Synthesis with Organoboranes; 4. Transformation of Olefins into Homoallylic Alcohols, β,γ- and α,β-Unsaturated Ketones via Allylic Diethylboranes

Article abstract of DOI:10.1055/s-1988-27676

Allylic diethylboranes are obtained from 1-methylcycloalkenes and 2-alkenes, respectively, via metalation with trimethylsilylmethylpotassium (generated in situ from bis(trimethylsilylmethyl)mercury and potassium sand) and subsequent reaction with chlorodiethylborane.The allylic boranes react diastereoselectively with aldehydes to give homoallylic alcohols.The alcohols are oxidized with pyridinium dichromate to β,γ-unsaturated ketones, which in turn are isomerized with aluminum oxide to conjugated ketones.The transformation provides access to 2-methylene-1-acylcycloalkanes, 3-acyl-1-alkenes and 3-acyl-2-alkenes not readily available by Friedel-Crafts acylation of olefins.