Regio- and stereocontrol elements in Rh(II)-catalyzed intramolecular C-H insertion of alpha-diazo-alpha-(phenylsulfonyl)acetamides

Sulfoxonium ylides: simple compounds with chameleonic reactivity

Sulfoxonium ylides, manageable compounds with an appealing safety profile, adapt to reaction partners like chameleons to their environment, resulting in a variety of useful, and sometimes surprising and unique, reactions.

Sodium Diisopropylamide-Mediated Dehydrohalogenations: Influence of Primary- and Secondary-Shell Solvation

Eliminations of alkyl halides by sodium diisopropylamide (NaDA) in tetrahydrofuran (THF)/hexane or THF/N,N-dimethylethylamine (DMEA) solutions are facile and complementary to analogous reactions of lithium diisopropylamide in THF. Rate studies show a dominance of monomer-based metalations and prevalent secondary-shell solvation effects overlaid on primary-shell effects. 1-Halooctanes exclusively undergo elimination rather than substitution. Rate and isotopic labeling studies on 1-bromooctane reveal an E2-like elimination pathway via trisolvated NaDA monomer. By contrast, 1-chlorooctane is eliminated via disolvated monomer through a carbenoid mechanism. exo-2-Norbornyl chloride and bromide are also eliminated via disolvated monomer; a syn E2 mechanism is inferred for these substrates. The cis- and trans-4-tert-butylcyclohexyl bromides show a preference for the elimination of the cis isomer (k_cis/ax/k_trans/eq = 10). Rate and isotopic labeling studies are consistent with a trans-diaxial E2 elimination via trisolvated monomer for the cis isomer and a carbenoid mechanism via disolvated monomer for the trans isomer. Vicinal haloethers show substrate-dependent reactivities, affording alkynes and enol ethers. trans-1-Bromo-2-methoxycyclohexane provides enol ether 1-methoxycyclohexene, while trans-1-bromo-2-methoxycyclooctane provides dimeric products consistent with fleeting cycloocta-1,2-diene (cyclic allene), which was fully characterized as two conformers.

Iridium-Catalyzed Enantioselective C(sp3)-H Amidation Controlled by Attractive Noncovalent Interactions

While remarkable progress has been made over the past decade, new design strategies for chiral catalysts in enantioselective C(sp³)-H functionalization reactions are still highly desirable. In particular, the ability to use attractive noncovalent interactions for rate acceleration and enantiocontrol would significantly expand the current arsenal for asymmetric metal catalysis. Herein, we report the development of a highly enantioselective Ir(III)-catalyzed intramolecular C(sp³)-H amidation reaction of dioxazolone substrates for synthesis of optically enriched γ-lactams using a newly designed α-amino-acid-based chiral ligand. This Ir-catalyzed reaction proceeds with excellent efficiency and with outstanding enantioselectivity for both activated and unactivated alkyl C(sp³)-H bonds under very mild conditions. It offers the first general route for asymmetric synthesis of γ-alkyl γ-lactams. Water was found to be a unique cosolvent to achieve excellent enantioselectivity for γ-aryl lactam production. Mechanistic studies revealed that the ligands form a well-defined groove-type chiral pocket around the Ir center. The hydrophobic effect of this pocket allows facile stereocontrolled binding of substrates in polar or aqueous media. Instead of capitalizing on steric repulsions as in the conventional approaches, this new Ir catalyst operates through an unprecedented enantiocontrol mechanism for intramolecular nitrenoid C-H insertion featuring multiple attractive noncovalent interactions.

Regio- and Enantioselective Intramolecular Amide Carbene Insertion into Primary C-H Bonds Using Ru(II)-Pheox Catalyst

We have established a method for the highly regio- and enantioselective functionalization of tert-butyl groups via intramolecular amide carbene insertion into C-H bonds, yielding γ-lactams with 91% ee in up to 99% yield. This reaction uses a ruthenium(II) phenyl oxazoline (Ru(II)-Pheox) complex. The catalytic intramolecular carbene transfer reaction to the primary C-H bond proceeds rapidly and selectively compared to that with secondary C-H, benzylic secondary C-H, tert-C-H, or sp²C-H bonds in the presence of 1 mol % Ru(II)-Pheox catalyst. This is the first example of a catalytic carbenoid insertion into an unactivated tert-butyl group with enantiocontrol at the carbenoid carbon.

