The (dl) a-keto esters 16, were prepared from the (dl) carbinols 1 to and from (dl) -2-hydroxyheptaElicene 5. These (dl) a-keto esters underwent NaBHq reductions to give the corresponding diastereomeric (dl) a-hydroxy esters 11, with 54 to -100% diastereaneric excesses.Highly enantioselective and/or diastereoselective syntheses are of great importance in organic chemistry. As an ultimate goal we aimed at the preparation and use o f chiral secondary alcohols and phenolewhich could lead to highly effective asymmetric inductions.process to evaluate the steric approach control as it is easy to modulate the bulkyness of the alkoxy moety of the ester '.available2'3 and proved to be efficient inducers in the reduction of the corresponding a-keto esters with NaBH4.The NaBH' reduction of a-keto esters was considered to be an efficient We have studied four secondary (dl) alcohols (1 to i) which are readily

SUMMARYAtrolactic syntheses have been carried out to evaluate the potentiality, in asymmetric syntheses, of chiral inducers. The (d1)-hydroxyhelicenes l, 2, the (dl) sec. alcohols 1-12 and the (d1)phenolic binaphtyl compound have been used as inducers. The d.e. are collected in table I (6-100%). The atrolactic asymmetric synthesis has also been carried out using three optically active inducers, namely : (-)-quinine 13, (-)-l0,ll-dihydroquinine -14, and R(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol 5. Diastereomeric and enantiomeric excesses equal or greater than 88% have been obtained in six cases out of sixteen :(l-naphtyl)-(9-anthryl)methanol 3 (d.e = 90%) ; 2,2,2-trichloro-1-(9-anthryl) ethanol 7 (d.e = 100% ?2), 2,2,2-tribromo-1-(9-anthryl)ethanol 8 (d.e = 100% +2), (-)=quinine 13 (e.e = 95.5%), and (-)-2,2,2-trifluoro-l-(9-anthryl) ethanol 6 (e.e = 88%).

Dedie a la memoire de Nicole Defay, Dr. Sc.

Keywords: Helicenes / Heck reaction / Palladium / Photocyclisation / Synthetic methods 2-Bromo[5]helicene derivatives and substituted [7]helicenes have been prepared through a synthetic sequence relying on Heck-type and photocyclodehydrogenation reactions. This procedure provides a new, versatile and efficient approach to helicene derivatives.