A process for synthesis of enatiomerically pure or enatiomerically enriched or racemic mixture of (+and/or−) epicatechin echm and its intermediates, comprising the steps of: (i) obtaining penta-protected quercetin; (ii) reducing the penta-protected quercetin obtained from step (i); (iii) optionally deprotecting the compound of step (ii); (iv) reducing the compound obtained from step (ii) or step (iii) in the presence of a chiral/achiral reducing agent to obtain a chiral intermediate; (v) deprotecting and/or hydrogenation of the chiral intermediate obtained from step (iv) to obtain (−)-epicatechin; (vi) optionally simultaneously deprotecting and by drogenation of the compound obtained from step (ii) to obtain racemic epicatechin.
Crystals of an aromatic 0,0'-diacyltartaric acid of the formula (VIII):
wherein R2 and R3 are the same as or different from one another and each is a hydrogen atom, halogen atom or C1 - C4 alkyl group are sufficiently uniform in size that 95% to 98% of them pass through a 20-mesh sieve. Such crystals may be prepared by hydrolyzing an aromatic carboxylic anhydride of the formula (IV):
wherein R2 and R3 are as defined above, to form the corresponding acid (VIII) in the form of an oil and crystallizing the acid in the presence of an organic solvent which is immiscible with water to form crystals of the hydrate of the acid (VIII). For the crystallization process, each of the organic solvent immiscible with water and seed crystals of the acid (VIII) are added to the oil of the acid (VIII) present in the reaction mixture.