Furopyridines .21. Synthesis of cyano derivatives of furo[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine and their conversion to derivatives having another carbon-substituent

Cyanation of furo[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine N-oxides 1a, 1b and 1c by the Reissert-Henze method, reaction with benzoyl chloride and trimethylsilyl cyanide in dichloromethane and the reaction with trimethylsilyl cyanide and triethylamine in acetonitrile afforded 6-cyanofuro[2,3-b]-2a, 7-cyanofuro[2,3-c]- 2b and 4-cyanofuro[3,2-c]pyridine 2c in moderate to excellent yield. The cyano group in 2a, 2b and 2c was converted to carboxamides 3a, 3b and 3c, ethyl imidates 5a, 5b and 5c and ethyl carboxylates 6a, 6b and 6c. Reaction of the N-oxides with trimethylsily bromide in acetonitrile gave the deoxygenated furopyridine 7a and 7d, bifuropyridyl 8b and 8c, and the N-oxide 9 of 8c.