Carbanion-Accelerated Claisen Rearrangements. 4. Asymmetric Induction via l,3,2-Oxazaphosphorinanes^la

The anions dervied from allyl vinyl ethers 1 and 2 undergo rapid and highly selective Claisen rearrangements. The degree of asymmetric induction has been found to be uniformly high (ca. 90:10) for various substituent patterns but depends markedly on the presence of lithium cations. The absolute sense of asymmetric induction has been established using chiral, nonracemic 1.3.2- oxazaphosphorinane 2. Two proposals for the transition structures of the phosphorus-stabilized anions are discussed.