Carbamate group protecting amines with

A,r-Benzyl groups can be removed by reaction of amines with chloroformates. This can be a useful method for protecting-group manipulation if the resulting carbamate is also easily cleaved. A particularly effective reagent is a-chloroethyl chloroformate, which can be removed by subsequent solvolysis.78... 

Carbamates have mainly been used in solid-phase synthesis as linkers and protective groups for amines (see Sections 3.6.2 and 10.1.10.1). Carbamates are generally prepared by treating amines with aryl carbonates or chloroformates, which can be prepared from alcohols and phosgene or synthetic equivalents thereof. The alternative route, in which carbamates, isocyanates, or carbamoyl chlorides are reacted with alcohols, is less widely used, but can also lead to satisfactory results on insoluble supports (Tables 14.7 and 14.8). 

More versatile are the lithiations of carbamates (N-Boc amines) - as with lithiation a to oxygen, the lack of electrophilicity in a carbamate C=0 group and its particularly electron-rich oxygen lone pairs conspire to facilitate lithiation. In their Boc protected form, even simple amines such as 45 may be lithiated.37... 

Koizumi and co-workers used the optically active allylic chloroselenuranes bearing the 2-exo-hydroxyl-10-bornyl group to obtain optically active allylic amines [41]. The treatment of allylic selenides with f-BuOCl gave the corresponding allylic chloroselenuranes as the only product. Benzyl carbamate, t-butyl carbamate, p-tosylamide, and diphenylphosphinamide were selected as the AT-protected amines for selenimide formation. The nucleophilic reaction of... 

Alkyldithio carbamates are prepared from the acid chloride (EtsN, EtOAc, 0°C) and amino acid, either free or as the O-silyl derivatives (70-88% yield). They may also be prepared by the addition of carbon disulfide to the amine which can then be alkylated with an alkyl halide using CS2CO2 as the base. The A-(i-propyldithio) carbamate has been used in the protection of proline during peptide synthesis. Alkyldithio carbamates can be cleaved with thiols, NaOH, PhsP/TsOH. They are stable to acid. Cleavage rates are a function of the size of the alkyl group as illustrated in the table below. 

This group was developed as a water soluble carbamate in peptide synthesis. It is prepared hy methylating (2-phenylthio)ethylcarbamates of amino acids with methyl iodide and AgBp4. Amines may also be protected using Pms-4-nitrophenyl carbonate as a stable crystalline reagent that can be stored. The Pms group was cleavable with NaHCOi, hut Na2C03 was proved to be more efficient. ... 

On the other hand, catalytic hydrogenation of 121 followed by protection of the resulting amine with p-methoxybenzyl S-(4,6-dimethylpyrimidin-2-yl)thiocarbonate afforded the carbamate 124, which underwent desilylation with TBAF followed by Swem oxidation of the resulting primary hydroxyl group to provide the aldehyde 125. Removal of the protecting groups from 125 with aqueous sulfurous acid at room temperature provided... 

Carbamates are one of the most widely used protecting groups for amines and the development of one-pot conversions of azides to carbamates such as Boc, Cbz, and allyl further expanded the scope of utility of the Staudinger reduction. Treatment of the Staudinger reaction iminophosphorane intermediate 26 with 1.05 equivalents of 2-t-(butoxycarbonyloximino)-2-phenylacetonitrile (Boc-on) led to Boc-protected amines 28 thru 32 in 87-100% overall yield.19 This process utilizes trimethylphosphine, which is more reactive than triphenylphosphine and provides an easier work-up because trimethylphosphine oxide is water soluble. It should be noted that the use of di-f-butyldicarbonate (B0C2O) has been investigated but leads to lower yields in comparison.20... 

Deprotection. For removal of the 2,2,2-trichloroethoxycarhonyl group from a protected amino acid, Cd in 1 1 HOAc-DMF is a reagent superior to Zn. A didehydro-indolizidine has been synthesized directly from a carbamate containing a diketo chain involved liberating the amine with sonication. 

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