Cl[C:2]([O:4][CH2:5][CH:6]([CH3:8])[CH3:7])=[O:3].[NH2:9][C:10]1[C:15]([O:16][CH3:17])=[N:14][C:13]([Cl:18])=[CH:12][N:11]=1.N1C=CC=CC=1.Cl>ClCCl>[Cl:18][C:13]1[N:14]=[C:15]([O:16][CH3:17])[C:10]([NH:9][C:2](=[O:3])[O:4][CH2:5][CH:6]([CH3:8])[CH3:7])=[N:11][CH:12]=1
Isobutyl chloroformate (4.1 g) was added to a solution of 2-amino-5-chloro-3-methoxypyrazine (4.8 g) and pyridine (2.37 g) in dichloromethane (50 ml). The solution was left to stand for 20 hours and then two further portions of isobutyl chloroformate (1.02 g) and pyridine (0.59 g) were added at 2 hour intervals. 2M hydrochloric acid (25 ml) was added and the organic layer was separated. The solution was washed with 2M hydrochloric acid (2×25 ml), water (25 ml) and saturated sodium chloride solution (25 ml) The solution was dried (MgSO4) and volatile material was removed by evaporation. The residue was recrystallised from isohexane to give isobutyl N-(5-chloro-3-methoxypyrazin-2-yl)carbamate (6.15 g), m.p. 90°-91° C.; microanalysis found: C, 46.3; H, 5.5; N, 16.4%; C10H14C1N3O3 requires: C, 46.3; H, 5.4; N, 16.2%.
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