Rn. Warrener et al., MALEIMIDE-FUSED CYCLOBUTADIENES AND DEWAR FURANS - TRAPPING WITH DIENES AS A ROUTE TO PROPELLANE PHOTOSUBSTRATES WITH POTENTIAL FOR OXIREN PRODUCTION, Australian Journal of Chemistry, 48(2), 1995, pp. 241-260
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
.