Dioxopyrrolines. XLIX. Synthesis of azatropolones via photocycloaddition of 5-aryl-4-ethoxycarbonyl-1H-pyrrole-2,3-diones to acetylenes and ethylenes.
作者:Takehiro SANO、Yoshie HORIGUCHI、Yoshisuke TSUDA
DOI:10.1248/cpb.38.3283
日期:——
The first synthesis of derivatives of azatropolone, a new nitrogen heterocycle, and some of their chemical properties are described. Two routes to the azatropolone skeletone were developed; one is the photocycloaddition of dioxopyrrolines 1 to acetylenes followed by thermolysis or photolysis of the resulting cyclobutenes 2 to give the azatropolones 7 or 8, and the other is the ring expansion reaction of the cyclobutanes 5 obtained by the photocycloaddition of 1 to olefins followed by 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone dehydrogenation of the resulting dihydroazepines 16 to give the azatropolones 7.The azatropolone rapidly consumed diazomethane; thus 7 gave the 3-O-methylazatropolones 18, while 8 gave mixtures of 3-O-methyl-19 and 2-O-methylazatropolones 20. The position of methylation was proved by the unambiguous synthesis of 18 and of 2-O-ethyl derivatives 24 from 16. The azatropolones 7 and 8, when treated with a protonic solvent, readily underwent a ring contraction reaction giving rise to the pyridine-2-carboxylates 29 and 30, respectively, thus demonstrating that the azatropolone nucleus has a strongly electrophilic character.