found to be involved in the formation of oxazepanes from alkyl substituted internal alkynols. The strategy was used as a key step in the total synthesis of fungicides tridemorph and fenpropimorph.

Pd-Catalyzed Enantioselective Desymmetrizing 1,7-Enyne Cycloisomerization of Alkyne-Tethered Cyclopentenes

An enantioselective Pd-catalyzed intramolecular desymmetrizing cycloisomerization of N-(cyclopent-3-en-1-yl)propiolamides has been developed by employing a new chiral phosphoramidite ligand. A series of structurally unique bridged azabicycles are achieved in moderate to excellent yields with good E/Z selectivity and high enantioselectivity. Synthetic transformations are conducted to demonstrate the practical utility of this reaction.

Enantioselective Synthesis of Bicyclo[3.2.1]octadienes via Palladium-Catalyzed Intramolecular Alkene-Alkyne Coupling Reaction

Bicyclo[3.2.1]octadiene compounds and derivatives exist in a number of natural products and bioactive compounds. Nevertheless, catalytic enantioselective protocols for the synthesis of these skeletons have not been disclosed. Herein we reported a palladium-catalyzed asymmetric intramolecular alkene-alkyne coupling of alkyne-tethered cyclopentenes, affording a library of enantionenriched bicyclo[3.2.1]octadienes in excellent yields and enantioselectivities (mostly >99 % ee). Moreover, the products could undergo an unusual iodination-induced 1,2-acyl migration, forming iodinated bicyclo[3.2.1]octadienes with three vicinal stereocenters. The enone and isolated olefin motifs embedded in the products provide useful handles for downstream elaboration.

Cobalt-Catalyzed Chemo- and Stereoselective Arylative Carbocyclization of 1,6-Allenynes

Different from the well-investigated enynes, transition-metal-catalyzed carbocyclization reactions of allenynes are more attractive as a result of the unique structure and versatile reactivity of allenes. Herein, we report the first cobalt-catalyzed highly chemo- and stereoselective arylative carbocyclization of 1,6-allenynes with arylboronic acids, affording five-membered carbocycles and heterocycles with moderate to high yields, broad substrate scope, and wide functional group compatibility. Moreover, several mechanistic experiments were conducted to gain insight into the reaction process.

Cobalt-catalyzed enantioselective intramolecular reductive cyclization via electrochemistry

Transition-metal catalyzed asymmetric cyclization of 1,6-enynes has emerged as a powerful method for the construction of carbocycles and heterocycles. However, very rare examples worked under electrochemical conditions. We report herein a Co-catalyzed enantioselective intramolecular reductive coupling of enynes via electrochemistry using H₂O as hydride source. The products were obtained in good yields with high regio- and enantioselectivities. It represents the rare progress on the cobalt-catalyzed enantioselective transformation via electrochemistry with a general substrate scope. DFT studies explored the possible reaction pathways and revealed that the oxidative cyclization of enynes by LCo(I) is more favorable than oxidative addition of H₂O or other pathways.

Gold-Catalyzed Cyclization/Hydroboration of 1,6-Enynes: Synthesis of Bicyclo[3.1.0]hexane Boranes

The gold-catalyzed cyclization/hydroboration of 1,6-enynes offers facile, versatile, and atom-economical one-step access to bicyclo[3.1.0]hexane boranes. This new protocol proceeds in moderate to good yields under mild conditions. Different from bicyclo[3.1.0]hexane borates, these products are stable in air and during chromatography. Moreover, the borane moiety of the products can readily undergo a diverse array of transformations. The kinetic isotope effect experiment indicates that the hydrogen-transfer step is a fast process, which is not involved in the rate-limiting step.

