N-benzylcinchoninium salt

Scheme 49 Reagents and conditions i) 50% NaOH, toluene and CH2C12,5°C N-benzylcinchoninium salt.

The enantioselective desymmetrization of prochiral ketones of the type 46 by means of the Horner-Wadsworth-Emmons reaction is an elegant approach to the synthesis of the enantioenriched enone products 47. Enones such as 47 bearing a remote stereogenic center are difficult to prepare by other methods. The first catalytic asymmetric Horner-Wadsworth-Emmons reaction was realized by using cinchona-based PTCs as organocatalysts [40]. Up to 55-57% ee values and satisfactory yields were obtained using catalytic amounts (20 mol%) of the N-benzylcinchoninium salts 48 and RbOH as a base (Scheme 11.25). 

The Wichterle reagent has also been employed in enantioselective Robinson annulations involving the use of phase-transfer catalysis (PTC). Bhattacharya and co-workers had previously investigated the asymmetric alkylation of inadanones, such as 59, using substituted N-benzylcinchoninium salts realizing their ability to produce enantio-enriched... 

---