IMPORTANCE OF STERIC HINDRANCE IN LINEAR COORDINATION OF LEWIS-ACIDS WITH ALPHA-ENONES

The complexation of alpha-enones [(E)-MeC(H)=C(H)COR] with SnCl4 and T iCl4 has been studied with NMR spectroscopy as well as semiempirical a nd ab initio SCF-MO methods, which indicate a preference for linear co ordination of Lewis acids with alpha-enones due to the steric effect o f R group (R = Bu(t), Ph, 2,4,6-Me(3)C(6)H(2),4-MeOC(6)H(4)) in the s- cis conformation.