ca01 only detailed ToC 1..24

64 Science of Synthesis 1.1 Organometallic Complexes of Nickel
Scheme 57 Nickel-Catalyzed Conjugate Addition of Organoaluminums [120–122]
O
O
70
71
O
O
+
+
Me 3Al
Ni(acac)2 1
87%
Me2Al Bu t
O
O
dr 1.5:1
Ni(acac) 2 1, DIBAL-H
Trimethylaluminum Conjugate Addition; General Procedure: [120]
CAUTION: Neat Me 3Al is highly pyrophoric! Appropriate safety precautions and procedures
should be adopted during all stages of the handling and disposal of this reagent.
To a stirred soln of [Ni(acac) 2](1; 128mg, 0.5 mmol), dry THF (15 mL) or EtOAc (15 mL), and
the enone (10 mmol) was added Me 3Al (1 mL, 10.5 mmol) dropwise at 0 8C. After an appropriate
time, the reaction was diluted with hexane (15 mL) and quenched by careful addition
of sat. aq NH 4Cl (1.5 mL) and worked up.
1.1.4.2.2 Variation2:
Organozincs
The conjugate addition of organozinc reagents under the influence of nickel catalysis is
by far the most widely used and most studied of the different variations. The original report
from Luche describes the conjugate addition of organozincs generated from a broad
range of alkyl, alkenyl, and aryl iodides, lithium metal, and anhydrous zinc(II) bromide to
give species such as 72 (Scheme 58). [123–125] Alternatively, the organozinc may be used as
the commercially available, salt-free organozinc, or as the in situ-generated diorganozinc
from transmetalation of zinc(II) chloride with an organolithium or organomagnesium reagent.
An interesting report from Houpis demonstrates that triorganozincates are more
effective than diorganozincs with less electrophilic substrates such as vinyl sulfoxides
and vinylpyridines (Scheme 58). [126,127] Organozinc conjugate additions have been widely
used in a variety of complex synthetic applications (Scheme 59). [128–130]
Scheme 58 Nickel-Catalyzed Conjugate Additions of Organozincs [123–127]
R 1
O
R 2
R 3 R 4
MeO
O
+
R 5 I
Li, ZnBr 2
Ni(acac) 2 1, )))
N
50−90%
R 1
67%
O
R 3
PhMgCl/ZnCl2 (3:1)
Ni(acac) 2 1
93%
72
R 4
R 2
R 5
MeO
O
O
73
Bu t
Ph
O
N