Methanesulfonic Acid → Methanesulfonic Acid

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Reaction Steps

In step c, scheme 5, cleavage of the acetal and reductive cyclization of 26 leads to piperazinone 22 (L=a bond, p=0, R8 and R10═H), described as intermediate in scheme 4. This conversion is performed either in one step using an acid, e.g., trifluoroacetic acid or methanesulfonic acid, and a reducing agent such as sodium borohydride or triethylsilane, in solvents such as dichloromethane, 1,4-dioxane, tetrahydrofuran, water, or mixtures thereof. Alternatively, the reaction may be performed in two steps, by first forming a 3,4-dihydro-1H-pyrazin-2-one intermediate in the presence of an acid, e.g., trifluoroacetic acid or methanesulfonic acid, in a solvent such as water or dichloromethane, and subsequent catalytic hydrogenation at pressures between 1 bar and 10 bar, using a suitable catalyst, e.g., palladium on activated charcoal, in solvents such as methanol, ethanol, ethyl acetate, or mixtures thereof, at temperatures between 0° C. and 50° C.

Provenance & Evidence