| http://www.w3.org/ns/prov#value | - According to step (d) of the process, the reaction between the compounds of formula (V) and (VI) is carried out in the presence of catalytic amounts of a suitable acid such as, for instance, hydrochloric, acetic, sulfuric or p-toluensulfonic acid, and in a solvent such as methanol, ethanol, benzene, toluene or the like.
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