Synthèse De 3-[Di(Alkylthio) MÉthylène] Nopinones Chirales. Dichroïsme Circulaire: Une Anomalie À La RèGle De l'HéLicité. Structure Cristalline De La (1R,5R)-( )-3-(1',3'-Dithiane-2'-Ylidène) Nopinone

Some chiral 3-[di(alkylthio)methylene] nopinones have been synthetized from (+)-nopinone by action of carbon disulfide, then alkyl halides in basic media and the molecule structure of one of these compounds was carried out by single crystal X-Ray diffraction methods. Crystals belong to space group P2(1) with a = 7.2330 (13), b = 7.872 (7), c = 11.8897 (11) Angstrom, beta = 106.650 (8)degrees, Z = 2, M = 254.39, D-c = 1.303 g.cm(-3), mu = 3.523 mm(-1), F (000) = 272. Circular dichroism of the pi --> pi(*) transition of these compounds is positive and opposite to those of the other alpha,beta-ethylenic derivatives of the nopinone. The presence of the two sulfur atoms and the distorsion of the whole conjugated system shown by the XR study could be responsible for this apparent anomaly.