Lewis acid-catalyzed reactions of ethyl diazoacetate with aldehydes. Synthesis of alpha-formyl esters by a sequence of aldol reaction and 1,2-nucleophilic rearrangement

Ethyl diazoacetate reacts with a variety of aldehydes in the presence of a Lewis acid catalyst to give either beta-keto esters or alpha-formyl esters, the types of products mainly depending upon the nature of Lewis acid catal ysts employed. Reactions catalyzed by Lewis acids such as SnCl2 and SnCl4 p rovide beta-keto esters via nucleophilic 1,2-hydride migration, while those catalyzed by trimethylsilyl triflate give alpha-formyl esters via migratio n of the substituent of the aldehyde. Reaction mechanisms are discussed. (C ) 1999 Elsevier Science Ltd. All right reserved.