ca01 only detailed ToC 1..24

52 Science of Synthesis 1.1 Organometallic Complexes of Nickel
1.1.3.3 Method 3:
Coupling of Alkynes with Isocyanides
Little is known about the mechanistic details of isocyanide–alkyne couplings. However, a
useful stoichiometric cyclization of enynes and diynes with isocyanides was developed by
Tamao and Ito, [75] and Buchwald later developed a catalytic variant (Scheme 34). [76] The resulting
cyclopentenimines may be hydrolyzed to cyclopentenones. A variety of carbocyclic
and heterocyclic templates are tolerated in the sequence.
Scheme 34 Cyclizations of Enynes and Isocyanides [75,76]
O
Ph
+
NC
Ni(cod) 2 2, bipy
Cyclization of Enynes To Form Bicyclic Cyclopentenones; General Procedure: [76]
In an inert-atmosphere glovebox, [Ni(cod) 2](2; 14 mg, 0.05 mmol), bis(diphenylmethylene)ethylenediamine
(24 mg, 0.06 mmol), the enyne (1.0 mmol), and TIPSCN (201 mg,
1.1 mmol) were dissolved in DMF (46 mL) in a 100-mL sealable Schlenk flask. The Schlenk
flask was sealed, removed from the glovebox, and heated at 110–135 8C until the enyne
was consumed (as determined by GC, 8–36 h). The flask was cooled to 0 8C, treated with
sat. aq oxalic acid (10 mL), and stirred at rt for 12–24 h. Et 2O (80 mL) and sat. aq NaHCO 3
(40 mL) were added to the soln and the layers were separated. The aqueous layer was extracted
with Et 2O (3 ” 50 mL) and the combined Et 2O extracts were washed with H 2O
(3 ” 40 mL) and brine (40 mL). The Et 2O soln was dried (MgSO 4) and concentrated in vacuo
to give an oily residue which was purified by flash chromatography (silica gel, Et 2O/hexane
1:1–2) to give the desired cyclopentenone, typically as a colorless to pale yellow oil.
1.1.3.4 Method 4:
Coupling of Alkynes with Aldehydes
Couplings of alkynes and aldehydes have been investigated in a number of contexts. Although
no metallacycles derived from oxidative couplings of one alkyne and one aldehyde
have been isolated, the reaction probably proceeds in a fashion similar to the coupling
of alkynes and carbon dioxide (Section 1.1.3.2). Tsuda and Saegusa have reported
the formal hydroacylation of alkynes by a process that involves the coupling of an alkyne
and an aldehyde (Scheme 35). [77] Two possible mechanisms are proposed for the formation
of the enone 54, and one involving the formation of an oxametallacycle is depicted.
The corresponding coupling of diynes and aldehydes is also reported by the same investigators
to afford the dihydropyran 55. [78]
80%
O
Ph
N