Synthesis of Highly Conjugated Arylpropenylidene-1,3-diazin-2-ones via Paterno–Büchi Reaction by Photoreaction of 5-Fluoro-1,3-dimethyluracil with 1-Methoxynaphthalenes
Synthesis of Highly Conjugated Arylpropenylidene-1,3-diazin-2-ones via Paterno–Büchi Reaction by Photoreaction of 5-Fluoro-1,3-dimethyluracil with 1-Methoxynaphthalenes
In contrast to photoreactions of 5-fluoro-1,3-dimethyluracil (5-FDMU) with various naphthalenes including 2-methoxynaphthalenes that proceeds in a manner to give ethenoquinazolines through 1,4-cycloaddition, UV-irradiation of a mixture of 5-FDMU and naphthalenes with a methoxy group at C-1 gave rise to the formation of novel cycloadducts, methyl 2-[(1E)-3-(5-fluoro-1,3-dimethyl-2-oxo-1,3-dihydropyrimidin-4-ylidene)prop-1-enyl]benzoates, derived from the novel aromatic Paterno–Büchi type cycloaddition, followed by a concomitant disruption of the initially formed oxetane moiety.
Photocycloaddition of 5-fluoro-1,3-dimethyluracil (5-FDMU) with various methoxy and dimethoxynaphthalenes was investigated. Reaction of 5-FDMU with 1,x-dimethoxynaphthalenes (x = 4-7) gave rise to the selective formation of cycloadducts, conjugated arylpropenylidene-1,3-diazin-2-ones, which were derived from an initially formed oxetane moiety via the Paterno-Buchi reaction cycloadduct. The present study shows that the presence of a methoxy substituent on the alpha-position in naphthalene is essential for the formation of products through the Paterno-Buchi reaction. This unique photoreaction involving formation of an oxetane between 5-FDMU and a naphthalene ring, followed by a concomitant disruption of the initially formed oxetane moiety and an aromatic ring of naphthalene moiety, can be regarded as a novel aromatic Paterno-Buchi reaction.