The chemistry of organoborates. Part 7. Protonation studies of alkynyltrialkylborates

Abstract

Protonation of trialkylalkynylborate salts followed by oxidation is a very general route to ketones that proceeds under mild conditions. Hydrolytic work-up gives olefins in good yields. When a phenyl group migrates then the Z-olefin results but in all other cases mixtures of isomers are obtained. However the protonation of dialkyl(phenyl-ethynyl)-(1,1,2-trimethylpropyl)borates gives Z-olefins, but from alkynyldialkyl-(1,1,2-trimethylpropyl)borates the E-olefin predominates. Different acids give different stereochemical results with simple alkynyltrialkylborate salts. The intermediate boranes, not availble by other methods, may be used to produce olefins by reaction with iodine and base.