US Patent 9593119 Process for the preparation of dipeptidylpeptidase inhibitors

The present invention provides a process for the preparation of linagliptin, a compound of Formula I, the process comprising deprotecting a compound of Formula II wherein R1 and R2 together with the nitrogen to which they are attached form a phthalimido group, wherein the aromatic ring of the phthalimido group is substituted with one or more R3 substituents selected from the group consisting of halogen, alkyl, nitro and amino; or R1 is H and R2 is selected from the group consisting of trialkylsilyl, 2-trialkylsilylethoxycarbamates, acetyl, trihaloacetyl, 9-fluorenylmethoxycarbonyl, trityl, alkylsulfonyl, arylsulfonyl, diphenylphosphine and sulfonylethoxycarbonyl.