A new model of light-powered chiral molecular motor with higher speed of rotation, part 1 - Synthesis and absolute stereostructure

To develop a molecular motor with a higher speed of rotation, a new model light-powered chiral molecular motor 2 of five-membered ring type was designed, and the motor rotation isomers (-)-2a and (-)-2c were directly synthesized in enantiopure forms for the first time from the ketone (+)-8. The precursor alcohols 9 and 10 were enantioresolved by the camphorsultam-dichlorophthalic acid (CSDP acid; 3) method, and their absolute configurations were determined by X-ray crystallographic analysis of the CSDP ester (-)-11b and chemical correlations. The enantiopure ketone (S)-(+)-8 formed from (1S,2S)-(+)-9 or (1R,2S)-(-)-10 was subjected to the McMurry reaction with TiCl3/LiAlH4, yielding the motor rotation isomers [CD(-)257.8]-(2S,2'S)-(M,M)-(E)-(-)-2a and [CD(-)270.0]-(2S,2'S)-(M,M)-(Z)-(-)-2c. These studies enabled us unambiguously to determine the absolute stereostructure of the motor 2, which is of critical importance for control over the direction of motor rotation. ((c) Wiley-VCH Verlag GmbH & Co, KGaA, 69451 Weinheim, Germany, 2005).