Allylstannation. II. A total "cis-preference" in the addition of n-Bu2ClSnCH(CH3)CHCH2 to aldehydes

1-Buten-3-yldi-n-butylchlorotin, formed by redistribution of ( E Z)-2-butenyltri-n-butyltin and Bu2SnCl2, reacts readily with neat RCHO (R C2H5, C2H5(CH3)CH, (CH3)2CH, (CH3)3C and C6H5) to give high yields (80-100%) of alcohols of the type RCH(OH)CH2CHCHCH3 only in the Z-configuration. This appears to be the first example of total "cis-preference" in the addition of Grignard-like reagents to carbonyl compounds. The results are discussed in terms of steric requirements around the tin centre which is probably five-coordinate in the transition stat