Manganese(III)-mediated oxidative radical cyclization .3. Synthesis of 3-azabicyclo[3.3.0]octan-2-ones and related compounds in the reaction of 1,1,6,6-tetraarylhexa-1,5-dienes with N,N'-disubstituted malonamides

The oxidation of 1,1,6,6-tetraarylhexa-1,5-dienes with manganese(III) acetate in the presence of N,N'-diarylmalonamides gave 1-(arylcarbamoyl)-8-(diarylmethylene)-3,4,4-triaryl-3-azabicyclo-[3.3.0]octan-2-ones and 4,4,9,9-tetraaryl-2,11-bis(arylimino)-3,10-dioxatricyclo[6.3.0.0(1,5)] undecanes in good to moderate yields together with 11-(arylimino)-3,4,4,9,9-pentaaryl-10-oxa-3-azatricy-clo[6.3.0.0(1,5)]undecan-2-ones, A similar reaction in the presence of N,N'-dimethylmalonamide also yielded 3-azabicyclo[3.3.0]octan-2-one derivatives. An acid-catalyzed decomposition of the tricyclic diimines in acetic acid caused ring opening, while a similar decomposition in anhydrous THF resulted in recyclization at the nitrogen atom and/or hydrolysis of one of the imine bonds. PI modification for the synthesis of 3-azabicyclo[3.3.0]octan-2-ones is discussed according to the results of the acid-catalyzed decomposition of the tricyclic imines.