ca01 only detailed ToC 1..24

1.1.3 Nickel–Alkyne Complexes 51
(2,6-Dimethylpyridine)bis[phenyl(trimethylsilyl)acetylene]nickel(0) (50): [69]
PhC”CTMS (810 mg, 4.66 mmol) was added at 208C to the light yellow soln of 49 (610 mg,
2.33 mmol) in pentane (10 mL). Upon heating the mixture for a short period to 458C the
color turned intense red. Cooling to –788C afforded red cubes which were separated from
the mother liquor using a capillary frit, washed with cold pentane (2 ”), and dried in vacuo
at 208C to afford 50; yield: 960 mg (80%).
Applications of Product Subclass 3 in Organic Synthesis
1.1.3.2 Method 2:
Coupling of Alkynes with Carbon Dioxide
Nickel(0) complexes of alkynes in the presence of carbon dioxide undergo oxidative cyclization
to produce oxametallacycles 51 (Scheme 32). [70,71] Direct cleavage of the oxametallacycle
in the presence of strong acids affords unsaturated carboxylic acids 52 (Scheme
33). [72] The coupling of diynes with carbon dioxide leads to an efficient synthesis of bicyclic
Æ-pyrones such as 53 by a formal [2+2+2] cycloaddition (Scheme 33). [73,74]
Scheme 32 Coupling of Alkynes and Carbon Dioxide: Metallacycle Formation [70,71]
Me2
N
NiLn N
Me2
+
CO 2
+
Et
Et
Et
Me2 N
Ni
N O
Me2
51
Scheme 33 Coupling of Alkynes and Carbon Dioxide: Synthetic Utility [72–74]
R 1
R 1
Et
Et
+ CO 2
+ CO 2
1. Ni(cod) 2 2, bipy
2. H2SO4 Ni(cod)2 2, Cy3P
64%
R 1
H
R 1
CO2H 52
1,4-Diethyl-5,6,7,8-tetrahydro-3H-benzopyran-3-one (53): [74]
In a 50-mL stainless steel autoclave were placed, under N 2, a soln of [Ni(cod) 2](2; 0.024 g,
0.090 mmol) in THF (1.8mL), a soln of Cy 3P (0.05 g, 0.18mmol) in toluene (0.17 mL), and
THF (8.2 mL). The mixture was stirred for several min, dodeca-3,9-diyne (0.19 mL,
0.90 mmol) was added, followed by CO 2 gas to a compression of 3.7 ” 10 4 Torr at rt. The
mixture was magnetically stirred for 20 h at rt. The unreacted CO 2 gas was purged and
the mixture was transferred to a flask using Et 2O (20 mL). The soln was concentrated to
give a residue that was purified by preparative layer chromatography (hexane/Et 2O 2:1)
to give 53; yield: 0.12 g (64%).
Et
Et
53
O
O
Et
O
for references see p 79