Furopyridines. XXVIII. Reactions of 3-bromo derivatives of furo[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridine and their N-oxides

Bromination of 3-bromofuro[2,3-b]- 1a, -[3,2-b]- 1b and - [3,2-c]pyridine I d afforded the 2,3-dibromo derivatives 2a, 2b and 2d, while the -[2,3-c]- c ompound Ic did not give the dibromo derivative. Nitration of 1a-d gave the 2-nitro-3-bromo compounds 3a-d. The N-oxides 4a-d of 1a-d were submitted to the cyanation with trimethylsilyl cyanide to yield the corresponding alpha -cyanopyridine compound 6a-d. Chlorination of 4a and 4d with phosphorus oxy chloride gave mainly the chloropytidine derivatives 7a, 7'a and 7d, while 4 b and 4c gave mainly the chlorofuran derivatives 7 " b and 7 " c accompanyi ng formation of the chloropyridine derivatives 7b, 7'b and 7c. Acetoxylatio n of 4a and 4b with acetic anhydride yielded the acetoxypyridine compounds 8a, 8'a and 8b, while 4c and 4d gave the acetoxypyridine 8'c, 8'd and 8 " d , pyridone sc and 8d, acetoxyfuran 8 " c and dibromo compound 9c and 9'c.