Nucleophile Ringöffnung und Fragmentierung von 1‐Aza‐bicyclo[2.2.0]hexan Fragmentierungs‐Reaktionen, 11. Mitteilung

1‐Aza‐bicyclo[2.2.0]hexane ( 1 ) is formed in a unimolecular reaction from 2‐(2‐bromoethyl)‐azetidine ( 13 ) in aqueous or alcoholic medium. Thermal instability and high reactivity have, however, so far precluded its isolation. Hydrochloric acid, aqueous sodium hydroxide and ethanolic sodium ethoxide convert the bicyclic amine 1 into 4‐chloro‐, 4‐hydroxy‐ and 4‐ethoxy‐piperidine, ( 14 ), ( 15 ) and ( 16 ), respectively. Upon heating in solution to ca. 80° it undergoes fragmentation to N‐methylene‐3‐butenyl‐amine ( 17 ). This unusual reactivity is ascribed to strain and to concomitant weakening of the N‐C4 bond in the bicyclic amine 1 .