2-Amino-3-chloropyrazine → 8-Chloro-3-(2-methylsulfanyl-pyrimidin-4-yl)-imidazo[1,2-a]pyrazine

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Reaction Steps

Alternatively, intermediate 7 used in the synthesis of compounds of formula Ia can be prepared according to Schemes 2-4 below. 2-Methylsulfanyl-pyrimidine-4-carbaldehyde (8) can be condensed with (methoxymethyl)triphenylphosphonium chloride (Wittig reaction) to give 4-(2-methoxy-vinyl)-2-methylsulfanyl-pyrimidine (9). Oxidation of (9) with N-bromosuccinimide in methanol provides 4-(1-bromo-2,2-dimethoxy-ethyl)-2-methylsulfanyl-pyrimidine (10). Condensation of (10) with 2-amino-3-chloropyrazine (1) in aqueous acid and a co-solvent such as acetone gives 8-chloro-3-(2-methylsulfanyl-pyrimidin-4-yl)-imidazo[1,2-a]pyrazine (11). Compound 11 can then be reacted with an appropriate amine (HNR1R2) either in excess or in the presence of another base, such as diisopropyl ethyl amine, in an appropriate solvent, such as ethanol or butanol, between room temperature to reflux to give the intermediate 7. Intermediate 7 can also be prepared via the ethyl homologs 9′ and 10′ according to Scheme 4 below. Compound 9′ (the ethyl homolog) can be prepared by the reaction ethyl ethynyl ether (13) with borane—tetrahydrofuran complex followed by palladium catalyzed coupling with 4-chloro-2-(methylthio)pyrimidine (12). Oxidation of 9′ with N-bromosuccinimide in ethanol provides the ethyl homolog 10′. Homolog 10′ can be converted to intermediate 7 in the same way as 10.

Provenance & Evidence