The present invention relates to an improved process for the prepn. of dihydrothieno[3,2-d]pyrimidine diols I [R1, R2 = H, alkyl, cycloalkyl, aryl, etc.] and similar pyrimidine diols such as II [R3, R4 = H, alkyl, cycloalkyl, aryl, etc.; or R3 and R4 are combined with the carbon atoms to which they are attached to form (un)substituted benzene, pyridine, pyrimidine, etc.; R5 = H, alkyl, cyclolkyl, aryl, etc.], that is efficient, high-yielding, and does not require expensive and potentially unstable intermediates. Compds. I were prepd. by reacting compd. III [R1 and R2 are defined as above; R = H, halo, alkyl, aryl] with urea in the presence of acid followed by cyclizing the resulting intermediate IV [R, R1, R2 are defined as above] with a base. For example, reacting III [R1, R2 = H; R = Me] with urea in the presence of conc. HCl in MeOH followed by treating intermediate IV [R1, R2 = H; R = Me] with NaOH afforded I [R1, R2 = H]. The diols are used as intermediates in the synthesis of pyrimidine compds. which inhibit PDE4, and are thus useful in the treatment of respiratory or gastrointestinal diseases and complaints, peripheral or central nervous system diseases and disorders, inflammatory conditions, and cancers.
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