Epoxidation and Homologation of Carbonyl Compounds

Diazocyclopropane can be prepared from N-cyclopropyl-iV-nitrosourea or from the corresponding carbamates. Just as ordinary diazoalkanes, the cyclopropyldiazo compounds react with ketones with epoxide formation and homologation of the carbonyl compounds (equation 128) Readily accessible cyclopropylidenephosphoranes provide a convenient synthetic route for methylenecyclopropanes . ... 

In the past, Darzens methodology was primarily used for the synthesis of aldehydes and ketones, as a homologation reaction without any consideration of stereocontrol in the epoxide formation. For this sequence, saponification of the a,P-epoxy ester followed by decarboxylation gives the substituted carbonyl compound ... 

Diazo compounds react with aldehydes and ketones to give homologated carbonyl compounds and epoxides. Lewis acids accelerate these processes, and in some cases direct the reactions to single products. frara-Epoxides result from aldehydes and ethyldiazoacetates in the presence of MeReOs (although this can occur via a metal carbene pathway rather than a Lewis acid mechanism) [139], whereas... 

Sm-Hg/CHjlj/THF system and a n. .re pleasing. For optimal results, five sr.. .. a b>e present for each unit of the olefin, he, inbination of CHjI with MeLiLiBr carbonyl compounds into epoxides (4 eu . he one-carbon homologation of a boronic... 

Reactions.—The reaction of sulphonium ylides with carbonyl compounds to form oxirans is now a standard reaction. Among the more unusual examples reported are an intramolecular version directed towards the preparation of arene epoxide (12) (not isolable), the synthesis of the epoxide of 8-phenylthio-methylenecycloheptane, and the direct conversion of a diketone by dimethyl-sulphonium methylide into a doubly homologated hydroxymethyl aldehyde (13) by the rearrangement shown. ... 

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