Asymmetric Sulfur Ylide Mediated Aziridination: Application in the Synthesis of the Side Chain of Taxol

Copper(I)-Photocatalyzed Diastereoselective Aziridination of N-Sulfonyl Imines with Vinyl Azides: Application to Benzo[f][1,2,3]oxathiazepines Dioxides and Fused Isoxazolines

An in situ generated photoactive copper(I)-complex-catalyzed aziridination reaction of cyclic N-sulfonyl imines with α-aryl-substituted vinyl azides irradiated by blue-LEDs light is reported for the first time. This novel SET process represents a mild, sustainable, and pragmatic method for accessing synthetically resourceful sulfamidate-fused aziridines in acceptable chemical yields with excellent diastereoselectivities. Delightedly, pharmacologically attractive benzo[f][1,2,3]oxathiazepine dioxides and fused isoxazoline frameworks were achieved through our newly developed metal-free based ring-expansion techniques, highlighting the synthetic value of accessed aziridines. Finally, the possible mechanism for [2+1] aza-cyclization was presented based on the conduction of a series of control experiments.

Water-Mediated Intramolecular Cyclization/Oxidation of α-Carbonyl Sulfur Ylides: Synthesis of Corey-Chaykovsky Reagent Type Heterocycles

A new class of Corey-Chaykovsky reagent type five-membered heterocycles with an oxosulfonium ylide moiety has been synthesized by the water-mediated intramolecular cyclization/oxidation of α-carbonyl sulfur ylides generated in situ from sulfonium salts under mild conditions.

Landscape of Lankacidin Biomimetic Synthesis: Structural Revisions and Biogenetic Implications

In this report, a unified biomimetic approach to all known macrocyclic lankacidins is presented. By taking advantage of the thermolysis of N,O-acetal to generate the requisite N-acyl-1-azahexatriene species, we eventually realized the biomimetic Mannich macrocyclization, from which all of the macrocyclic lankacidins can be conquered by orchestrated desilylation. The reassignments of the reported structures of isolankacidinol (7 to 10) and the discovery of a recently isolated "lankacyclinol" found to be in fact 2,18-bis-epi-lankacyclinol (72) unraveled the previously underappreciated chemical diversity exhibited by the enzymatic macrocyclization. In addition, the facile elimination/decarboxylation/protonation process for the depletion of C1 under basic conditions resembling a physiological environment may implicate more undiscovered natural products with variable C2/C18 stereochemistries (i.e., 62, 73, and 75). The notable aspect provided by a biomimetic strategy is significantly reducing the step count compared with the two previous entries to macrocyclic lankacidins.

Recent progress on donor and donor-donor carbenes

Donor and donor-donor carbenes are two important kinds of carbenes, which have experienced tremendous growth in the past two decades. This review provides a comprehensive overview of the recent development of donor and donor-donor carbene chemistry. The development of this chemistry offers efficient protocols to construct a wide variety of C-C and C-X bonds in organic synthesis. This review is organized based on the different types of carbene precursors, including diazo compounds, hydrazones, enynones, cycloheptatrienes and cyclopropenes. The typical transformations, the reaction mechanisms, as well as their subsequent applications in the synthesis of complex natural products and bioactive molecules are discussed. Due to the rapidly increasing interest in this area, we believe that this review will provide a timely and comprehensive discussion of recent progress in donor and donor-donor carbene chemistry.

Diastereoselective synthesis of spiro-cyclopropanyl-cyclohexadienones via direct sulfide-catalyzed [2 + 1] annulation of para-quinone methides with bromides

A sulfide-catalyzed [2 + 1] annulation of para-quinone methides with diverse bromides was disclosed to access appealing spiro-cyclopropanyl-cyclohexadienones with high diastereoselectivity.

Diastereoselective One-Pot Synthesis of Oxazolines Using Sulfur Ylides and Acyl Imines

This work describes an extended version of the Corey-Chaykovsky reaction to access oxazolines using sulfur ylides and stable precursors of acyl imines. The reaction proceeds through a mixture of aziridines and oxazolines, which provides the trans-oxazolines following in situ Heine-type aziridine ring expansion upon treatment with BF₃·OEt₂. Following the same one-pot procedure, amidine imides react with the sulfur ylides to provide imidazolines.

