New examples of memory of chirality in fluorenyl ligands gem-substituted by alcohol side arms. Coordination to Cr(CO)3 or CpTiCl metal fragments

The nucleophylic addition of lithium fluorenyl to an excess of racemic propylene oxide forms bifunctionalized fluorenes (80%). The mixture presents substantial diasteromeric selection with enhancement of the racemic (R,R or S,S) with respect to meso form (R,S) (2.6 : 1). This effect can be ascribed to the identification of the preferred chiral conformation in the intermediate step (scheme 1). The resulting species, having memory of chirality (1) of the first-tethered side arm, adds preferentially the second having homochiral conformation. Spectroscopic features and X-ray crystal structure determination of the racemic, meso and enantiopure forms of 1 will be discussed. The reaction with Cr(CO)3(NCMe)3 and molecular grafting to TiCpCl3 will be also reported. (1). Zhao H.; Hsu D.C.; Carlier P.R. Synthesis 2005, 1, 1-16; J. Gawroński J.; Gawrońska K.; Kwit M.; Kacprzak K.; Rychlewska U. Chirality 2004, 16, 405-413.