摘要:
The general zinc-catalyzed allenylation of aldehydes and ketones with an allenyl boronate Is presented. Preliminary mechanistic studies support a kinetically controlled process wherein, after a site-selective Ban exchange to generate a propargyl zinc intermediate, the addition to the electrophile effectively competes with propargyl-allenyl zinc equilibration. The utility of the methodology was demonstrated by application to a rhodium-catalyzed [4 + 2] cycloaddition.