Stereospecific Synthesis of Conjugated Dienes by Carbenoid Eliminative Cross‐Coupling Using Lithiated Allylic Carbamates

Abstract 1,2,4‐Trisubstituted 1,3‐butadienes were prepared in a stereocontrolled manner by carbenoid eliminative cross‐coupling between stereodefined lithiated secondary allylic carbamates and α‐carbamoyloxyalkyl boronates. All four geometric isomers of 4,7‐dimethyl‐1‐phenylocta‐3,5‐diene stereospecifically generated [yields 44–73 %, dr (Δ 3,4 )=84 : 16 to 97 3] appropriate combinations (S,E)‐ or (S,Z)‐i‐PrCH=CHCLi(Me)OCb with (R)‐Ph(CH 2 ) CH(Bneo)OCb. A conjugated cyclohexenylidene model diene representing the C5‐C12 domain cytotoxin callystatin A, similarly elaborated stereochemically programmed manner. The configuration 1,2‐disubstituted alkene within Li‐carbenoid was preserved product newly trisubstituted component could be selectively installed either ( E )‐ Z )‐configuration variation stereochemical pairing (like unlike) and/or mode elimination stage syn anti ).