(5S)-2-(tert-Butoxycarbonyl)-5-[(tert-butoxycarbonyl)amino]-2-(4-hydroxybenzyl)hexanedioic acid 6-tert-butyl ester → Di-tert-butyl (2S)-2-[(tert-butoxycarbonyl)amino]-5-(4-hydroxybenzyl)hexanedioate

Participants

Reaction Steps

A solution of 730 mg (5S)-2-(tert-butoxycarbonyl)-5-[(tert-butoxycarbonyl)amino]-2-(4-hydroxybenzyl)hexanedioic acid 6-tert-butyl ester (1.39 mmol) and 290 mg 4-N,N-dimethylaminopyridine (2.37 mmol) in tetrahydrofuran (10 mL) was heated under reflux for 18 hours. Since the turnover was only approx. 75% then, and to drive the reaction to completion, the mixture was evaporated, the residue dissolved in 1,4-dioxane, and heated under reflux for another 2 hours after which turnover was complete. The mixture was evaporated and the residue was purified by column chromatography on silica gel (2.5→35% ethyl acetate in hexane), to give 590 mg (88% yield) of the target compound featuring an HNMR spectrum in line with the HNMR data for example 12d.

Provenance & Evidence