In order to gain more insight into the mechanistic as-pects leading to the trans arrangement from the E olefin la, we examined the reductive coupling of the 2 isomer 1b. lo The reaction proceeded rather slowly compared with the E isomer la and turned out to produce the pinacol4b as a major product (50% yield) along with a mixture of 2b (12%), carbinol 3b (9%), and y-lactone 5 (5%). This result probably suggests that the trapping of the vanadium ...
