Furopyridines. XXIX. Reactions of furo[2,3‐b:4,5‐c‘]‐, ‐[3,2‐b:‐4,5‐c’]‐, ‐[2,3‐c:4,5‐c‘]‐ and ‐[3,2‐c:3,2‐c’]dipyridine

Abstract

AbstractFuro[2,3‐b:4,5‐c‘]‐ 1a, ‐[3,2‐b:4,5‐c’]‐ 1b, ‐[2,3‐c:4,5‐c‘]‐ 1c and ‐[3,2‐c:4,5‐c’]dipyridine 1d were derived to the N‐oxides 2a‐d, N‘‐oxides 2′b, 2′c or N,N’‐dioxide 3b‐d by N‐oxidation with m‐chloroperbenzoic acid. Chlorination of these N‐oxides, N′‐oxide and N,N′‐dioxides with phosphorus oxychloride afforded compounds chlorinated at the α‐position(s) to the ring nitrogen 4a‐d, 4′c, 14b‐d and 14′b. Acetoxylation of N‐oxides 2a‐d and 2′c with acetic anhydride gave the corresponding pyridone compounds 6a‐d and 6′c in good yields, while the acetoxylation of N,N′‐dioxides gave a complex mixture from which no compound could be isolated. Cyanation of 2a‐d, 2′c and 3b‐d with trimethylsilyl cyanide yielded the cyano compounds 7a‐d, 7′c, cyano‐N‐oxides 15b‐d and dicyano compounds 15′c and 15′d. Monocyano compounds 7a‐d and 7′c were converted to the imino esters 8a‐d and 8′c by treatment with sodium ethoxide. Imino esters were derived to the carboxylic esters 9a‐d and 9′c, from which the corresponding alde hydes 10a‐d and 10′c were obtained by reduction with diisobutylaluminum hydride. Dicyanide 15′c was converted to dialdehyde 19 by the treatment with sodium ethoxide, and the subsequent hydrolysis of the imino ester and reduction of the carboxylic ester with diisobutylaluminum hydride.