MALEIMIDE-FUSED CYCLOBUTADIENES AND DEWAR FURANS - TRAPPING WITH DIENES AS A ROUTE TO PROPELLANE PHOTOSUBSTRATES WITH POTENTIAL FOR OXIREN PRODUCTION

N-Methylmaleimide-fused cyclobutadiene (15) and its 1,2-dimethyl deriv ative (41) have been generated by zinc/titanium tetrachloride treatmen t of the vicinal dibromide (39) and (24) respectively. Prior epoxidati ons of (24) and (39) produce mixtures of dibromo epoxides which yield the related N-methylmaleimide-fused Dewar furans (16) and (17) upon si milar debromination (Zn/TiCl4). None of these reactive intermediates i s sufficiently stable for direct observation, but each was trapped in adduct form by Diels-Alder reaction with furan. Attempts to form fused Dewar furan (17) by flash vacuum pyrolysis of the furan adduct (34) l ed to the production of the isomeric furo[3,4-c]pyrrole (43), the stru cture of which was confirmed by separate synthesis. Stereochemical ass ignments have been made to most adducts, and AM1 calculations have bee n used to predict the stereoselectivities and facial selectivities in these cycloaddition reactions. Reaction of these Dewar furans with cyc lopentadienones produced propellanes which were decarbonylated to thei r respective cyclohexadienes and used as photosubstrates for the gener ation of oxiren or dimethyloxiren. Attempts to trap oxiren, generated by photolysis of propellane (12), with isobenzofuran were unsuccessful .