F-Butyl carbamates

Only a limited amount of water is added at this point because f-butyl carbamate has some solubility in the resulting aqueous slurry. With water-insoluble carbamates the amount of water added is immaterial. 

Hi. Intermolecular reactions of carbamates. Carbamates possess a more electron-rich nitrogen atom than amides or sulfonamides, and thus participate more readily in palladium-catalyzed aminations of aryl halides. For example, f-butyl carbamate has been shown to react with aryl halides to form f-Boc protected anilines (equation 34)68. The catalyst... 

The related o-bromobenzyl carbonates have been developed for use in solid-phase peptide synthesis. An aryl o-bromobenzyl carbonate is stable to acidic cleavage (CF3CO2H) of a f-butyl carbamate a benzyl carbonate is cleaved. The o-bromo derivative is quantitatively cleaved with hydrogen fluoride (0°C, 10 min). ... 

Mg(C104)2, CH3CN, 99% yield. These conditions do not cleave a f-butyl ester or f-butyl carbamate. 

Hydrogenolysis. PMHS is a useful hydrogen source in the Pd-C-catalyzed hydrogenolysis of aziridines and organic azides. The amine products can be converted to f-butyl carbamates in situ by (Boc)20. 

Substitution of sulfenyl derivatives. An a-alkylthio A-Boc a-amino acid is easily synthesized from a thiol, f-butyl carbamate, and glyoxylic acid. Replacement of the alkylthio group by fluorenylmethylcarbamoyl unit gives a useful derivative for solid-phase synthesis of a-aminoglycine-containing peptides. The replacement is conveniently mediated by NBS. "... 

Cleavage of Carbamates. Since strongly acidic conditions are typically required for the deprotection of carbamates, use of TMS-I provides a very mild alternative. Benzyl and f-butyl carbamates are readily cleaved at rt, whereas complete cleavage of methyl or ethyl carbamates may require higher temperatures (reflux). The intermediate silyl carbamate is decomposed by the addition of methanol or water (eq 8). Since amides are stable to TMS-I-promoted hydrolysis, this procedure can be used to deprotect carbamates of amino acids and peptides. 

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