Synthesis of 1H-Isochromenes and 1,2-Dihydroisoquinolines by Indium(III)-Catalyzed Cycloisomerization of ortho-(Alkynyl)benzyl Derivatives

1H-Isochromenes and 1,2-dihydroisoquinolines are synthesized by regioselective indium(III)-catalyzed intramolecular hydrofunctionalization of o-(alkynyl)benzyl derivatives. The reaction with o-(alkynyl)benzyl alcohols and amines proceeds using indium triiodide (5–10 mol%) in toluene at 80–100 °C via regioselective 6-endo-dig intramolecular alkyne hydroalkoxylation or hydroamination in good yields. Alternatively, the cycloisomerization reaction of o-(alkynyl)benzaldehydes and imine derivatives using InI3 (5 mol%) and the Hantzsch ester (120 mol%) takes place, under milder reaction conditions, to give a variety of functionalized 1H-isochromenes and 1,2-dihydroisoquinolines through a domino cycloisomerization/reduction approach.

Iron-Catalyzed Cycloisomerization and C-C Bond Activation to Access Non-canonical Tricyclic Cyclobutanes

Cycloisomerizations are powerful skeletal rearrangements that allow the construction of complex molecular architectures in an atom-economic way. We present here an unusual type of cyclopropyl enyne cycloisomerization that couples the process of a cycloisomerization with the activation of a C-C bond in cyclopropanes. A set of substituted non-canonical tricyclic cyclobutanes were synthesized under mild conditions using [(Ph3 P)2 Fe(CO)(NO)]BF4 as catalyst in good to excellent yields with high levels of stereocontrol.

Ruthenium-Catalyzed Geminal Hydroborative Cyclization of Enynes

Disclosed here is the first geminal (gem-) hydroborative cyclization of enynes. Different from known hydroborative cyclizations, this process adds hydrogen and boron to the same position, leading to a new reaction mode. With [Cp*RuCl]₄ as catalyst, a range of gem-hydroborated bicyclic products bearing a cyclopropane unit could be rapidly assembled from simple enyne substrates. Control experiments and density functional theory (DFT) calculations provided important insights into the reaction mechanism. Notably, two major competing pathways may operate with substrate-dependence. 1,6-Enynes favor initial oxidative cyclometalation to form a ruthenacyclopentene intermediate prior to engaging hydroborane, while other enynes (e.g., 1,7-enynes) that lack strong propensity toward cyclization prefer initial alkyne gem-(H,B)-addition to form an α-boryl ruthenium carbene followed by intramolecular olefin cyclopropanation. This process also represents the first ruthenium-catalyzed enyne hydroborative cyclization.

Diametric calix[6]arene gold(I) catalysts for intramolecular cyclopropanations of 1,6-dienynes

We report a solid-state structural investigation of diametric calix[6]arene-based phosphine gold(I) cavitands which are characterised by two specific, different 1,2,3-alternate conformations in solution and in the solid state. The effect of the specific orientation of phosphines, with respect to macrocycles, was studied in intramolecular cyclopropanation of 1,6-dienynes. The general applicability of these catalysts was disclosed, delivering a family of polycycles with high yields and functional group tolerance.

Set of Cytochrome P450s Cooperatively Catalyzes the Synthesis of a Highly Oxidized and Rearranged Diterpene-Class Sordarinane Architecture

Cytochrome P450s are one of the most versatile oxidases that catalyze significant and unique chemical transformations for the construction of complex structural frameworks during natural product biosynthesis. Here, we discovered a set of P450s, including SdnB, SdnH, SdnF, and SdnE, that cooperatively catalyzes the reshaping of the inert cycloaraneosene framework to form a highly oxidized and rearranged sordarinane architecture. Among them, SdnB is confirmed to be the first P450 (or oxidase) that cleaves the C-C bond of the epoxy residue to yield formyl groups in pairs. SdnF selectively oxidizes one generated formyl group to a carboxyl group and accelerates the final Diels-Alder cyclization to furnish the sordarinane architecture. Our work greatly enriches the enzyme functions of the P450 superfamily, supplies the missing skills of the P450 synthetic toolbox, and supports them as biocatalysts in further applications toward the synthesis of new chemical entities.

