Ruthenium(II)-Catalyzed C-H Functionalizations with Allenes: Versatile Allenylations and Allylations.

Ruthenium(II)-catalyzed direct C-H functionalization of aromatic compounds with allenes was achieved under exceedingly mild reaction conditions to yield trisubstituted allenes. The reactions of N-methoxybenzamides proceeded smoothly in an isohypsic fashion at ambient temperature with high chemo- and regioselectivity, thereby providing a versatile means of accessing trisubstituted allenes. Detailed mechanistic studies were suggestive of a kinetically relevant C-H metalation step, which occurs by the assistance of a carboxylate moiety; this also set the stage for unprecedented C-H allylations with removable directing groups in a step-economical fashion.