Catalytic Asymmetric [4 + 1] Cycloaddition of Vinylallenes with Carbon Monoxide:  Reversal of the Induced Chirality by the Choice of Metal

Rhodium(I) and platinum(0) complexes having a chiral ligand, 1,2-bis(2,5-dialkylphosphorano)benzene, effected an asymmetric carbonylative [4 + 1] cycloaddition reaction of vinylallenes. Useful levels of asymmetric induction were attained even with substrates lacking directive heteroatom functionalities. The highest enantioselectivity of 95.0% ee was achieved in the rhodium-catalyzed reaction of a vinylallene bearing an ester group. Whereas the enantioselectivities of the rhodium-catalyzed reactions were significantly affected by the substrate structures, the platinum-catalyzed reactions generally presented good enantioselectivities over 70% ee. In particular, the observed absolute configurations were opposite to those observed in the rhodium-catalyzed reactions. The reversal of the induced chirality according to the center metal employed was interpreted mechanistically.