Selective propargylation of carbonyl compounds and imines with barium reagents.

A Barbier-type regioselective propargylation of aldehydes and ketones with (3-bromobut-1-ynyl)trimethylsilane has been achieved using reactive barium as a low-valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of alpha,beta-unsaturated carbonyl compounds, only 1,2-adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13.