A mixture of 5-(3,3-dimethyl-but-1-ynyl)-3-[(3-hydroxy-1-(S)-methyl-propyl)-(trans-4-methyl-cyclohexanecarbonyl)-amino]-thiophene-2-carboxylic acid TFA salt (1.40 g, 3.23 mmol) in THF (30 mL) was cooled to 0° C. and triphenylphosphine (2.53 g, 9.69 mmol) was added followed by phthalimide (0.713 g, 4.84 mmol). The reaction was stirred until homogenious then DIAD (1.06 mL, 5.49 mmol) was added. After warming to rt., the reaction was determined to be complete by LC/MS in 1 h. The reaction was quenched with CH3OH (1.0 mL) and the solvent removed under reduced pressure. 5-(3,3-Dimethyl-but-1-ynyl)-3-[[3-(1,3-dioxo-1,3-dihydro-isoindole-2-yl)-1-(S)-methyl propyl]-(trans-4-methyl-cyclohexylcarbonyl)-amino]-thiophene-2-carboxylic acid methyl ester (1.67 g, 92%) was isolated by silica gel chromatography as an off-white solid.
