NOVELTY - In-situ preparation of 3-(carbamoylmethyl)-5-methylhexanoic acid involves: (a) reacting isovaleraldehye and cyanoacetamide to obtain a reaction mass containing intermediate; (b) treating the obtained reaction mass with mineral acid; (c) extracting the reaction mass from (b) with a suitable solvent to obtain an organic layer containing 3-isobutylglutaric acid; (d) concentrating the organic layer to obtain residue; (e) treating the residue with urea to obtain imide intermediate; and (f) carrying out the hydrolysis of imide intermediate to obtain 3-(carbamoylmethyl)-5-methylhexanoic acid.    USE - The process is useful for in-situ preparation of 3-(carbamoylmethyl)-5-methylhexanoic acid (II) used in preparing Pregabalin (I) (claimed).    ADVANTAGE - The process is simple, economical, eco-friendly, and easily scalable. Also, the process has shorter reaction time, improved yield, and uses small volumes of solvent.    DETAILED DESCRIPTION - In-situ preparation of 3-(carbamoylmethyl)-5-methylhexanoic acid of formula (II) involves: (a) reacting isovaleraldehye and cyanoacetamide in the presence of catalytic amount of inorganic base to obtain a reaction mass containing intermediate of formula (V); (b) treating the reaction mass obtained in step (a) with mineral acid to obtain 3-isobutylglutaric acid of formula (IV); (c) extracting the reaction mass obtained in step (b) with a suitable solvent to obtain an organic layer containing 3-isobutylglutaric acid of formula (IV); (d) concentrating the organic layer to obtain residue; (e) treating the residue obtained in step (c) with urea to obtain imide intermediate of formula (III); and (f) carrying out the hydrolysis of imide intermediate to obtain 3-(carbamoylmethyl)-5-methylhexanoic acidStructures II, III, IV and V, pages 15-16, (claim 1) INDEPENDENT CLAIMS are included for:    (1) in-situ preparation of 3-isobutylglutaric acid (IV), which involves: (a) reacting isovaleraldehye and cyanoacetamide in the presence of catalytic amount of inorganic base to obtain a reaction mass containing intermediate of formula (V); (b) treating the reaction mass obtained in step (a) with mineral acid to obtain 3-isobutylglutaric acid (IV); (c) extracting the reaction mass obtained in step (b) with an suitable solvent to obtain an organic layer containing 3-isobutylglutaric acid (IV); and (d) isolating 3-isobutylglutaric acid (IV); and    (2) preparation of Pregabalin of formula (I) using 3-(carbamoylmethyl)-5-methylhexanoic acid (II) or 3-isobutylglutaric acid (IV).    .