Stereoelectronic control of additions of vinylmagnesium bromide to 1-methyl- and 3-methylpentacyclo[5.4.0.0(2,6)-.0(3,10).0(5.9)]undecane-8,11-dionesand to 1-methylhexacylo[10.2.1.0.0(2,11).0(4,9).0(4,14).0(9,13)]pentadeca-5,7-diene-3,10-dione

Grignard addition of excess vinylmagnesium bromide to 1-methyl- and 3-methy lpentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-diones (1a and 1b, re spectively) and to 1-methylhexacyclo[1.0.2.1.0(2,11).0(4,9).0(4,14).0(9,13) ]pentadeca-5,7-diene-3,10-dione (4) each proceed regiospecifically to affor d a single hemiketal adduct (i.e., 2a, 3a, and 5a, respectively). The struc ture of each of the three reaction products was established unequivocally v ia application of X-ray crystallographic methods. Relative energies for the model transition states obtained from geometry optimizations at the Hartre e-Fock level of theory in basis set 3-21G(d) indicate that these reactions are kinetically controlled.