On the tautomerism and conformational characteristics of 2-phenylimino-3,1-perhydrobenzoxazines and analogous benzothiazines: an X-ray study

Abstract

The structures of four related 2-phenylimino-3,1-perhydrobenzoxazines and analogous benzothiazines have been established by X-ray crystallography from diffractometer data. Crystals of compound I (C 14H 18N 2O) are triclinic, space group P 1 , with a = 5.634(1), b = 9.932(3), c = 23.742(5) Å, α = 79.40(2), β = 89.84(2), γ = 105.91(2)°, Z = 4 (two molecules in the asymmetric unit) and D c = 1.22 g cm −3. Crystals of II (C 15H 20N 2O) are triclinic, space group P 1 , with a = 8.750(1), b = 12.318(1), c = 13.061(1) Å, α = 99.25(1), β = 81.22(1), γ = 100.98(1)°, Z = 4 (two molecules in the asymmetric unit) and D c = 1.20 g cm −3. Crystals of III (C 14H 18N 2S) are monoclinic, with a = 11.192(1), b = 10.748(2), c = 11.282(2) Å, β = 109.30(1)°, Z = 4 and D c = 1.28 g cm −3. Crystals of IV (C 15H 20N 2S) are also monoclinic with a = 6.306(1), b = 10.008(1), c = 22.033(3) Å, β = 94.94(1)°, Z = 4 and D c = 1.25 g cm −3. The structures were refined to R = 0.065 for 3298 reflections of I, R = 0.046 for 3772 reflections of II, R = 0.056 for 2050 reflections of III, and R = 0.046 for 2337 reflections of IV. The imino form was established for each structure, together with a predominantly E-envelope conformation of the hetero ring. The bulky N3-methyl group in II and IV alters the orientation of N3 relative to the cyclohexane ring from axial to equatorial.