Synthesis of chiral polycyclic N-heterocycles via gold(I)-catalyzed 1,6-enyne cyclization/intramolecular nucleophilic addition

Cycloisomerization of N-tethered indole- and dihydropyrrole-arylpropargyl substrates into complex polycycles was investigated by using gold(I) catalysis. Enantioselectivities up to 93% ee were obtained in the asymmetric version of this process. DFT calculations rationalized the reactivity observed for the formation of such complex molecular frameworks.

Skipped dienes in natural product synthesis

Covering: 2000-2020The 1,4-diene motif, also known as a skipped diene, is widespread across various classes of natural products including alkaloids, fatty acids, terpenoids, and polyketides as part of either the finalized structure or a biosynthetic intermediate. The prevalence of this nonconjugated diene system in nature has resulted in numerous encounters in the total synthesis literature. However, skipped dienes have not been extensively reviewed, which could be attributed to overshadowing by the more recognized 1,3-diene system. In this review, we aim to highlight the relevance of skipped dienes in natural products through the lens of total synthesis. Subjects that will be covered include nomenclature, structural properties, prevalence in natural products, synthetic strategies and the future direction of the field.

Rhodium-catalyzed intermolecular enantioselective Alder-ene type reaction of cyclopentenes with silylacetylenes

The Alder-ene type reaction between alkenes and alkynes provides an efficient and atom-economic method for the construction of C-C bond, which has been widely employed in the synthesis of natural products and other functional molecules. The intramolecular enantioselective Alder-ene cycloisomerization reactions of 1,n-enynes have been extensively investigated. However, the intermolecular asymmetric version has not been reported, and remains a challenging task. Herein, we describe a rhodium-catalyzed intermolecular enantioselective Alder-ene type reaction of cyclopentenes with silylacetylenes. A variety of chiral (E)-vinylsilane tethered cyclopentenes bearing one quaternary carbon and one tertiary carbon stereocenters are achieved in high yields and enantioselectivities. The reaction undergoes carbonyl-directed migratory insertion, β-H elimination and desymmetrization of prochiral cyclopentenes processes.

Inter/Intramolecular Cascade of 1,6-Enynes Catalyzed by All-Metal Aromatic Tripalladium Complexes and Carboxylic Acids

Trinuclear all-metal aromatic clusters are an original class of molecules with a cyclic and planar metal core. Characterized by peculiar metal-metal delocalized bonds, they represent a new frontier in transition-metal catalysis. We report a study on C-C-forming reactions of polyunsaturated substrates catalyzed by trinuclear all-metal aromatic palladium clusters. The synthesis of two new families of tricyclic compounds was obtained with a broad functional group tolerance under mild reaction conditions. A peculiar regio- and diastereoselectivity characterized the method, demonstrating that trinuclear palladium complexes are complementary to their popular mononuclear peers. Furthermore, preliminary studies on the mechanism of these polycyclization reactions revealed unique features of the homogeneous catalytic system.

Triaminocyclopentadienyl Ruthenium Complexes - New Catalysts for Cascade Conversions of Propargyl Alcohols

Various triaminocyclopentadienyl ruthenium complexes have been synthesized from Ru₃ (CO)₁₂ . The new complexes were tested for their ability to catalyze cascade conversions of propargyl alcohols. Their associated catalytic activities complement the activities of known diaminocyclopentadienone ruthenium complexes. In particular, the substrate scope of catalytic cycloadditions with 3-ketolactones or phloroglucinol derivatives is extended to terpenoid-derived propargyl alcohols containing an internal alkyne moiety. A wide range of cyclic terpenoid and phloroglucinol adducts are obtained by complementary application of both types of catalysts.

