Solid state conformations of six 1,3,2-oxazaphospholidines derived from (–)-ephedrine: X-ray crystal structures of the 2-phenoxy-2-oxo, 2-phenyl-2-oxo and 2-phenyl-2-thio analogues

Abstract

The crystal structure of (2R,4S,5R)-3,4-dimethyl-2-phenoxy-5-phenyl-1,3,2-oxazaphospholidin-2-one (7) exhibits a C(5) envelope in which this atom is below the O(1)–P(2)–N(3)–C(4) plane. The diastereoisomer, (2S,4S,5R)8 adopts a half-chair conformation with C(4) above and C(5) below the O(1)–P(2)–N(3) plane. Both (2S,4S,5R)- and (2R,4S,5R)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidin-2-one (9 and 10), and (2S,4S,5R)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidin-2-thione (12) adopt C(4) envelopes in the crystal structures, with C(4) above the C(5)–O(1)–P(2)–N(3) plane for 9 and below for 10 and 12, (2R,4S,5R)-3,4-Dimethyl-2,5-diphenyi-1,3,2-oxazaphospholidine-2-thione (11) exists as a half-chair with O(1) above and C(5) below the P(2)–N(3)–C(4) plane. The C(4) and C(5) envelope conformations for 7, 9, 10 and 12 are consistent with the P–O–C–H vicinal coupling constants derived from ¹H NMR spectra in solution.