COMPETITIVE ACYLATION OF ARYLSTYRYLSILANES - CONTROLLING SILANUCLEOPHILE REACTIVITY

Electrophilic substitution reactions occurred cleanly between acyl cat ions and arylstyrylsilanes 2-4. With an unsubstituted aryl group, 2 un derwent transfer of the styryl group to form styryl ketone 5 as would be predicted from previous kinetic studies. With increasing methyl gro up substitution of the aryl group, aryl group transfer occurred compet itively such that 3 showed a 2:1 preference for destyrylation : dearyl ation giving 10:11 while 4 underwent exclusive transfer of the mesityl group to give mesityl ketones 6-8, These results are not consistent w ith electrophilic aromatic substitution reactions of nonsilylated comp ounds, With increasing methyl group substitution of the aryl group, it s reactivity should increase for electronic reasons but not to the ext ent that it surpasses that of the styryl group, When the silyl group i s flanked by methyl groups, however, cleavage of the silicon-aryl bond is additionally facilitated by the relief of steric congestion such t hat this process occurs preferentially to transfer of the styryl group .