A regioselective entry to vinyl lithiums from unsymmetrical ketones via enol triflates

Convergent and Efficient Total Synthesis of (+)-Heilonine Enabled by C-H Functionalizations

We report a convergent and efficient total synthesis of the C-nor D-homo steroidal alkaloid (+)-heilonine with a hexacyclic ring system, nine stereocenters, and a trans-hydrindane moiety. Our synthesis features four selective C-H functionalizations to form key C-C bonds and stereocenters, a Stille carbonylative cross-coupling to connect the AB ring system with the DEF ring system, and a Nazarov cyclization to construct the five-membered C ring. These enabling transformations significantly reduced functional group manipulations and delivered (+)-heilonine in 11 or 13 longest linear sequence (LLS) steps.

Total Syntheses of Rhodomollins A and B

The first and asymmetric total syntheses of rhodomollins A and B, two rhodomollane type grayanoids featuring a d-homograyanane carbon skeleton and an oxa-bicyclo[3.2.1] core, were accomplished via a convergent strategy. A Stille coupling and a lithium-halogen exchange/intramolecular nucleophilic addition to the aldehyde sequence were employed to assemble two enantioenriched fragments. The oxa-bicyclo[3.2.1] core was achieved through an intramolecular SN2 substitution of cyclic sulfate of 1,2-diols (Williamson ether synthesis). The A ring oxidation states were adjusted by a Payne/Meinwald rearrangement sequence and subsequent redox transformations.

Total Synthesis of Mollanol A

Mollanol A is the first isolated member of the mollane-type grayanoids which possesses an unprecedented C-nor-D-homograyanane carbon skeleton and an 5,8-epoxide. Due to its transcriptional activation effects on the Xbp1 upstream promoters in different cell types, it has a potential therapeutic effect on inflammatory bowel disease. Here we report the first total synthesis of mollanol A, which constitutes a 15-step synthesis from commercially available materials via a convergent strategy. The synthesis involves an InCl₃-catalyzed Conia-ene cyclization reaction to construct the bicyclo[3.2.1]octane moiety and a vinylogous aldol reaction/intramolecular oxa-Michael addition sequence to rapidly assemble the oxa-bicyclo[3.2.1] core.

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.

Synthesis of the Core Framework of the Cornexistins by Intramolecular Nozaki-Hiyama-Kishi Coupling

A new and direct approach to the construction of the core framework of the herbicidal natural products cornexistin and hydroxycornexistin has been developed. Formation of the nine-membered carbocycle found in the natural products has been accomplished by an intramolecular Nozaki-Hiyama-Kishi reaction between a vinylic iodide and an aldehyde. Good yields of carbocyclic products were obtained from the reaction, but diastereomeric mixtures of allylic alcohols were produced. The cyclisation reaction was successful irrespective of the relative configuration of the stereogenic centres in the cyclisation precursor.

A Stereoselective Route to (E)-Vinylstannanes by Cross-Coupling Reaction of Stannyl-Vinyldialkylboranes with Alkylating Agents

Stereoselective cross-coupling of (E)-stannylvinyldialkylboranes with alkylating agents in the presence of NaOMe and [CuBr (SMe2)] is accomplished.

Synthesis of Aryl Trimethylstannane via BF3·OEt2-Mediated Cross-Coupling of Hexaalkyl Distannane Reagent with Aryl Triazene at Room Temperature

BF₃·OEt₂-mediated cross-coupling of (SnMe₃)₂ with aryl triazene offers a new strategy for the synthesis of aryl stannane. A variety of synthetically useful aryl trimethylstannanes were produced in moderate to good yields with this metal-free approach. One-pot sequential Stille cross-coupling with different aryl bromides provides a short entry to both symmetrical and unsymmetrical biaryl compounds.

Addition of arylstannanes to alkynes giving ortho-alkenylarylstannanes catalysed cooperatively by a rhodium complex and zinc chloride

The reaction of arylstannanes ArSnR3 with unfunctionalised alkynes was found to proceed in the presence of a rhodium catalyst and a catalytic amount of zinc chloride to give ortho-alkenylarylstannanes with high selectivity in high yields. The catalytic cycle is very unique, consisting of three transmetalation steps, from Sn to Rh, Rh to Zn, and Zn to Sn, in addition to arylrhodation of alkyne followed by 1,4-migration of Rh from 2-arylalkenyl carbon to ortho-alkenylaryl carbon.

