Highly Diastereoselective Intramolecular Allylation Reactions of Mixed Silyl-Substituted Acetals
摘要:
The reaction of preformed mixed acetals derived from (alpha-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 S-E' 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 (alpha-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 (alpha-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.
A direct conversion of (α-hydroxyalkyl)silanes to carboxylic acids
作者:Russell J. Linderman、Kangyi Chen
DOI:10.1016/s0040-4039(00)61771-9
日期:1992.11
(alpha-hydroxyalkyl)trialkylsilanes and acylsilanes are readily oxidized to the corresponding carboxylic acid using ozone.
LINDERMAN, RUSSELL J.;GHANNAM, AMEEN, J. AMER. CHEM. SOC., 112,(1990) N, C. 2392-2398
作者:LINDERMAN, RUSSELL J.、GHANNAM, AMEEN
DOI:——
日期:——
Synthetic utility and mechanistic studies of the aliphatic reverse Brook rearrangement
作者:Russell J. Linderman、Ameen Ghannam
DOI:10.1021/ja00162a048
日期:1990.3
Highly Diastereoselective Intramolecular Allylation Reactions of Mixed Silyl-Substituted Acetals
作者:Russell J. Linderman、Kangyi Chen
DOI:10.1021/jo9517048
日期:1996.1.1
The reaction of preformed mixed acetals derived from (alpha-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 S-E' 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 (alpha-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 (alpha-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.