Synthesis of bicyclo[3,3,1]nona-3,7-diene-2,6-diones and bicyclo[3,3,1]-nona-3,6-diene-2,8-diones

Abstract

Dehydration of the 2 : 1acetylacetone–formaldehyde adduct gives both 4,8-dimethylbicyclo[3,3,1]nona-3,7-diene-2,6-dione (1b) and 4,6-dimethylbicyclo[3,3,1]nona-3,6-diene-2,8-dione (2b). The 9-methyl analogues are obtained when formaldehyde is replaced by acetaldehyde and the 9-phenyl analogues when benzaldehyde is used. Bicyclo[3,3,1]nona-3,7-diene-2,6-dione (1a) is obtained from the dienol acetate of bicyclo[3,3,1]nonane-2,6-dione by bromination with N-bromosuccinimide and hydrolysis of the intermediate bromo-enol acetate. Structures are assigned to the bicyclic ketones by analysis of the n.m.r. spectra. Anomalous features of their u.v. spectra are noted. Reduction of the bicyclo[3,3,1]nona-3,6-diene-2,8-diones by mercuric chloride and magnesium in pyridine gives tricyclo[3,3,1,0^2,8]nona-4,6-diones.