Alkyl biphenyl carboxylates, synthesis

An enantioselective synthesis of both (R)- and (5)-a-alkylcysteines 144 and 147 is based on the phase-transfer catalytic alkylation of fert-butyl esters of 2-phenyl-2-thiazoline-4-carboxylic acid and 2-ort/ro-biphenyl-2-thiazoline-4-carboxylic acid, 142 and 145 <06JOC8276>. Treatment of 142 and 145 with alkyl halides and potassium hydroxide in the presence of chiral catalysts 140 and 141 gives the alkylated products, which are hydrolyzed to (R)- and (S)-a-alkylcysteines 144 and 147, respectively, in high enantioselectivity. This method may have potential for the practical synthesis of chiral a-alkylcysteines. 

Other examples of shown effectiveness of PTCs were reported by Park, Jew, and co-workers [98], They developed enantioselective synthetic method for the preparation of (/ )-a-alkylserines and (S)-a-alkylserines based on asymmetric alkylation of phenyl or o-biphenyl oxazoUne derivatives using CBPTC XXXXVIa and binaphthol-derived Maruoka s catalyst XXV, respectively (Scheme 8.16). The same authors [99] also expanded this methodology to enantioselective synthesis of (/ )-a-alkylcysteines and (5)-a-alkylcysteines using thiazoline-4-carboxylates in PTC alkylation. In 2006, Maruoka and co-workers [100] reported first example of the catalytic asymmetric alkylation of glycolates that establishes stereogenic quaternary carbon centers (Scheme 8.17). Their approach utilized 3,5-diaryloxazolidin-2,4-diones 48 as novel... 

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