ON THE MAXIMUM ROTATION AND THE SOLVOBROMINATION AND SOLVOMERCURATION OF ENANTIOENRICHED 1,3-DIMETHYLALLENE

The prior assignments of the maximum rotation of enantiomerically pure 1,3-dimethylallene (13DMA) based on the methoxybromination and -mercuration of enantioenriched 13DMA are shown to be drastically in error. A value of [alpha]589 of 81.0 +/- 0.2-degrees (25-degrees-C in diethyl ether) has been determined directly on enantioenriched samples of 13DMA by the use of a chiral NMR shift reagent. The methoxybromination and -mercuration reactions, which were previously suggested to be completely stereospecific, are shown to occur with substantial losses in ee, suggesting that the intermediate onium ion intermediates undergo competitive ring opening to achiral substituted allyl cations thus resulting in loss of ee.