(R)-Tert-butyl(1-((1-(3,5-bis(trifluoromethyl)benzyl)-2,5-dioxo-2,3,4,5-tetrahydro-1H-benzo[b]azepin-3-yl)carbamoyl)cyclopropyl)carbamate is used as a reagent in the synthesis of azepinone derivatives as diacylglycerol acyltransferase 1 (DGAT1) inhibitors useful in the treatment of diseases.