NOVELTY - Preparation (P1) of (R)-tert-butyl-4-oxo-4-(3-(trifluoromethyl)-5,6-dihydro-(1,2,4)-triazolo(4,3-a)pyrazin-7(8H)-yl)-1-(2,4,5-trifluorophenyl)butan-2-yl-carbamate (IV) or its salt involves: a) condensing 3-tert-butoxycarbonylamino-4-(2,4,5-trifluorophenyl) butyric acid with 3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a) pyrazine or its salt in presence of boronic acid based catalyst to obtain compound (IV).    USE - For preparation of (R)-tert-butyl-4-oxo-4-(3-(trifluoromethyl)-5,6-dihydro-(1,2,4)-triazolo(4,3-a)pyrazin-7(8H)-yl)-1-(2,4,5-trifluorophenyl)butan-2-yl-carbamate (IV) or its salt which is used as intermediate for preparation of sitagliptin (claimed) for treating diabetes (e.g. type 2 diabetes), obesity and high blood pressure.    ADVANTAGE - The present process provides industrially feasible, less hazardous and more eco-friendly process, which at the same time provides improved yield and chemical purity, as well as improved optical purity. The boronic acid based catalyst employed in the process is inexpensive and commercially available. The catalyst is a green catalyst, so it is environmentally friendly. By virtue of the simplicity of the process, the operation is easy to conduct. Therefore, it is amenable for large-scale preparations. The boronic acid based catalyst in the coupling reaction of acid and amine in generating an active ester suitable for amidation in a waste-free catalytic manner.    DETAILED DESCRIPTION - Preparation (P1) of (R)-tert-butyl-4-oxo-4-(3-(trifluoromethyl)-5,6-dihydro-(1,2,4)-triazolo(4,3-a)pyrazin-7(8H)-yl)-1-(2,4,5-trifluorophenyl)butan-2-yl-carbamate of formula (IV) or its salt involves: a) condensing 3-tert-butoxycarbonylamino-4-(2,4,5-trifluorophenyl) butyric acid of formula (II) with 3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a) pyrazine of formula (III) or its salt in presence of boronic acid based catalyst of formula X-B-(OH)2 to obtain compound (IV).    X=hydroxy, straight chain or branched optionally substituted 1-5C alkyl, optionally substituted non-aromatic or aromatic 6-13C aryl, or optionally substituted heterocyclic ring having one to four heteroatoms selected from O, S and N.    An INDEPENDENT CLAIM is included for compound (IV) prepared by the process (P1).