Formation and Reactions of Dewar 4-Pyrimidinones in the Photochemistry of 4-Pyrimidinones at Low Temperature. 2

Article abstract of DOI:10.1021/jo00165a025

The photochemistry of the 4-pyrimidinones 1b-l in liquid NH3-ether solution at -40 deg C or in methanol at -10 to -40 deg C was studied.Irradiation of 1b-g at low temperature gave the corresponding Dewar 4-pyrimidinones (2b-g), whose physical properties (IR, NMR, and UV) were determined.The photolysis of 1h-j in methanol at -10 to -20 deg C gave methanol adducts 5-7 which suggested the formation of the Dewar 4-pyrimidinones 2h-j.However, the intermediate 2h could not be detected in liquid NH3-ether solution at -40 deg C.The hydrogen of the amino group increases sharply the reactivity of 2h-j.Irradiation of 1k and 1l in liquid NH3-ether solution at -40 deg C gave the crystalline product 3 and inseparable products, respectively, which did not suggest the formation of 2k and 2l.Presumably, the excited 4-pyrimidinone 1k directly reacts with ammonia before electrocyclization.The 4-pyrimidinone 1l may decompose by excitation.The reactions of the Dewar 4-pyrimidinones 2a-j in methanol and in methanol containing sodium methoxide were studied.The products were the β-lactam 4, imino ether 5, and acetals 6-8.The Dewar 4-pyrimidinones 2e-g gave inseparable products and two unidentified products in methanol, respectively.