A synthesis-enabled relative stereochemical assignment of the C1-C28 region of hemicalide

Through synthesising both candidate diastereomers of a model C1-C28 fragment of the potent cytotoxic marine polyketide hemicalide, an assignment of the relative configuration between the C1-C15 and C16-C26 regions has been achieved. By detailed NMR comparisons with the natural product, the relative stereochemistry between these two 1,6-related stereoclusters is elucidated as 13,18-syn rather than the previously proposed 13,18-anti relationship. A flexible and modular strategy using an advanced C1-C28 ketone fragment 22 is outlined to elucidate the remaining stereochemical features and achieve a total synthesis.

Simple and Efficient Generation of Aryl Radicals from Aryl Triflates: Synthesis of Aryl Boronates and Aryl Iodides at Room Temperature

Despite the wide use of aryl radicals in organic synthesis, current methods to prepare them from aryl halides, carboxylic acids, boronic acids, and diazonium salts suffer from limitations. Aryl triflates, easily obtained from phenols, are promising aryl radical progenitors but remain elusive in this regard. Inspired by the single electron transfer process for aryl halides to access aryl radicals, we developed a simple and efficient protocol to convert aryl triflates to aryl radicals. Our success lies in exploiting sodium iodide as the soft electron donor assisted by light. This strategy enables the scalable synthesis of two types of important organic molecules, i.e., aryl boronates and aryl iodides, in good to high yields, with broad functional group compatibility in a transition-metal-free manner at room temperature. This protocol is anticipated to find potential applications in other aryl-radical-involved reactions by using aryl triflates as aryl radical precursors.

An Expedient Total Synthesis of Chivosazole F: an Actin-Binding Antimitotic Macrolide from the Myxobacterium Sorangium Cellulosum

A unified strategy for the chemical synthesis of the chivosazoles is described. This strategy is based on two closely related approaches involving the late‐stage installation of the isomerization‐prone (2Z,4E,6Z,8E)‐tetraenoate motif, and an expedient fragment‐assembly procedure. The result is a highly convergent total synthesis of chivosazole F through the orchestration of three mild Pd/Cu‐mediated Stille cross‐coupling reactions, including the use of a one‐pot, site‐selective, three‐component process, in combination with controlled installation of the requisite alkene geometry.

Synthesis of aryl trimethylstannanes from aryl halides: an efficient photochemical method

An efficient transition-metal-free photochemical method featuring excellent functional group tolerance, mild reaction conditions and short reaction times has been discovered and developed for the synthesis of (hetero)aryl trimethylstannanes from (hetero)aryl halides.

Synthesis of aryl trimethylstannanes from aryl amines: a Sandmeyer-type stannylation reaction

Sandmeyer-type stannylation: Stille coupling is one of the most powerful coupling reactions for CC bond formation, whereas there are only limited methods to access aryl stannane compounds. A mild stannylation process based on a Sandmeyer-type transformation using aromatic amines as the starting materials is described. DCE: 1,2-dichloroethane.

Studies toward welwitindolinones: formal syntheses of N-methylwelwitindolinone C isothiocyanate and related natural products

The formal syntheses of N-methylwelwitindolinone C isothiocyanate (4) and several other welwitindolinones 5-8 were achieved by the independent synthesis of 79. The synthesis featured a Lewis acid-mediated coupling between a heteroaryl carbinol and bis-TMS enol ether, an intramolecular enolate arylation, and an unprecedented intramolecular allylic alkylation of a γ-acyloxyenone.

Total synthesis of (+)-spirastrellolide A methyl ester: Challenges and discoveries

This review focuses on recent synthetic efforts by our group towards spirastrellolide A methyl ester, a complex marine macrolide containing two spiroacetal ring systems that shows promising anticancer properties. The evolution of a flexible, modular strategy leading to the first total synthesis of (+)-spirastrellolide A methyl ester, and the associated challenges overcome, are highlighted, particularly in dealing with the initial structural ambiguities. This work enabled the development of an improved second-generation synthesis, which revealed a critical dependence of the key macrolactonization step on the nature of the protecting groups in the linker region between the spiroacetal motifs.

Ruthenium-catalyzed transformation of aryl and alkenyl triflates to halides

Aryl triflates were transformed to aryl bromides/iodides simply by treating them with LiBr/NaI and [Cp*Ru(MeCN)(3)]OTf. The ruthenium complex also catalyzed the transformation of alkenyl sulfonates and phosphates to alkenyl halides under mild conditions. Aryl and alkenyl triflates undergo oxidative addition to a ruthenium(II) complex to form η(1)-arylruthenium and 1-ruthenacyclopropene intermediates, respectively, which are transformed to the corresponding halides.

