An Unusual Ring Contraction of 7-Methyl-1,7-naphthyridinium and 6-Methyl-1,6-naphthyridinium Salts in Reaction with Liquid Ammonia/Potassium Permanganate

Article abstract of DOI:10.1021/jo00219a002

Treatment of 7-methyl-1,7-naphthyridinium iodide (1) with liquid ammonia/potassium permanganate gives the 8-imino compound 3 and two ring contraction products, which by 1H NMR spectroscopy were assigned as 3-amino-1,3-dihydro-2-methyl-4-azaisoindol-1-one (5) and 1,3-dihydro-2-methyl-4-azaisoindole-1,3-dione (6).The structure of 5 was confirmed by X-ray analysis.Similarly from 6-methyl-1,6-naphthyridinium iodide (2) the 5-imino compound 7 together with 1-amino-1,3-dihydro- (8) and 1-imino-1,3-dihydro-2-methyl-4-azaisoindol-3-one (9) were formed. 1H NMR spectroscopy unequivocally shows that 1 and 2 are converted with ammonia into 8-amino-7,8-dihydro-7-methyl-1,7-naphthyridine (11) and 5-amino-5,6-dihydro-6-methyl-1,6-naphthyridine (12), respectively.The mechanism of the ring contraction is discussed.