Tert-Butyloxycarbonyl protecting group

The tert-butyloxycarbonyl protecting group or tert-butoxycarbonyl protecting group (BOC group) is an acid-labile protecting group used in organic synthesis.

The BOC group can be added to amines under aqueous conditions using di-tert-butyl dicarbonate in the presence of a base such as sodium hydroxide:

Protection of amines can also be accomplished in acetonitrile solution using 4-dimethylaminopyridine (DMAP) as the base.

Removal of the BOC group in amino acids can be accomplished with strong acids such as trifluoroacetic acid in dichloromethane, or with HCl in methanol. A complication may be the tendency of the t-butyl cation intermediate to alkylate other nucleophiles; scavengers such as anisole or thioanisole may be used. Selective cleavage of the N-Boc group in the presence of other protecting groups is possible when using AlCl3.

Sequential treatment with trimethylsilyl iodide then methanol can also be used for Boc deprotection, especially where other deprotection methods are too harsh for the substrate. The mechanism involves silylation of the carbonyl oxygen and elimination of tert-butyl iodide (1), methanolysis of the silyl ester to the carbamic acid (2) and finally decarboxylation to the amine (3).

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