Asymmetric Isomerisation of a Cyclic Diene: a Comparative Study of BINAP and BIPNOR–Rhodium(I) Catalysts

The asymmetric isomerisation of 5,7-dibenzyloxy-6-(trialkylsilyloxy)cyclohepta-1,3-diene 1 to the corresponding 1,6-dibenzyloxy-7-(trialkylsilyloxy)cyclohepta-1,3-diene 2 can be accomplished at 90°C in a 75/25 mixture of toluene and DME in the presence of a [Rh(BIPNOR)(cod)]+ catalyst with 92% ee. A much lower ee is observed with BINAP. In both cases, the observed eeʹs increase with temperature. A mechanism involving an η5-pentadienyl–rhodium complex is proposed.