FIRST X-RAY DETERMINATION OF AN OXAZIRIDINIUM SALT - (1S,2R,3R,4S)-2,3-DIMETHYL-4-PHENYL-1,2,3,4-TETRAHYDRO-1,2-EPOXYISOQUINOLINIUM TETRAFLUOROBORATE AND (1S,2R,3R,4S)-3-METHYL-4-PHENYL-1,2,3,4-TETRAHYDRO-2,3-EPOXYISOQUINOLINE

The chiral oxaziridinium salt (1), (CHNO+)-H-17-N-18.BF4-, transfers the O atom enantioselectively to nucleophilic substrates. The configuration (1S,2R) for the O atom has been established. This is the first X-ray determination for an oxaziridinium salt. Its geometry is quite superimposable with that of the parent oxaziridine (2), C16H15NO. The N-O bond length of 1.468(8)Angstrom in the oxaziridinium salt is shortened compared with the mean bond length of 1.508 (16) Angstrom observed in 40 X-ray structures of oxaziridine. The oxaziridine ring is perpendicular to the isoquinoline ring, the former making a dihedral angle of 97 degrees with the mean plane of the latter in (1), and dihedral angles of 94 and 93 degrees in the two independent molecules of (2).