Selectivity in reactions involving α-alkoxyallyltributyltins

Abstract

The behaviour of α-alkoxyallyltributyltins has been studied in terms of chemo-, regio- and stereoselectivity. Chemoselectivity is readily controlled by the experimental conditions, as exemplified by the reaction of p-bromobenzaldehyde with α-ethoxycrotyltributyltin. Cross-coupling products are the sole products when the reaction is catalyzed by Pd(PPh 3) 4 while the use of Lewis acids, or even simple heating of the reagents, cause addition to the aldehyde group. The regio and stereochemistries of the addition reactions can also be controlled in some circumstances. For instance, the BF 3. Et 2 O promoted reactions (CH 2 Cl 2, −78°C) lead regio- and stereoselectively to the α -glycol monoether 16E (93 % syn E). On the other hand, the (E)-α-ethoxycrotyltributyltin has been shown to be much more reactive than the (Z)- isomer. It allows highly regio and stereoselective reaction affording 19Z ( anti Z) on heating (100°C, 6 h). These results are discussed and an interpretation of the stereochemical trends is given on the basis of the interactions occurring in usually accepted transition states.