A Versatile Hexadiene Synthesis by Decarboxylative sp~3-sp~3 Coupling/Cope Rearrangement

摘要

The sp3–sp3 coupling of two allyl fragments is a potentially powerful way of generating 1,5-dienes, which are found in a host of biologically active natural products.[1]However, there are surprisingly few catalytic transformations that couple two different allyl groups with high selectivity.[2–4] Seminal studies by Schwartz showed that electrophilic p-allyl palladium complexes, which are conveniently accessed by oxidative addition of allylic acetates, underwent stoichiometric coupling with nucleophilic magnesium allyl reagents.[4] Presumably this reaction proceeds by transmetalation from Mg to give bis(allyl) palladium complexes which reductively eliminate the hexadiene.[5] Transmetalation from tin was also possible, and allowed the catalytic Stille-type coupling of allylic bromides with allyl stannanes.[4] However, this method is clearly nonideal because it suffers from poor yields and requires the synthesis and use of stoichiometric quantities of toxic allyl stannanes.