Partially fluorinated heterocyclic compounds. Part 12. Novel internal Diels–Alder adducts via Claisen rearrangement intermediates from tetrafluoro-4- and -3-pyridyl prop-2-enyl ethers. Syntheses of tetrafluoro-3-aza- and -4-aza-tricyclo[3.3.1.0]non-3-en-6-one

Abstract

Vapour-phase thermolyses of 2,3,5,6-tetrafluoro-4-pyridyl prop-2-enyl ether and 2,4,5,6-tetrafluoro-3-pyridyl prop-2-enyl ether gave 2,4,5,7-tetrafluoro-3-azatricyclo[3.3.1.0^2,7]non-3-en-6-one (14) and 2,3,5,7-tetrafluoro-4-azatricyclo[3.3.1.0^2,7]non-3-en-6-one (21) respectively by internal Diets–Alder reactions of Claisen rearrangement intermediates. 4-Bromo-2,3,5-trifluoro-6-pyridyl prop-2-enyl ether gave 4-bromo-3,5-difluoro-3-prop-2-enyl-pyridine-2,6(1H, 3H)-dione (19) the product of hydrolysis of a Claisen intermediate. Compounds (14) and (21) underwent ready hydrolysis to the corresponding cyclic lactams, in which the ketonic carbonyl group at C-6 in both cases had also been converted into a gem-diol [compounds (15) and (22), respectively]. Hydrolytic cleavage of (22) followed by oxidative cleavage with periodic acid and reaction with diazomethane gave a trimethoxycarbonyl compound (25) containing a difluorocyclobutane ring.