Enantioselective "organocatalysis in disguise" by the ligand sphere of chiral metal-templated complexes

Asymmetric catalysis holds a prominent position among the important developments in chemistry during the 20th century. This was acknowledged by the 2001 Nobel Prize in chemistry awarded to Knowles, Noyori, and Sharpless for their development of chiral metal catalysts for organic transformations. The key feature of the catalysts was the crucial role of the chiral ligand and the nature of the metal ions, which promoted the catalytic conversions of the substrates via direct coordination. Subsequently the development of asymmetric organic catalysis opened new avenues to the synthesis of enantiopure compounds, avoiding any use of metal ions. Recently, an alternative approach to asymmetric catalysis emerged that relied on the catalytic functions of the ligands themselves boosted by coordination to metal ions. In other words, in these hybrid chiral catalysts the substrates are activated not by the metal ions but by the ligands. The activation and enantioselective control occurred via well-orchestrated and custom-tailored non-covalent interactions of the substrates with the ligand sphere of chiral metal complexes. In these metal-templated catalysts, the metal served either as a template (a purely structural role), or it constituted the exclusive source of chirality (metal-centred chirality due to the spatial arrangement of achiral or chiral bi-/tridentate ligands around an octahedral metal centre), and/or it increased the Brønsted acidity of the ligands. Although the field is still in its infancy, it represents an inspiring combination of both metal and organic catalysis and holds major unexplored potential to push the frontiers of asymmetric catalysis. Here we present an overview of this emerging field discussing the principles, applications and perspectives on the catalytic use of chiral metal complexes that operate as "organocatalysts in disguise". It has been demonstrated that these chiral metal complexes are efficient and provide high stereoselective control in asymmetric hydrogen bonding catalysis, phase-transfer catalysis, Brønsted acid/base catalysis, enamine catalysis, nucleophilic catalysis, and photocatalysis as well as bifunctional catalysis. Also, many of the catalysts have been identified as highly effective catalysts at remarkably low catalyst loadings. These hybrid systems offer many opportunities in the synthesis of chiral compounds and represent promising alternatives to metal-based and organocatalytic asymmetric transformations.

Metabolic engineering strategies for sesquiterpene production in microorganism

Sesquiterpenes are a large variety of terpene natural products, widely existing in plants, fungi, marine organisms, insects, and microbes. Value-added sesquiterpenes are extensively used in industries such as: food, drugs, fragrances, and fuels. With an increase in market demands and the price of sesquiterpenes, the biosynthesis of sesquiterpenes by microbial fermentation methods from renewable feedstocks is acquiring increasing attention. Synthetic biology provides robust tools of sesquiterpene production in microorganisms. This review presents a summary of metabolic engineering strategies on the hosts and pathway engineering for sesquiterpene production. Advances in synthetic biology provide new strategies on the creation of desired hosts for sesquiterpene production. Especially, metabolic engineering strategies for the production of sesquiterpenes such as: amorphadiene, farnesene, bisabolene, and caryophyllene are emphasized in: Escherichia coli, Saccharomyces cerevisiae, and other microorganisms. Challenges and future perspectives of the bioprocess for translating sesquiterpene production into practical industrial work are also discussed.

Characterization and Utilization of the Elusive α,β-Unsaturated N-Tosyliminium: the Synthesis of Highly Functionalizable Skipped Halo Enynes

A formal haloalkynylation of allenamides has been described for the synthesis of highly stereo- and regioselective skipped halo enynes. Exclusive γ-regioselectivity is achieved through the intermediacy of a conjugated N-tosyliminium intermediate-direct evidence for the formation of which was validated by NMR and HRMS. Quantum mechanical computations reveal that the reactive intermediate geometry is key to controlling the 1,2- or 1,4-regioselectivity of alkyne interception. Divergent access to elusive unsaturated systems has also been reported.

On the Structure of Intermediates in Enyne Gold(I)-Catalyzed Cyclizations: Formation of trans-Fused Bicyclo[5.1.0]octanes as a Case Study

The nature of cyclopropyl gold(I) carbene-type intermediates has been reexamined as part of a mechanistic study on the formation of cis- or trans-fused bicyclo[5.1.0]octanes in a gold(I)-catalyzed cascade reaction. Benchmark of DFT methods together with QTAIM theory and NBO analysis confirms the formation of distinct intermediates with carbenic or carbocationic structures in the cycloisomerizations of enynes.

