Azepinones. Part 3. Reactions of simple 1H-azepin-3(2H)-ones with electrophiles

Abstract

The dienaminone conjugated system of 1H-azepin-3(2H)-ones (1) and (2) is active towards electrophiles at either oxygen or carbon centres. Analysis of ¹H and ¹³C NMR spectra shows that O-protonation (trifluoroacetic acid) and O-alkylation (triethyloxonium tetrafluoroborate) take place. Sequential deuterium exchange at the 4-, 6- and 2-positions of (1) occurs via the free base. Treatment of (1) or (2) with N-halogenosuccinimides gives 4-halogeno and 4,6-dihalogeno products. The X-ray crystal structure of the 4-chloro derivative (11) shows that the halogen substituent has little effect on the geometry of the ring.