Base-Catalyzed Transcarbamoylation

Abstract

Inorganic bases such as NaH, KOt-Bu, NaOH, or KOH are efficient catalysts to promote the transcarbamoylation reaction between urethanes and a variety of primary and secondary alcohols under mild conditions. They constitute an alternative to organometallic catalysis and can be applied to aliphatic or aromatic urethanes.

Key words

urethane - carbamate - transcarbamoylation - transurethanisation - base

• References and Notes

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• 26 General Procedure for Transcarbamoylation In a 25 mL round-bottom flask, the urethane (0.66 mmol) was dissolved in dry toluene (2 mL). The alcohol (3 equiv, 1.98 mmol) and the base (1.2 equiv, 0.79 mmol) were added, and the reaction mixture was heated at 60 °C with continuous agitation. Samples were taken at regular time intervals and analyzed by HPLC and ¹H NMR spectroscopy to estimate conversion. To isolate the pure product, water (10 mL) and EtOAc (10 mL) were added to the reaction mixture. The organic layer was separated, dried over MgSO₄, filtered, and the solvent was evaporated. The residue was purified by silica column chromatography eluting with a 10–50% EtOAc–cyclohexane gradient. The fractions were concentrated under reduced pressure to give the desired product. Butyl N-Phenylcarbamate White solid (115 mg, 90% yield). HPLC: t _R = 16.1 min (linear gradient, 0–60% B, 20 min). ¹H NMR (300 MHz, DMSO-d ₆): δ = 9.57 (s, 1 H), 7.43 (d, J = 7.5 Hz, 2 H), 7.24 (t, J = 7.5 Hz, 2 H), 6.95 (t, J = 6 Hz, 1 H), 4.05 (t, J = 6.8 Hz, 2 H), 1.46–1.72 (m, 2 H), 1.23–1.46 (m, 2 H), 0.89 (t, J = 7.3 Hz, 3 H) ppm. Octyl N-Phenylcarbamate White solid (135 mg, 82% yield). HPLC: t _R = 18.9 min (linear gradient, 0–60% B, 20 min). ¹H NMR (300 MHz, CDCl₃): δ = 7.38 (d, J = 7.5 Hz, 2 H), 7.31 (t, J = 7.5 Hz, 2 H), 7.06 (t, J = 7.5 Hz, 1 H), 7.06 (br s, 1 H), 4.16 (t, J = 6.8 Hz, 2 H), 1.59–1.76 (m, 2 H), 1.12–1.45 (m, 10 H), 0.79–0.89 (m, 3 H) ppm. 2-Methoxyethyl N-Phenylcarbamate White solid (120 mg, 93% yield). HPLC: t _R = 14.5 min (linear gradient, 0–60% B, 20 min).¹H NMR (300 MHz, CDCl₃): δ = 7.22–7.49 (m, 4 H), 6.99–7.12 (m, 1 H), 6.64–6.83 (m, 1 H), 4.33 (t, J = 4.5 Hz, 2 H), 3.65 (t, J = 4.5 Hz, 2 H), 3.42 (s, 3 H).