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Phase-transfer-catalyzed alkylation of glycinate Schiff base with racemic secondary alkyl halides proceeded with excellent levels of synand enantioselectivities under the influence of a chiral quaternary ammonium bromide and 18- crown-6. The alkylation product can be selectively converted to the corresponding anti isomer, allowing the preparation of all the stereoisomers of β-alkyl-α-amino acid derivatives. | Synthesis of a-Amino Acids and Derivatives Related Name Reactions Petasis Reaction Recent Literature Ar I 1 1.1 eq. jPrMgCI NHBoc 3 eq. 0.75 M THF 0 C or r.t. 1 h I HCI in Ether -------------------------- AK-A-CO2Et ------------------ 2 1 eq. C02Et -7S C 1 h Ar q0 g r.t. 12 h BocN 2 C02Et extractive workup NH2 Ar A-COjEt Ar CO.- Et Diethyl A-Boc-iminomalonate. prepared on multi-gram scale served as a stable and highly reactive electrophilic glycine equivalent which reacted with organomagnesium compounds affording substituted aryl N-Boc-aminomalonates. Subsequent hydrolysis produced arylglycines. P. Cali M. Begtrup Synthesis 2002 63-64. Using a cinchonine-derived alkaloid catalyst enantioselective alkylations of N- diphenylmethylene glycine tert-butyl ester were efficiently carried out with various alkyl halides to give products in high enantiomeric excess. W. He Q. Wang Q. Wang B. Zhang X. Sun S. Zhang Synlett 2009 1311-1314. catalyst .2eq CO2 Bu mHÆatalyStK - CO2tElu CQL JOO 1 mol- 18-crown-6 - 2 B r -------------- - I N Br I N CPh toluene 50 KOH R N CPh 3 1 0 C 3.5 - 6 h L L 11 H LB R Ar alkynyl A Q-Ar Ar Ar 315-CFj i H Phase-transfer-catalyzed alkylation of glycinate Schiff base with racemic secondary alkyl halides proceeded with excellent levels of syn-and enantioselectivities under the influence of a chiral quaternary ammonium bromide and 18-crown-6. The alkylation product can be selectively converted to the corresponding anti isomer allowing the preparation of all the stereoisomers of 0-alkyl-a-amino acid derivatives. T. Ooi D. Kato K. Inamura K. Ohmatsu K. Maruoka Org. Lett. 2007 9 3945-3948. 2 eq. Ar B OH 2 0 N .J1--. .-OEt 0 S NH . JL .-OEt 0 5 mol- Rh acac coe 2 5.5 mol- dppbenz dioxane 70 C 1 4 -1 6 h r n coe cyclooctene II dppbenz bis diphenylphosphino benzene 0 dr 98 2 A new method for the Rh I -catalyzed addition of arylboronic acids to chiral .
