Phosgene → 2-(1-Tert-butoxycarbonyl-indol-3-yl)-2-oxo-ethylisocyanate

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Reaction Steps

To a stirred solution of 3-aminoacetyl-1-(tert-butoxycarbonyl)-indole, which may be prepared as described in Step (e) above, (0.01 mol), optionally in the presence of from 1 to 3 mol equivalents of a volatile (i.e., boiling point <150° C.) non-nucleophilic base such as, for example, a volatile tertiary organic amine or pyridine, or a solid non-nucleophilic base such as, for example, sodium hydride, or 3-aminoacetyl-1-(tert-butoxycarbonyl)-indole hydrochloride, which may be prepared as described in Step (e) above, (0.01 mol), optionally in the presence of from 2 to 4 mol equivalents of said non-nucleophilic bases, in a solvent such as dichloromethane or ethyl acetate, is stirred. A suitable reagent such as, for example, 1 mol equivalent of phosgene or 0.33 mol equivalents of triphosgene is added. After stirring for from 10 minutes to about 24 hours, the mixture is diluted with up to an equal volume of a diluent such as diethyl ether or ethyl acetate (preferred diluent is diethyl ether), and any precipitates are filtered off. The filter cake is washed with additional diluent. The filtrate and washings are combined and rotary evaporated to give 2-(1-tert-butoxycarbonyl-indol-3-yl)-2-oxo-ethylisocyanate, which may be purified, if needed or desired, by vacuum distillation.

Provenance & Evidence