Abstract
Small amounts of MoO2Cl2 or MoO2Cl2(DMF)2 catalyze carbamate
formation from an alcohol and isocyanates: 0.1 mol% of the
respective additive allow primary, secondary or tertiary alcohols to
add to aliphatic or aromatic isocyanates of varied steric hindrance within
20 minutes at room temperature. Typically the corresponding carbamate
resulted in 100% yield. Only particularly hindered substrates
required 1.0 mol% of the catalyst while as little as 0.01% sufficed
for the phenylcarbamoylation of menthol. Catalytic amounts of DMAP
accelerate carbamate formation from certain alcohols and isocyanates,
too.
Key words
addition - carbamoylation - DMAP - heterocumulene - urethane formation
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Typical Procedure
for the Carbamoylation of Alcohols with Isocyanates: At 22 ˚C
neat benzyl isocyanate (31; 0.52 mL, 0.56
g, 1.1 equiv) was added to MoO2Cl2(DMF)2 (1.3 mg,
3.8 µmol, 0.1 mol%) and 1.0 M (-)-menthol
(16; 594 mg, 3.80 mmol) in CH2Cl2 (3.8
mL). The mixture was stirred at r.t. for 20 min. CH2Cl2 (10
mL) and H2O (7 mL) were added. The aqueous phase was
extracted with CH2Cl2 (2 × 12 mL).
The combined organic phases were dried over Na2SO4.
Removal of the solvent under reduced pressure gave N-benzyl-O-[(1R,2S,5R)-2-isopropyl-5-methylcyclo-hexyl] carbamate (35;
1.10 g, 100%) as a white solid (mp 92 ˚C). It
was a pure compound as evidenced by ¹H NMR spectroscopy
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Carbamates 12, 15, 36, and 37 are
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All new compounds (12, 15, 36, and 37) gave satisfactory ¹H NMR
and ¹³C NMR spectra and correct combustion
analyses for C, H, and N (±0.30%). Analytical
details will be published in a full paper in due course.