Stereoselective Synthesis of Conjugated Unsaturated Compounds from sec-Propargylic Alcohols

Abstract

Stereoselective routes to conjugated unsaturated compounds from sec-propargylic alcohols (1) are described. Thermal treatments of β-allenic esters, prepared by the reaction of 1 with trialkyl orthoacetates, with alumina gave (2 E, 4 Z) -alkadienoic esters with high stereoselectivity. β-Allenic amides also rearranged with alumina to give (2 E, 4 Z) -alkadienoic amides. Direct oxidation of 2, 4-alkadienoates with SeO₂ afforded furans and selenophenes. Iodolactonization of, β-allenic acids gave γ-alkylidene butenolide in one step. Stereoselective rearrangements of 2, 4-alkadienoates to 3, 5-alkadienoates with lithium diisopropylamide are described. Application of (2 E 4Z) -dienoates to the synthesis of natural products such as insect pheromones, flavors, octadecapolyenoic acids and leukotriene A₄ methyl ester are described. Base-catalyzed condensation of sec-pro-pargylic alcohols with 1-cyanopyrrolidine gave imidates, which undergo thermal rearrangement to give pyridones or dienyl-ureas. Reaction of 1-alkyn-3-ol with benzonitrile gave 4-methylene-4, 5-dihydrooxazoles, which serve as useful intermediates for the synthesis of highly functionalized oxazoles.