The reaction of o-ethynylphenols 3 with a wide variety of unsaturated halides or triflates 6 in the presence of Pd(OAc)2(PPh3)2, CuI, and Et3N (procedure A) gives 2-vinyl- and 2-arylbenzo[b]furans 7, in good to high yield, through a palladium-catalyzed coupling followed by an in situ cyclization step. Small amounts of 2,3-disubstituted-benzo[b]furans 8 are usually isolated as side products. In some cases, however, compounds 8 are generated in significant yield or even as the main products. The formation of 8 can be prevented by employing alternative procedures (B and C) that use o-((trimethylsilyl)ethynyl)phenyl acetates 5 as starting building blocks. Procedure B is based on the palladium-catalyzed reaction of 5 with 6 in the presence of Pd(PPh3)4, Et3N, and n-Bu4NF, followed by the hydrolysis of the resultant coupling derivative 12 under basic conditions. Procedure C affords 7 through an in situ coupling/cyclization of 5 with 6 in the presence of Pd(PPh3)4 and KOBut. The utilization of o-alkynylphenols 9 as the starting alkynes in the palladium-catalyzed reaction with 6 leads to the formation of 2,3-disubstituted-benzo[b]furans 13 through an annulation process promoted by σ-vinyl- and σ-arylpalladium complexes generated in situ. The best results in this case are obtained by using KOAc and Pd(PPh3)4. In the presence of KOAc and Pd(PPh3)4, and under an atmosphere of carbon monoxide, the reaction of o-alkynylphenols with 6 provides 2-vinyl- and 2-aryl-3-acylbenzo[b]furans 14.

A general one-pot synthesis of pyridines 4a-t from the reaction of dialkyl acyclic/cyclic ketones 1a-i, methyl, aryl/heteroaryl ketones 1m-r, and aldehydes bearing alpha-hydrogens 1s,t with propargylamine 2 is described. Gold and copper salts are efficient catalysts for the reaction of ketones with 2. The formation of the pyridines 4 is suggested to proceed through the sequential amination of carbonyl compounds followed by regioselective 6-endo-dig cyclization of the N-propargylenamine (N-propargyldienamine) intermediate 3(5) and aromatization reaction. Whereas the preparation of linear polycyclic pyridine 4i can be carried out by reacting cholestan-3-one 1i with 2, the angular polycyclic pyridine 4j has been obtained starting from cholest-5-en-3-one 1j. Selectivity of the reaction of polycyclic dicarbonyls 1k,l with 2 has also been investigated.

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[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.

The 5-endo-dig-iodocyclization of o-alkynylphenols with iodine in the presence of NaHCO 3 at room temperature produces functionalised 2-substituted-3-iodobenzo[b]furans, which are useful synthetic intermediates for the preparation of 2,3-disubstituted benzo[b]furans via palladium-catalysed reactions.

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