Protecting group-directed annulations of tetra-substituted oxindole olefins and sulfur ylides: regio- and chemoselective synthesis of cyclopropane- and dihydrofuran-fused spirooxindoles

Protecting group-controlled regio- and chemoselective synthesis of cyclopropane- and dihydrofuran-fused spirooxindoles containing vicinal quaternary carbon centers.

One-pot diastereo- and enantioselective hydrosilylation–transacylation of α-acyloxy β-enamino esters

Asymmetric hydrosilylation–transacylation of α-acyloxy β-enamino esters provided various α-hydroxyl-β-acylamido esters in good yields with good diastereoselectivities and enantioselectivities.

Towards a General Understanding of Carbonyl-Stabilised Ammonium Ylide-Mediated Epoxidation Reactions

The key factors for carbonyl-stabilised ammonium ylide-mediated epoxidation reactions were systematically investigated by experimental and computational means and the hereby obtained energy profiles provide explanations for the observed experimental results. In addition, we were able to identify the first tertiary amine-based chiral auxiliary that allows for high enantioselectivities and high yields for such epoxidation reactions.

Asymmetric syntheses of three-membered heterocycles using chiral amide-based ammonium ylides

The use of carbonyl-stabilised ammonium ylides to access chiral glycidic amides and the corresponding aziridines has so far been limited to racemic trans-selective protocols. We herein report the development of an asymmetric approach to access such compounds with high levels of stereoselectivity using easily accessible chiral auxiliary-based ammonium ylides. The use of phenylglycinol as the chiral auxiliary was found to be superior to Evans or pseudoephedrine-based auxiliaries resulting in good to excellent stereoselectivities in both, epoxidation and aziridination reactions.

Catalysis of diazoalkane-carbonyl homologation. How new developments in hydrazone oxidation enable the carbon insertion strategy for synthesis

Diazo compounds continue both to challenge and to fascinate practitioners of chemical synthesis. The most strategically powerful and unique type of reactivity observed with these reagents is a formal insertion of the donor-acceptor carbon into C-C or C-H bonds alpha to carbonyl groups. Although the reaction does not involve discrete carbon-metal bonds, it can be catalyzed by metal-based Lewis acids. This chapter investigates both classical and modern developments in diazoalkyl carbon insertion with a special emphasis on nonstabilized nucleophiles.

Practical and highly selective sulfur ylide-mediated asymmetric epoxidations and aziridinations using a cheap and readily available chiral sulfide: extensive studies to map out scope, limitations, and rationalization of diastereo- and enantioselectivities

The chiral sulfide, isothiocineole, has been synthesized in one step from elemental sulfur, γ-terpinene, and limonene in 61% yield. A mechanism involving radical intermediates for this reaction is proposed based on experimental evidence. The application of isothiocineole to the asymmetric epoxidation of aldehydes and the aziridination of imines is described. Excellent enantioselectivities and diastereoselectivities have been obtained over a wide range of aromatic, aliphatic, and α,β-unsaturated aldehydes using simple protocols. In aziridinations, excellent enantioselectivities and good diastereoselectivities were obtained for a wide range of imines. Mechanistic models have been put forward to rationalize the high selectivities observed, which should enable the sulfide to be used with confidence in synthesis. In epoxidations, the degree of reversibility in betaine formation dominates both the diastereoselectivity and the enantioselectivity. Appropriate tuning of reaction conditions based on understanding the reaction mechanism enables high selectivities to be obtained in most cases. In aziridinations, betaine formation is nonreversible with semistabilized ylides and diastereoselectivities are determined in the betaine forming step and are more variable as a result.

Stereospecific ring expansion of chiral vinyl aziridines

In this report, it is demonstrated that chiral vinyl aziridines can be stereospecifically ring expanded. This synthetic approach allows controlled access to chiral 2,5-cis- or 2,5-trans-3-pyrroline products from starting materials with the appropriate aziridine geometry. Twenty three ring expansion examples, most of which feature a stereospecific cyclization, are presented.