The Schiff base (I) from glycine tert-butyl ester and benzaldehyde was treated with lithium diisopropylamide to give the corresponding α-carbanion. Alkylation of the α-carbanion with benzyl or butyl halide followed by removal of benzylidene group yielded phenylalanine or norleucine tert-butyl ester (IIa or IIb), accompanied by dialkylated product (IIIa or IIIb). The Schiff base (IV) from alanine tert-butyl ester and (-)-men-thone (VI) was also treated as above to furnish α-methylphenylalanine or α-methyl-β-(3, 4-dimethoxyphenyl) alanine tert-butyl ester (Va or Vb) in 21 or 24% asymmetric yield.
从
甘氨酸叔丁酯和
苯甲醛反应得到的希夫碱(I)用
二异丙基铵锂处理,生成相应的α-碳负离子。用苄基或丁基卤化物对α-碳负离子进行烷基化反应,并去除苄亚基,生成苯丙
氨酸或去甲
硫氨酸叔丁酯(IIa或IIb),同时伴有双烷基化产物(IIIa或IIIb)。由丙
氨酸叔丁酯和(-)-
薄荷酮(VI)反应得到的希夫碱(IV)也经过上述处理,获得α-甲基苯丙
氨酸或α-甲基-β-(3, 4-二
甲氧基苯基)丙
氨酸叔丁酯(Va或Vb),其不对称产率分别为21%或24%。