Ni-Catalyzed Reductive Homocoupling of Unactivated Alkyl Bromides at Room Temperature and Its Synthetic Application

A room-temperature
Ni-catalyzed reductive approach to homocoupling
of unactivated primary, secondary, and tertiary alkyl bromides is
described. The catalytic system can be easily generated from air-stable
and cheap materials and demonstrates broad functional group tolerance,
thus allowing facile access to useful dimeric triterpene and lignan-like
molecules. Moreover, the dimerization of tertiary bromide 6 efficiently establishes sterically hindered vicinal quaternary carbons
(C3a and C3a′), which is a key linkage of intriguing bispyrrolo­[2,3-b]­indoline alkaloids, thereby enabling us to complete the
total syntheses of racemic chimonanthine (9) and folicanthine
(10). In addition, this dimerization method can be expanded
to the highly stereoselective synthesis of bisperhydrofuro­[2,3-b]­furan (5a) and the dimeric spiroketal 5b, signifying the involvement of possible radical species.