ca01 only detailed ToC 1..24

1.1.3 Nickel–Alkyne Complexes 59
enones (Scheme 48). [103] This latter process was found to be highly stereoselective but nonstereospecific.
Scheme 48 Partially Intramolecular [2+2+2] Cycloadditions [101–103]
R 2
TMS
O
NR 1
R 2
OTBDMS
Ph Ph
+ H H
+
+
O
O
Ni(cod)2 2
chiral phosphine
NiCl 2, Zn, ZnCl 2
80%
Ni(cod) 2 2, Ph 3P
75%
R 2
NR1 ∗
R 2
63 12−73% ee
O
O
Ph
TMS
H
64
65
OTBDMS
A fully intramolecular version involving an enediyne substrate is reported to undergo reasonably
efficient cyclization to afford the tricyclic cyclohexadiene 66 (Scheme 49). [93] Only
one example of the process is reported.
Scheme 49 Fully Intramolecular [2 + 2+2] Cycloadditions [93]
Ph
O
Ni(cod) 2 2
t-BuLi, ZnCl2 52%
Cotrimerization and Aromatization of Enones and Alkynes; General Procedure: [99]
To a soln of [Ni(acac) 2](1; 13 mg, 0.05 mmol) and Ph 3P (26 mg, 0.1 mmol) in THF (5 mL) was
added 1.0 M Me 3Al in hexane (0.4 mL) at 0 8C under N 2. After stirring for 5 min, PhOH
(92 mg, 1.0 mmol) was added to this soln, and the mixture was stirred for 5 min. To this
dark red soln were added the alkyne (2.05 mmol) and the enone (1.0 mmol) at 0 8C, and
the mixture was then stirred at rt for 2 h. DBU (350 mg, 2.3 mmol) was added to the mixture,
and the soln was opened to the air and stirred at rt overnight. Aq 0.2 M HCl (30 mL)
was added, and stirring was continued for 10 min. The aqueous layer was extracted with
Et 2O (3 ” 40 mL) and the combined organic layers were washed with aq NaHCO 3 (50 mL)
and then with brine (50 mL), dried (MgSO 4) for 30 min, filtered, and concentrated in vacuo.
The residue was purified by column chromatography (silica gel) to yield aromatic
compounds.
O
Ph
H
66
O
Ph
for references see p 79