Synthesis of 2,4-diazabicyclo[3.3.0]octane-3,7-diones and 3-thioxo-2,4-diazabicyclo[3.3.0]octan-7-one by an intramolecular Michael-type reaction. Stability of 2,4-diaza-, 4-oxa-2-aza-, and 4-thia-2-aza-bicyclo[3.3.0]octane-3,7-diones

Abstract

Novel 2,4-diazabicyclo[3.3.0]octane-3,7-diones (10) have been prepared by an intramolecular Michael-type cyclisation. The analogous 3-thioxo-2,4-diazabicyclo[3.3.0]octan-7-one system (20) is obtained by base catalysed retro-Michael reaction of the less stable 3-arylimino-2-this-4-azabicyclo[3.3.0]octan-7-one isomer (19). The 2-aza-4-oxabicyclo[3.3.0]octane-3,7-dione system (17) is shown to be very unstable to base, fragmenting via the carbamic acid to give carbon dioxide and a 4-N-substituted cyclopent-2-enone (11). The relative stability to base of these bicyclic systems is correlated with their structure.