Catalytic Use of Elemental Gallium for Carbon–Carbon Bond Formation

The first catalytic use of Ga(0) in organic synthesis has been developed by using a Ag(I) cocatalyst, crownether ligation, and ultrasonic activation. Ga(I)-catalyzed C-C bond formations between allyl or allenyl boronic esters and acetals, ketals, or aminals have proceeded in high yields with essentially complete regio- and chemoselectivity. NMR spectroscopic analyses have revealed novel transient Ga(I) catalytic species, formed in situ through partial oxidation of Ga(0) and B-Ga transmetalation, respectively. The possibility of asymmetric Ga(I) catalysis has been demonstrated.