A simple, efficient, and eco-friendly protocol for the N-Boc protection of the amine moiety in a variety of compounds with di-tert-butyl dicarbonate under water-acetone catalyst-free conditions is described. The corresponding monocarbamate is obtained in excellent yields on short reaction times. No competitive side reactions such as isocyanate urea and O-Boc were observed. This method represents a reasonable alternative to the previous reported protection procedures. 1. Introduction The protection of a functional group can be essential in the chemistry of poly functionalised molecules, when a reaction has to be carried out in a part of the compounds without the rest perturbing of the molecule. The development of simple and eco-friendly methods for the protection and deprotection of functional group continues to be a significant tool in synthetic chemistry of polyfunctional molecules [1, 2]. Nitrogen protection continues to attach a great deal of attention in a wide range of chemical fields, such as peptides, nucleosides, heterocyclic compounds, and other natural products. The protection of amines with tert-butyloxycarbonyl (Boc) group is a widely used reaction in organic synthesis because of its inertness toward catalytic hydrogenolysis and resistance toward hydrolysis under most basic conditions and nucleophilic reagents [3]. N-Boc deprotection is generally achieved under mild acidic conditions such as trifluroacetic acid (TFA), aqueous phosphoric acid in THF [4], or Lewis acid [5]. The deprotection can be carried out with montmorillonite K.10 clay [6], silica gel at low pressure [7], and by thermolytic cleavage although at high temperature [8, 9]. The tert-butyloxycarbonyl (Boc) is easily introduced using commercially available di-tert-butyldicarbonate (tert-BuOCO)2O under standard basic conditions. Various reagents and methods have been developed in the last years for the N-tert-butyloxycarbonylation of amines. Most are carried out in the presence of an organic or inorganic base. Amines are converted to N-tert-Boc derivatives by reaction with di-tert-butyldicarbonate (Boc)2O in the presence of: 4-(dimethylamino)-1-tert-butylcarbonylpyridinium DMAP [10], 4-(dimethylamino)-1-tert-butylcarbonyl pyridinium chloride [11] or tetrafluoroborate in aq NaOH [12], tert-butyl-2-pyridyl carbonate in the presence of K2CO3 in H2O-DMF [13] or tert-butyl 1-chloroethyl carbonate in presence of K2CO3 in H2O-THF [14], 2-tert-butyloxycarbonyloxyimino-2-phenylacetonitrile in the presence of Et3N in H2O-dioxane [15]. However, these protocols have various drawbacks as long
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