ca01 only detailed ToC 1..24

1.1.3 Nickel–Alkyne Complexes 57
Scheme 43 Alkynyl Enone Cyclization with Alkylation or Reduction [90–93]
R 1
O
R 2
+ R 3 2Zn
Ni(cod) 2 2
Ni(cod)2 2, Ph3P
R 3 = Et
Scheme 44 Alkyne-Unsaturated Acyloxazolidinone Cyclizations in (+)-Æ-Allokainic Acid
Synthesis [94]
O
O N
O
N
O
O
OTBDMS
Me 3Al, Ni(cod) 2 2
O
O
N
O
O
R 1
O
R 1
O
N
HO
O
O
R 3
H
R 2
R 2
OTBDMS
HO
N
O
H
62 (+)-α-allokainic acid
Trost has developed a cycloisomerization of enynes involving a nickel–chromium catalyst
system (Scheme 45). [95] High yields among a broad range of substrates are noted.
Scheme 45 Nickel-Catalyzed Enyne Cycloisomerization [95]
OH
NiCl2(PPh3)2 3, CrCl2
Alkylative Cyclization of Alkynyl Enones; General Procedure: [91]
A 0.3–0.5 M soln of ZnCl 2 (2.5–3.0 equiv) in THF was stirred at 0 8C, and the organolithium
or Grignard reagent (3.7–4.5 equiv) was added by syringe followed by stirring for 0.25–1 h
at 0 8C. A 0.02–0.04 M soln of [Ni(cod) 2](2; 0.04–0.06 equiv) in THF was added and the resulting
mixture was immediately transferred by cannula to a 0.1–0.2 M soln of the unsaturated
substrate (1.0 equiv). After consumption of starting material as judged by TLC analysis
(typically 0.25–2.0 h at 0 8C), the mixture was subjected to an extractive workup with
NaHCO 3/EtOAc or NH 4Cl/NH 4OH buffer (pH 8) and Et 2O followed by flash chromatography
(silica gel). Although the above procedure was typically used, commercially available diorganozinc
reagents performed comparably.
OH
H
for references see p 79