Water → methyl (3R)-5-hydroxy-3-methylpentanoate

To 114 g. of 3-(R)-methylglutaric acid mono methyl ester in 715 ml. of dry tetrahydrofuran cooled to 0° C. was added slowly 391 ml. of 2M solution of borane dimethylsulfide in tetrahydrofuran. After the addition was complete the reaction mixture was stirred overnight at room temperature. The reaction was cooled and 50 ml. of water slowly added. The reaction was extracted (3×100 ml.) with ether and the extracts combined, washed with water, a saturated sodium bicarbonate solution and a brine solution, and dried over magnesium sulfate. Removal of the solvent gave 37 g. of the desired product.