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]- lb and - [3,2- c]pyridine ld afforded the 2,3-dibromo derivatives 2a, 2b and 2d, while the - [2,3-c]- compound lc 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 α-cyanopyridine compound 6a-d. Chlorination of 4a and 4d with phosphorus oxychloride gave mainly the chloropyridine derivatives 7a, 7'a and 7d, while 4b and 4c gave mainly the chlorofuran derivatives 7(b) and 7(c) accompanying formation of the chloropyridine derivatives 7b, 7'b and 7c. Acetoxylation 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 8c and 8d, acetoxyfuran 8(c) and dibromo compound 9c and 9'c.