S-Methylidene Agents: Preparation of Chiral Non-Racemic Heterocycles.

Reaction of sulfur ylide with aldehyde, imine, and ketone functionality affords the desired three-membered heterocycle in excellent yield. The sulfur ylide is generated in situ upon decarboxylation of carboxymethylsulfonium betaine functionality. Of the seven carboxymethylsulfonium betaine derivatives surveyed, the highest level of conversion of π-acceptor to heterocycle was obtained having S-methyl and S-phenyl functionality bound to a thioacetate derivative. Methylene aziridinations and epoxidations involving the decarboxylation of carboxymethylsulfonium betaine functionality complements existing technologies with the advantages of the reaction protocol, levels of conversion and scope. While moderate levels of diastereocontrol were observed in the aziridination of imine functionality, the four oxiranes resolved using Jacobsen's Co(II)-salen complex were obtained in both high yield and enantioselectivity. The isolated chiral non-racemic oxiranes constitute the formal synthesis of chelonin-B and combretastatin starting from 3-bromo-4-methoxybenzaldehyde and 3,4,5-trimethoxybenzaldehyde respectively.

Aryl-substituted sulfonium betaines: preparation and use in the epoxidation of aldehydes.

Thermally induced decarboxylation of carboxymethylsulfonium betaines results in formation of the corresponding sulfur ylides in situ. Decarboxylation rates for a range of arylcarboxymethylsulfonium betaine salts have been determined using NMR spectroscopy, and the efficiency of ylide generation and trapping has been evaluated via methylidene transfer to a range of aldehydes to form epoxides.

Sulfur ylides via decarboxylation of carboxymethylsulfonium betaines: a novel and mild protocol for the preparation of oxiranes.

A novel protocol for the generation of sulfur ylides is described. The overall process involves thermal decarboxylation of a carboxymethylsulfonium betaine to give a sulfur ylide that, in the presence of an aldehyde, affords the corresponding terminal oxirane. Yields were found to correlate with the electron deficiency of the aryl aldehyde. In situ generation of betaine in the presence of an aldehyde successfully afforded the desired oxirane in moderate yield, thus demonstrating the feasibility of a catalytic process. [reaction: see text]