van Delden Richard A, Hurenkamp Johannes H, Feringa Ben L
Department of Organic and Molecular Inorganic Chemistry, Stratingh Institute, University of Groningen, The Netherlands.
Chemistry. 2003 Jun 16;9(12):2845-53. doi: 10.1002/chem.200204660.
A new type of chiroptical molecular switch is presented where irradiation employing different wavelengths of light induces a reversible helix inversion of a sterically overcrowded alkene bearing a second chiral entity in the form of a stereogenic center present in a pyrrolidine unit. The additional stereogenic center in the chiral auxiliary group has a distinct influence on the switching selectivity of this system and greatly facilitates the resolution of the different diastereoisomers, which is a considerable improvement compared with previously reported systems. In addition, the pyrrolidine stereogenic center causes small energetic differences between the various states of the switch system resulting in a small but significant directional preference in the helix inversion steps.