Highly stereoselective intramolecular Buchner reaction of diazoacetamides catalyzed by a Ru(ii)–Pheox complex

This work reports the first efficient enantioselective intramolecular Buchner reaction of diazoacetamides.

Auxiliary ligand-aided tuning of aggregation of transition metal benzoates: isolation of four different types of coordination polymers

The position of benzoic acid substituents and the ability of the auxiliary ligand to act as a chelating or a bridging ligand drive metal benzoates to assemble either as discrete or as polymeric complexes.

Rhodium(ii) catalyzed synthesis of macrocycles incorporating oxindole via O–H/N–H insertion reactions

Synthesis of 10- to 29-membered oxaza-macrocyclesviaintramolecular O–H/N–H insertion reactions catalyzed by a rhodium(ii) acetate dimer is demonstrated. Synthesis of symmetric macrocyclesviahead to tail dimerization reactions is also delineated.

Recent progress towards transition metal-catalyzed synthesis of γ-lactams

The scope of transition metal-catalyzed synthesis of functionalized γ-lactams has broadened tremendously in the last decade (see the picture). These metal-catalyzed processes are reviewed by highlighting their specificity and applicability, and the mechanistic rationale is presented where possible.

DABCO-catalyzed ring opening of activated cyclopropanes and recyclization leading to γ-lactams with an all-carbon quaternary center

A novel and efficient method for the construction of γ-lactams with an all-carbon quaternary center is developed via a DABCO-catalyzed reaction of EWG-activated cyclopropanecarboxamides and electron-deficient alkenes.

Intramolecular aromatic carbenoid insertion of biaryldiazoacetates for the regioselective synthesis of fluorenes

The rhodium- or copper-catalyzed intramolecular aromatic carbenoid insertion of biaryldiazoacetates offers a convenient route to fluorene carboxylates with high yields. Whereas, thermal conditions provided a mixture of two regioisomeric products when substituted biaryldiazoacetates were employed as substrates. The developed catalytic conditions displayed an excellent level of regioselectivity, presumably owing to steric effects. The insertion mechanism was assumed to be an electrophilic aromatic substitution, which was supported by preliminary mechanistic studies. A chloro-substituted fluorene derivative was efficiently synthesized and utilized as a base-sensitive protecting group of amines.

Total syntheses of (-)-alpha-kainic acid and (+)-alpha-allokainic acid via stereoselective C-H insertion and efficient 3,4-stereocontrol

Reported herein is a novel approach to the total syntheses of (-)-alpha-kainic acid and (+)-alpha-allokainic acid, where the stereochemistries on C(2), C(3), and C(4) of the pyrrolidine core were introduced efficiently and selectively. A regio- and stereoselective C-H insertion reaction was utilized to prepare the gamma-lactam as an intermediate. A Michael-type cyclization of phenylsulfone with a conjugated acetylenic ketone was developed to prepare the tricyclic ketone as a key intermediate for (-)-alpha-kainic acid. Subsequently, a stereoselective dephenylsulfonylation was carried out successfully to secure the cis relationship at C(3) and C(4) centers. An unprecedented acetylation on the phenylsulfone, followed by a stereoselective dephenylsulfonylation, secured the trans relationship at C(3) and C(4) centers in (+)-alpha-allokainic acid.

2-Diazoacetoacetic acid, an efficient and convenient reagent for the synthesis of alpha-diazo-beta-ketoesters

The formation of various alpha-diazo acetoacetic esters can be obtained in a single transformation with good to excellent yields using readily available 2-diazoacetoacetic acid.

Ruthenium-Catalyzed Stereoselective Intramolecular Carbenoid C−H Insertion for β- and γ-Lactam Formations by Decomposition of α-Diazoacetamides

[reaction: see text] An operationally simple catalytic system based on [RuCl(2)(p-cymene)(2)] was developed for stereoselective cyclization of alpha-diazoacetamides by intramolecular carbenoid C-H insertion, and beta-lactams were produced in excellent yields and >99% cis-stereoselectivity. The Ru-catalyzed reactions can be performed without the need for slow addition of diazo compounds and inert atmosphere. With alpha-diazoanilides as substrate, the carbenoid insertion was directed selectively to aromatic C-H bond leading to gamma-lactam formation (>95% yield).

