LEWIS-ACID MEDIATED REACTION OF SELENOACETALS WITH ALLYLSILANES AND ALLYLSTANNANES - SYNTHESIS OF HOMOALLYLSELENIDES

Selenoacetals react with allytrimethylsilane in the presence of tin te trachloride to produce homoallyl selenides in moderate to good yields. Aliphatic acetals react less efficiently than do aromatic ones, espec ially when steric factors can play a significant role. The use of ally l stannanes as nucleophiles is complicated by transmetallation side re actions with Lewis acids; in the case of tin tetrachloride this is the only observable transformation. However, non transmetallating Lewis a cids such as BF3 . OEt2, ZnCl2, AlCl3, etc... also allow the synthesis of homoallyl selenides from selenoacetals and allyl stannanes. The re action of bis(methylseleno)phenylmethane with tributylcrotylstannane g ave a diastereo-isomeric mixture of homoallyl selenides where the syn isomer predominated (syn/anti = 70/30), whereas the reverse stereosele ctivity was observed for the reaction of 1,1-bis(methylseleno)-2-pheny lpropane with allyltributylstannane.