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A direct and highly stereoselective route to 1-aldo and 2-keto C-glycosides has been developed by using the first example of Lewis acid induced generation of homoenolate ions from allylic ethers.As part of our ongoing interest in the development of new procedures for the preparation of C-glyc~sidesl-~ we have recently explored reaction of olefins with peracetylated g l y d . 4 By this methodology 2',3'-unsaturated C-glycosides could be produced in good to excellent yields with an high degree of stereoselectivity, allowing in addition the direct introduction of polyfunctional aglycons.We have now turned out our attention to Lewis acid induced reactions of allylic alcohols6 in order to investigate a straightforward preparation of 1-aldo and 2-keto C- glycosides.This idea originates from the reaction of diacetyl Lrhamnal(1) with 3-methyl-3-buten-1-01 (216 (eq 1) in the presence of SnC1, which shown clearly that activated olefins reacted faster than alcohols with peracetylated glycals. This result prompted us to examine analogous reactions with derivatives of 2-methyl-2-propen-1-01 (4) in order to investigate the possible direct introduction of a propionyl synthon. CI -AcO OH AcO OH A d 2 1 3 (1) Lewis acid induced addition of enolates to electrophilic carbons occupies an important position in carbon-carbon bonds formation. However despite recent progress in homoenolate chemistry'+ the generation of an homoeno-(1) Reviews: (a) Haneseian, S.; Pemet, A. G. Ado. Carbohydr. Chem. Biochem. 1976,33,111. (b) Daves, G. D.; Cheng, C. C. B o g . Med. Chem. 1976, 13, 303. (2) For some recent examples, see: (a) Lewis, M. D.; Cha, J. K.; Kishi, Y.

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