Stereoselectivity boat-like transition structures

An appreciation of the ability of 48 to attain appreciable levels of double diastereoselection when reacted with chiral (racemic) vinyl organocerium reagents had earlier been gained in this laboratory [32]. Consequently, it occasioned no surprise to observe that 49 [33] adds to this bicyclic ketone with customary endo stereoselectivity to deliver 50 and 51 in a relative ratio of 92 8. The major product, easily purified by chromatographic means, was smoothly isomerized to 52 under anionic conditions at room temperature. For structural reasons, this sigmatropic change is required to proceed via a boat-like transition state. The all-... 

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