(S)-6-Chloro-4-cyclopropylethynyl-4-trifluoromethyl-1H-3,1-benzoxazin-2(4H)-one

• Main Authors: James L. Wardell, Edward R. T. Tiekink, R. Alan Howie, Silvia Cuffini, Solange M. S. V. Wardell
• Format: Article
• Language: English
• Published: International Union of Crystallography 2009-12-01
• Series: Acta Crystallographica Section E
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S1600536809049101

Two independent molecules comprise the crystallographic asymmetric unit in the title antiretroviral agent Efavirenz, C14H9ClF3NO2, and these have noteworthy differences in conformation. The major difference relates to the orientation of the 2-cyclopropylethynyl residue relative to the six-membered heterocycle: this approaches an orthogonal disposition in molecule a compared to a more flattened conformation in molecule b, the difference being reflected in the Oring—C—C—Cethyne torsion angles of 65 (4) and 159 (5)°, respectively. The independent molecules are connected via the eight-membered {...HNC (O)}2 amide synthon. Disorder is noted in the cyclopropane ring of molecule b in that two orientations of equal weight were discerned.