Manganese(I)-Catalyzed Direct C-H Allylation of Arenes with Allenes.

Polysubstituted allyl groups, for example, the prenyl group, are valuable synthetic handles and widely encountered in bioactive compounds. Reported herein is a manganese(I)-catalyzed direct C-H coupling with allenes for the efficient assembly of allylated arenes. The protocol offers an extremely high level of atom-economy and is particularly suited for the introduction of 1,1-disubstitiuted allyl groups, as exemplified by the quantitative syntheses of a variety of prenylated indoles. The practicality of this method was evidenced by a gram-scale synthesis with a lower catalyst loading of manganese(I) (2.5 mol %, 95% yield). Experimental mechanistic studies were conducted, and a possible reaction mechanism was proposed.