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

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