FUROPYRIDINES 20. WITTIG-HORNER REACTION OF A PHOSPHONATE OF REISSERTANALOGS OF FURO[3,2-C]PYRIDINES, FURO[2,3-C]PYRIDINES AND FURO[3,2-B]PYRIDINES

Furo[3,2-c]- (1a), -[2,3-c]- (1b) and -[3,2-b]pyridine (1c) were react ed with isopropyl chloroformate and trimethyl phosphite to give dimeth yl bonyl-4,5-dihydrofuro[3,2-c]pyridine-4-phosphonate (2a), dimethyl b onyl-6,7-dihydrofuro[2,3-c]pyridine-7-phosphonate (2b) and dimethyl bo nyl-4,7-dihydrofuro[3,2-b]pyridine-7-phosphonate (2c) as unstable syru ps. Reaction of 2b and 2c with n-butyllithium and then with benzaldehy de, p-methoxybenzaldehyde, p-cyanobenzaldehyde or propionaldehyde affo rded the normal Wittig reaction products 5b-H, 5b-OMe, 5b-CN, 5b-Et, 5 c-H, 5c-H, 5c-OMe and 5c-CN, except for 2b with propionaldehyde. While , the same reactions of compound 2a and the reaction of 2b with propio naldehyde afforded the unexpected products, -isopropoxycarbonylfuro[3, 2-c]pyridinio-4-aryl-(or ethyl)methoxides 3a-H, 3a-OMe, 3a-CN and 3a-E t, 4-(1'-aryl(or ethyl)-1'-hydroxymethyl)furo[3,2-c]pyridines 4a-H, 4a -OMe, 4a-CN and 4a-Et accompanying formation of the normal products. T reatment of the normal Wittig reaction products with lithium diisoprop ylamide and then with acetone gave the derivatives alkylated at the 2- or the benzylic positions.