Hindered organoboron groups in organic chemistry. 23. The interactions of dimesitylboron stabilised carbanions with aromatic ketones and aldehydes to give alkenes.

Abstract

Dimesitylboron stabilised carbanions react with diarylketones to give the corresponding alkenes in mild conditions with good yields. Reactions with aromatic aldehydes are more complex, but in all cases E-alkenes are available in good yields by trapping the intermediates with chlorotrimethylsilane followed by treatment with aq. HF/CH 3CN. Treatment of the same intermediates with trifluoroacetic anhydride gives mainly the Z-alkenes. The design and mechanisms of these important processes are considered.