2,5-disubstituted furans from acid catalyzed addition of alpha,beta-enones to furan, applications to the synthesis of C-2-symmetric compounds

The scope of the double addition of alpha,beta-unsaturated carbonyl compounds to furan has been investigated in water under acid catalysis. Two representative adducts (i.e. the ones to acrolein and 3-butenone 4a,b), subjected to Diels-Alder cycloaddition with a number of dienophiles, showed modest to null propensity to react. In the case of (E)-dicyanoethylene the Diels-Alder adducts readily undergo cycloreversion. Retro-Diels-Alder reaction is also observed in the intramolecular case of furan 6. The double adducts 4a,b, transformed from dienes into dienophiles by the reaction with m-chloroperbenzoic acid, readily undergo cycloaddition with 1,3-cyclohexadiene affording adducts 10, 14a,b which were hydrogenated to the C-2-symmetric compounds 11 and 15a,b.