Gold-Catalyzed Synthesis of Small Rings

Three- and four-membered rings, widespread motifs in nature and medicinal chemistry, have fascinated chemists ever since their discovery. However, due to energetic considerations, small rings are often difficult to assemble. In this regard, homogeneous gold catalysis has emerged as a powerful tool to construct these highly strained carbocycles. This review aims to provide a comprehensive summary of all the major advances and discoveries made in the gold-catalyzed synthesis of cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, and their corresponding heterocyclic or heterosubstituted analogs.

Palladium-Catalyzed Intramolecular Alder-Ene Type Cycloisomerization Reactions

An overview of the recent literature on palladium-catalyzed intramolecular Alder-ene (IMAE) reaction of a variety of 1,n-unsaturated systems is presented. The reaction which was first reported by Trost and Lautens provided an efficient alternative to the thermal or Lewis acid catalyzed cycloisomerizations involving ene-type reaction. The IMAE cyclization of enynes and dienes has emerged as an important area and found significant applications in building up of complex molecular architectures and in the synthesis of several bioactive natural products. Since highly impactful reviews on this subject have covered the literature till 2015, this article focuses on summarizing the works subsequent to 2015.

Acetylene as a Dicarbene Equivalent for Gold(I) Catalysis: Total Synthesis of Waitziacuminone in One Step

The gold(I)-catalyzed reaction of acetylene gas with alkenes leads to (Z,Z)-1,4-disubstituted 1,3-butadienes and biscyclopropanes depending on the donor ligand on gold(I). Acetylene was generated in situ from calcium carbide and water in a user-friendly procedure. Reaction of acetylene with 1,5-dienes gives rise stereoselectively to tricyclo[5.1.0.02,4 ]octanes. This novel double cyclopropanation has been applied to the one step total synthesis of the natural product waitziacuminone from acetylene and geranyl acetone.

Triflic Acid-Catalyzed Cycloisomerization of 1,6-Enynes: Facile Access to Carbo- and Azaheterocycles

A new and efficient strategy for enynes cyclization catalyzed by triflic acid has been described. Various valuable carbocycle-fused and heterocycle-fused ketones were easily accessed by the formation of new C-C and C-O bond under benign reaction conditions. This protocol also provides another opportunity to construct polycyclic single-nitrogen ketones via a cation-induced cascade cyclization of polyenynes. Furthermore, antiviral bioassays revealed that a few compounds exhibited good antiviral activity against tobacco mosaic virus at a concentration of 200 μg mL^-1.

Mechanistic Study on Gold-Catalyzed Cycloisomerization of Dienediynes Involving Aliphatic C-H Functionalization and Inspiration for Developing a New Strategy to Access Polycarbocycles

Previously, we developed a gold-catalyzed cycloisomerization of dienediynes to synthesize the fused 6,7,5-tricyclic compounds. This reaction involves aliphatic C-H functionalization under mild conditions with high regio- and diastereoselectivities. Herein, we present a combined density functional theory (DFT) and experimental study to understand its mechanism. The reaction starts with a 6-endo-dig cyclization to generate a cis-1-alkynyl-2-alkenylcyclopropane. Then, a Cope rearrangement takes place to give a seven-membered-ring allene intermediate, whose central carbon atom possesses vinyl cation character and thus is highly reactive toward aliphatic C-H insertion. After the C-H insertion, two successive [1,2]-hydride shifts then occur to give the tricyclic product and to complete the catalytic cycle. Notably, steric effect induced by the bulky ligand is found to be important for the diastereocontrol in the C-H insertion step. DFT calculations suggested that the malonate-tethered substrate utilized in our previous work may undergo an undesired 5-exo-dig cyclization under gold catalysis, which could be the reason why the desired fused 6,7,5-tricarbocyclic product was not generated. These mechanistic insights then guided us to design substrates with a shortened carbon tether in the present work to inhibit the exo-dig cyclization so that the tandem cyclopropanation/Cope rearrangement/C-H functionalization could occur to construct polycarbocycles containing a seven-membered ring. This prediction was supported by new experiments, providing a new strategy to access fused 5,7,5-tricyclic and 5,7,6,6-tetracyclic carbocycles. In addition, how the substituents affect the chemoselectivity was also investigated.

