ORIGINS OF SELECTIVITY IN CONJUGATE ADDITIONS OF ALKENYLPHOSPHONATES TO LITHIATED BISLACTIM ETHERS - A SEMIEMPIRICAL STUDY

The stereoselective conjugate additions of alkenyl and butadienylphosp honates to lithiated bislactim ethers have been studied at the semiemp irical level. In the gas phase, an initial lithium-phosphoryl coordina tion to form a disolvated chelate complex without energy barrier is fo llowed by the rate-determining reorganization through competitive eigh t-membered cyclic transition structures. A compact vs. relaxed transit ion state model reproduces the sense and degree of the experimental st ereoselection. Copyright (C) 1996 Elsevier Science Ltd