Chelation-assisted carbon-carbon bond activation by Rh(I) catalysts

Herein described is the chelation-assisted C-C bond activation of unstrained ketones under the co-catalyst system of Rh(PPh3)(3)Cl and 2-amino-3-picoline (1). This reaction is based on the strategy we recently developed in hydroacylation with aldehydes in which 2-aminopyridine derivatives function as chelation-assistant tools. Unstrained ketones having a beta-hydrogen gave rise to alkyl-exchanged ketones via this C-C bond activation under an excess of external olefins. In the absence of external olefins, cycloheptanone underwent a ring contraction to generate five- and six-membered cyclic ketones. Instead of unstrained ketones, sec-alcohols were also employed as a substrate for this C-C bond activation via hydrogen transfer. The reaction of allylamine derivatives under [Rh(C8H14)(2)Cl](2) and PCy3 afforded symmetric dialkyl ketones via a series of reaction such as olefin isomerization, C-H bond activation, and C-C bond activation. The key intermediate, the imine derived from 1 was generated from a primary amine through dehydrogenation followed by transimination. Consequently, the Rh(l)-catalyzed C-C bond activation of unstrained ketones and their equivalents was demonstrated by utilizing a chelation-assistance strategy. (C) 2002 Elsevier Science B.V. All rights reserved.