Rh(ii) catalysed intramolecular C–H insertion of diazo substrates in water: a simple and efficient approach to catalyst reuse

Water is an efficient solvent for the Rh2(OAc)4 catalysed intramolecular C-H insertion of a range of diazo substrates without competitive water insertion. Due to the high solubility and stability of the catalyst in water, the catalyst can be efficiently reused.

Solvent-Dependent Coordination Polymers: Cobalt Complexes of 3,5-Dinitrobenzoic Acid and 3,5-Dinitro-4-methylbenzoic Acid with 4,4‘-Bipyrdine

The synthesis, structure elucidation, and analysis of the self-assembly of Co(II) complexes of 3,5-dinitrobenzoic acid and 3,5-dinitro-4-methylbenzoic acid with 4,4'-bipyridine have been reported. Formation of the complexes and the self-assembly in the three-dimensional structures have been found to be dependent on the solvents (such as acetone, dimethly sulfoxide, etc.) employed for the synthesis of the aggregates. 3,5-Dinitrobenzoic acid forms two coordination polymers, 1a and 1b, from methanol and a mixture of methanol and acetone solvents, respectively, with entirely different recognition patterns. Similarly, 3,5-dinitro-4-methylbenzoic acid also forms two coordination complexes, 2a and 2b, incorporating the solvent of the reaction medium into the crystal lattice. Complex 2a forms a solvated channel structure, whereas 2b gives a bilayered structure, with the layers being separated by solvent of crystallization (dimethyl sulfoxide) molecules. All the complexes have been characterized by single-crystal X-ray diffraction studies. Complexes 1b, 2a, and 2b crystallize in a monoclinic lattice, but 1a adopts a tetragonal lattice. The unit cell dimensions are, for 1a, a = 8.095(1) A, b = 8.095(1) A, c = 46.283 (6) A, alpha = 90 degrees, beta = 90 degrees, and gamma = 90 degrees (space group P4(3)2(1)2, Z = 4), for 1b, a = 22.774(2) A, b = 11.375 (1) A, c = 22.533(2) A, alpha = 90 degrees, beta = 104.15(1) degrees, and gamma = 90 degrees (space group P2(1)/c, Z = 4), for 2a, a = 17.657(6) A, b = 18.709(4) A, c = 21.044(6) A, alpha = 90 degrees, beta = 108.68(3) degrees, and gamma = 90 degrees (space group, C2/c, Z = 8), and, for 2b, a = 11.025(5) A, b = 15.139(4) A, c = 11.443(4) A, alpha = 90 degrees, beta = 97.48(3) degrees, and gamma = 90 degrees (space group P2/n, Z = 2). In all the complexes 1a, 1b, 2a, and 2b, the basic interaction between Co(II) and 4,4'-bipyridine remains the same with the formation of linear Co-N dative bonds, but the carboxylates display various modes of interaction with Co(II). The average Co-N and Co-O distances are 2.161 and 2.108 A, respectively.

Gamma-lactam synthesis via C-H insertion: elaboration of N-benzyl protecting groups for high regioselectivity toward the total synthesis of rolipram

By intramolecular C-H insertion of alpha-diazo-alpha-(phenylsulfonyl)acetamides, gamma-lactams such as the antidepressant agent rolipram were efficiently synthesized in a highly regioselective manner. N-Benzyl moieties were elaborated as amide protecting groups to enhance regioselectivity in C-H activation as well as chemoselectivity over addition reactions. [reaction: see text]

First direct reductive amination of mucochloric acid: a simple and efficient method for preparing highly functionalized alpha,beta-unsaturated gamma-butyrolactams

[reaction: see text] The first direct reductive amination of mucochloric acid (1) has been accomplished. Reaction of 1 with various alkyl, aryl, and benzylamines, followed by reduction in the same pot, provides an efficient method of obtaining N-benzyl-3,4-dichloro-1,5-dihydro-pyrrol-2-one and N-aryl (or alkyl)-3,4-dichloro-1,5-dihydro-pyrrol-2-ones.

A novel synthetic route to chiral gamma-lactams from alpha-amino acids via Rh-catalyzed intramolecular C-H insertion

Highly functionalized gamma-lactams are key intermediates for the synthesis of numerous biologically significant natural products. We herein described the synthesis of various chiral gamma-lactams via intramolecular C-H insertion of alpha-diazo-alpha-(phenylsulfonyl)acetamides derived from alpha-amino acids, which possess various functional groups. The cyclizations were highly regio- and stereoselective to afford chiral gamma-lactam motifs in high yields.