A-4- Trifluoromethyl benzyl-cinchoninium Bromide

Solubility 10 M in toluene 20 mM in toluene as dirner. Form Supplied in crystalline salt commercially available. Can contain anywhere from 0 to 25 mol % of the dihydro analog, usually 15 mol %. 

Handling, Storage, and Precautions do not breath dust avoid contact with skin and eyes. 

Asymmetric Alkylation. 7Y-[4-(Trifluoromethyl)benzyl]-cinchoninium bromide (1) has been used as chiral phase-transfer catalyst in the alkylation of indanones (eq 1). For the alkylation of a-aryl-substituted carbonyl compounds the diastere-omeric 7Y-[4-(trifluoromethyl)benzyl]cinchonidinium bromide (2) was used to obtain the opposite stereochemistry (eqs 2 and 3). The asymmetric alkylation of oxindoles was used as the key step in an asymmetric synthesis of (—)-physostigmine (eq 4).  

In all cases it was reported that the trifluoromethyl group enhances the interaction in the prochiral ion pair, resulting in higher ee. The exception appears to be the asymmetric synthesis of a-amino acids via alkylation of the benzophenone Schiff base of glycine alkyl esters with allyl bromide, which produced a 56% ee with the trifluoromethyl-substituted catalyst compared to 66% with the unsubstituted catalysts TY-benzylcinchoninium chloride (3) or TY-benzylcinchonidinium chloride (4) (eq 5).  

The unsubstituted catalyst (3) was also used in an asymmetric Gabriel synthesis of a-amino acids via solid-liquid chiral phase-transfer alkylation of potassium phthalimide with 2-bromocarboxylates.  

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