Reaction of ketenes with N,N-disubstituted à-aminomethyleneketones. IX. Synthesis of 2H,5H-pyrano[3,2-c][1]benzopyran derivatives

Cycloaddition of dichloroketene to N,N-disubstituted 3-aminomethylene-4-chromanones gave in good yield N,N-disubstituted 4-amino-3,3-dichloro-3,4-dihydro-5H-pyrano[3,2-c][1]benzopyran-2-ones only in the case of aromatic N-substitution. Dehydrochlorination with triethylamine of these adducts afforded N,N-disubstituted 4-amino-3-chloro-5H-pyrano[3,2-c][1]benzopyran-2-ones in good to moderate yield. The cycloaddition to 3-dimethylaminomethylene-4-chromanone led directly to 3-chloro-4-dimethylamino-5H-pyrano[3,2-c][1]benzopyran-2-one.