In a previous paper, we reported a new method for the synthesis of N-carboxy-α-amino acid anhydride (NCA) by the use of trichloromethyl chloroformate (TCF). We have examined some detailed reaction conditions for the new method and it was found that (i) more than 1.375 molar amounts of TCF should be added to γ-methyl ester of L-glutamic acid : (ii) water content in the reaction mixture has little influence on the reaction : (iii) the reaction time can not be shorten by passing nitrogen gas through the reaction mixture to drive off hydrogen chloride produced : (iv) irradiation of UV light to the mixture after the completion of the reaction to decompose excess TCF is not effective.
Reaction of cyclic α, β-unsaturated β-amino ketones with thiocyanogen was investigated. 3-Amino-5, 5- dimethy1-2-cyclohexen-1-one (1c) reacted with thiocyanogen in 1, 2-dichloroethane at 20°C to give 2-amino-5, 5-dimethyl-7-oxo-4, 5, 6, 7-tetrahydrobenzothiazole (3c) in 41% yield. The reaction of 3-substituted amino-2-cyclohexen-1-one (1a, b) and 3-substituted amino-5, 5-dimethyl-2-cyclohexen-1-one (1d, e) (substituent R2 : Me and Ph) with thiocyanogen at -5-20°C gave 3-methyl- or 3-phenyl-2-imino-7-oxo-4, 5, 6, 7-tetrahydro-benzothiazoline (4a, b) and 3-methyl- or 3-phenyl-5, 5-dimethyl-2-imino-7-oxo-4, 5, 6, 7-tetrahydrobenzothiazoline (4d, e) in 25-75% yield.