Organometal‐mediated synthesis of conjugated allenynes, allenediynes, vinylallenes and diallenes

Abstract
An extensive study of the reactivity of organometallic reagents R3M (R3 = 1‐alkenyl, 1‐alkynyl, 3‐alken‐1‐ynyl, 1,3‐alkadiynyl or 1,2‐alkadienyl; M = Li, MgCl, ZnCl, Cu, Ag) towards R1R2CCCH‐X (1) and R1R2C(X)‐CCH (4) is described. High yields of R1R2CCCHR3 (2) have been obtained by reaction of 1 (X  Br) with R3‐M (M = MgCl, ZnCl or Cu1/2Li1/2) using Pd[PPh3]4 as catalyst. Similarly, pure 2 have been obtained by the Pd[PPh3]4‐catalyzed reaction of 4 (X = Br, OAc, OS(O)Me, OSO2Me, OP(O)(OEt)2) with R3‐M (M = MgCl, ZnCl, Zn1/2, Cu, Cu1/2Li1/2, Ag, or Ag1/2Li1/2). In some reactions with R3‐Cu, compounds 4 were converted into 2 in the absence of the palladium catalyst.