176038-03-2Relevant articles and documents
Highly diastereoselective intramolecular allylation reactions of mixed silyl-substituted acetals
Linderman, Russell J.,Chen, Kangyi
, p. 2441 - 2453 (1996)
The reaction of preformed mixed acetals derived from (α-hydroxyalkyl)dimethylallylsilane with a number of aromatic and aliphatic aldehydes in the presence of Lewis acids results in a highly diastereoselective intramolecular allylation reaction. The reaction proceeds through a cyclic synclinal SE′ addition of the allylsilane to an intermediate oxocarbenium ion. The reaction occurs exclusively by an intramolecular process as determined by means of a cross-over experiment. The relative stereochemistry was determined by the conversion of one of the allylation products to a known (stereodefined) aldol-type product. A greater degree of diastereoselectivity is obtained by in-situ formation of an oxocarbenium ion from (α-hydroxyhexyl)dimethylallylsilane and an aldehyde in the presence of boron trifluoride etherate. The diastereoselectivity of the in-situ allylation reaction typically exceeds 100:1 in favor of the syn adduct. However, reactions with electron rich aryl aldehydes resulted in a diminished degree of diastereoselectivity. The initial product of the in-situ reaction is an unstable silyl fluoride which is readily hydrolyzed to a silanol derivative upon reaction with methanolic potassium hydroxide. The overall yield of the two-step process is greater than 80%. A method for the synthesis of more highly substituted (α-alkoxyalkyl)dimethylallylsilanes by allyl anion displacement of methoxide from silicon is also described. The methyl siloxane derivatives were obtained by ozonolytic cleavage of an unsubstituted allyl group in methanol.
