Cycloadditions of 5-Nitropyrimidines with Ynamines. Formation of 3-Nitropyrimidines, N-5-Pyrimidyl-α-carbamoylnitrones, and 2,2a-Dihydroazeto-3,5-diazocines

Article abstract of DOI:10.1021/jo00351a012

The reaction of pyrimidines containing an electron-withdrawing substituent at C5 with ynamines (2) has been investigated. 5-(Ethoxycarbonyl)- and 5-(methylsulfonyl)pyrimidine (1a and 1c) undergo a <4 + 2> cycloaddition to yield the 3,4,5-trisubstituted pyridines 3a and 4, respectively. 5-Nitropyrimidines containing 2- and/or 4(6)-alkoxy or methyl groups (6) give a variety of products upon reaction with 2. 4,6-Dimethoxy-5-nitropyrimidine (6b) gives a <4 + 2> cycloaddition reaction into the pyridine derivative 8a upon reaction with 1-(diethylamino)propyne (2a).Nitrone10a is formed as the main product upon reaction of 2a with 2,4-dimethoxy-5-nitropyrimidine (6c). 5-Nitropyrimidines unsubstituted at position 4 and 6 (6a,e-g) give 2,2a-dihydroazeto<2,3-d>-3,5-diazocines (7a-e) upon reaction with 2 equiv of 2a. 4-Methoxy-5-nitropyrimidine (6d) yields pyridine 8a and nitrone 10b upon reaction with 2a, and from 4-methyl-5-nitropyrimidine (6h), the pyridines 8b and 8c, dihydroazetodiazocine 7e, and a nitrone are formed.Ynamine 2b is less reactive than 2a and does not react to form dihydroazetodiazocines (7) with the 5-nitropyrimidines used in this study.Instead, nitrone 10c and pyridine 11 are formed upon reaction of 2b with 6a, and nitrone 10d is formed with pyrimidine 6g.