Benzotriazole-Mediated [2,3]-Wittig Rearrangement. General and Stereocontrolled Syntheses of Homoallyl Alcohols and beta,gamma-Unsaturated Ketones.
Readily accessible allyl 1-(benzotriazol-1-yl)alkyl ethers (13 and 19), upon treatment with 2.5 equiv of nucleophilic lithium reagents, give secondary and tertiary homoallyl alcohols (16 and 21), respectively, exclusively in the E configuration in excellent yields. This is achieved by deprotonation followed by [2,3]-Wittig rearrangement, departure of the benzotriazolyl group, and then nucleophilic addition to the resulting carbonyl compound. Following a similar protocol, primary E-homoallyl alcohols 18 are prepared in good yield by the reaction of ethers 13 with LDA in the presence of NaBH(4). Our approach complements the stereochemical Z-selective syntheses of primary homoallyl alcohols of Still and of Bruckner. Wittig rearrangement of the anions of 19 generated with LDA analogously furnishes E-beta,gamma-unsaturated ketones 20 in excellent yields.
Katritzky
Alan R.
AR
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200.
Wu
Hong
H
Xie
Linghong
L