76% 9% observed (eq 3).'0 A similar observation was made with vinylic silanes of the type A! te3SiCH= CHR. A mixture of cis-and trans-propenyltrimethylsilane gave only the expected C= C addition productsj9 as did a mixture of trans-R4eaSiCH= CHC4H9-n and Me3Si-(n- C4Hg) C= CHZ (eq 4). In contrast, the tertiary