The stereocontrolled total synthesis of spirastrellolide A methyl ester. Expedient construction of the key fragments

Due to a combination of their promising anticancer properties, limited supply from the marine sponge source and their unprecedented molecular architecture, spirastrellolides represent attractive and challenging synthetic targets. A modular strategy for the synthesis of spirastrellolide A methyl ester, which allowed for the initial stereochemical uncertainties in the assigned structure was adopted, based on the envisaged sequential coupling of a series of suitably functionalised fragments; in this first paper, full details of the synthesis of these fragments are described. The pivotal C26-C40 DEF bis-spiroacetal was assembled by a double Sharpless asymmetric dihydroxylation/acetalisation cascade process on a linear diene intermediate, configuring the C31 and C35 acetal centres under suitably mild acidic conditions. A C1-C16 alkyne fragment was constructed by application of an oxy-Michael reaction to introduce the A-ring tetrahydropyran, a Sakurai allylation to install the C9 hydroxyl, and a 1,4-syn boron aldol/directed reduction sequence to establish the C11 and C13 stereocentres. Two different coupling strategies were investigated to elaborate the C26-C40 DEF fragment, involving either a C17-C25 sulfone or a C17-C24 vinyl iodide, each of which was prepared using an Evans glycolate aldol reaction. The remaining C43-C47 vinyl stannane fragment required for introduction of the unsaturated side chain was prepared from (R)-malic acid.

Total synthesis of (-)-N-methylwelwitindolinone C isothiocyanate

We report the first total synthesis of (-)-N-methylwelwitindolinone C isothiocyanate. Our route features a number of key transformations, including an indolyne cyclization to assemble the [4.3.1]-bicyclic scaffold, as well as a late-stage intramolecular nitrene insertion to functionalize the C11 bridgehead carbon en route to the natural product.

Ni, Co, and Mo-metal-catalyzed alkynes hydrostannations using Bu(3)SnCl/PMHS/KF/18-crown-6 as an in situ Bu(3)SnH source

A number of terminal alkynes were subjected to nickel, cobalt, and molybdenum catalyzed hydrostannations in presence of tributyltin chloride, polymethylhydrosiloxane, potassium fluoride and 18-crown-6 as an situ organotin hydride source to produce vinylstannanes.

Lessons Learned while Traversing the Welwitindolinone Alkaloids Obstacle Course

We recount several unexpected results observed in the course of our work toward the synthesis of welwitindolinone alkaloids. The surprising results provide an opportunity to refine one's understanding of the interplay between chemical structure and reactivity.

An improved palladium-catalyzed conversion of aryl and vinyl triflates to bromides and chlorides

A facile Pd-catalyzed conversion of aryl and vinyl triflates to aryl and vinyl halides (bromides and chlorides) is described. This method allows convenient access to a variety of aryl, heteroaryl, and vinyl halides in good to excellent yields and with greatly simplified conditions relative to our previous report.

Synthesis of the C15-C35 northern hemisphere subunit of the chivosazoles

An advanced C15-C35 subunit of the chivosazole polyene macrolides was prepared in a convergent manner, exploiting boron-mediated aldol reactions for the stereocontrolled construction of the C15-C26 and C27-C35 segments, followed by their Pd/Cu-promoted Stille coupling to configure the signature (23E,25E,27Z)-triene motif. Correlation with a known C28-C35 degradation fragment of chivosazole A was also achieved.

Palladium-catalyzed conversion of aryl and vinyl triflates to bromides and chlorides

The palladium-catalyzed conversion of aryl and vinyl triflates to aryl and vinyl halides (bromides and chlorides) has been developed using dialkylbiaryl phosphine ligands. A variety of aryl, heteroaryl, and vinyl halides can be prepared via this method in good to excellent yields.

N-(4-Chlorophenyl)-1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methanesulfonamide

The title mol­ecule, also called 4-chloro-N,N-bis­(trifluoro­methane­sulfon­yl)aniline, C₈H₄ClF₆NO₄S₂, has non-crystallographic twofold symmetry with the pseudo-axis aligned along the Cl—C⋯C—N backbone of the mol­ecule: the SO₂CF₃ residues lie to either side of the benzene ring. In the crystal, the presence of C—H⋯O contacts lead to the formation of a sequence of 12-membered {⋯HC₂NSO}₂ synthons within a supra­molecular chain aligned along [101].