Stereodivergent routes in organic synthesis: carbohydrates, amino acids, alkaloids and terpenes

The natural occurrence of enantiomers and diastereomers is often encountered.

Recent progress in the synthesis of limonoids and limonoid-like natural products

Recent progress in syntheses of limonoids and limonoid-like natural products is reviewed. The current “state-of-art” advance on novel synthetic strategy are summarized and future outlook will be presented.

Ruthenium-catalysed cyclisation reactions of 1,11-dien-6-ynes leading to biindenes

1,1′-Biindenes were prepared from 1,2-bis(2-allylphenyl)ethynes via cycloisomerisation and tandem RCM reactions, both of which are catalysed by ruthenium.

Total Synthesis and Structural Revision of a Harziane Diterpenoid

The first total synthesis of nominal harziane diterpenoid 1 is disclosed, whose spectral characteristics did not match those of the reported natural product. Stereochemical analysis and subsequent synthesis of the epimeric tertiary alcohol led to reassignment of configuration of the natural product as shown for 2. At the heart of the synthesis is an enyne cycloisomerization that sets a key quaternary stereocenter within a cyclobutane with high diastereocontrol. The route features strategies for the synthesis of the highly congested 6-5-7-4 carbon skeleton characteristic of the caged harziane diterpenoids.

PtCl2-Catalyzed Cycloisomerization of 1,8-Enynes: Synthesis of Tetrahydropyridine Species

The cycloisomerization of 1,8-enynes in the presence of platinum(II) chloride was developed to generate bicyclic nitrogen-containing heterocycle species via 6- endo-dig cyclization and [3,3]-sigmatropic rearrangement in acceptable to good yields. The related control experiments and preliminary mechanistic studies indicate a plausible mechanism involving 1,6- endo-dig aminoplatination of the alkyne and allylic [3,3]-sigmatropic rearrangement with total inversion of the allylic moiety.

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

Gold is currently one of the most used metals in organometallic catalysis. The ability of gold to activate unsaturated groups in different modes, together with its tolerance to a wide range of functional groups and reaction conditions, turns gold-based complexes into efficient and highly sought after catalysts. Natural products and relevant compounds with biological and pharmaceutical activity are often characterized by complex molecular structures. (Cyclo)isomerization reactions are often a useful strategy for the generation of this molecular complexity from synthetically accessible reactants. In this review, we collect the most recent contributions in which gold(I)- and/or gold(III)-catalysts mediate intramolecular (cyclo)isomerization transformations of unsaturated species, which commonly feature allene or alkyne motifs, and organize them depending on the substrate and the reaction type.

A rhodium catalyzed cycloisomerization and tandem Diels-Alder reaction for facile access to diverse bicyclic and tricyclic heterocycles

A rhodium catalyzed cycloisomerization of 1,6-allenenes successfully prepared six-membered ring exocyclic 1,3-dienes. Further tandem Diels–Alder reaction with various dienophiles provided diverse bicyclic and tricyclic heterocycles. This methodology is characterised by complete atom and step economy, low catalyst loading, and excellent chemo-, regio-, and diastereoselectivity.

A regioselective distal cycloisomerization of 1,6-allenenes was successfully developed to afford six-membered ring exocyclic 1,3-dienes employing a rhodium/diphosphine catalyst system. Deuterium labelling experiments and DFT calculations were performed to provide insights into the reaction mechanism of this unprecedented transformation. In addition, one-pot tandem Diels–Alder reactions with various dienophiles could readily construct diverse bicyclic and tricyclic nitrogen heterocycles, which are ubiquitous core scaffolds for a variety of natural products and bioactives. High efficiency and exclusive chemo and regioselectivities for a broad substrate scope were achieved under mild conditions using a low catalyst loading of 0.5 mol%.