... Chem. 1975, 12, 1051-1052. (17) See Fleming, I. In Comprehensiue Organic Chemistry; Barton, DH 102, 5835-5838. 3076-3084. ... 3, p 576. 0 1989 American Chemical Society Page 2. Tautomerism of Five- Membered Heterocycles J. Am. Chem. Soc., Vol. 111, No. 14, 1989 5347 ...