Abstract
The DTBB-catalysed lithiation of Boc-protected alcohols, amines and thiols in THF at 0oC led, after quenching with methanol or water, to the recovery of the free alcohols, amines and thiols in short reaction times and in moderate to very good yields. The procedure has been applied to primary, secondary and tertiary alcohols, phenols, secondary amines and primary, secondary and aromatic thiols. This method represents a reasonable alternative to the previously reported deprotection procedures.
Highlights
The protection of a functional group can be essential in the chemistry of polyfunctionalised molecules when a reaction has to be carried out in a part of the compound without perturbing the rest of the molecule
Reasons for the mentioned success of the butoxycarbonyl protecting group (Boc) group are the classical properties for a protecting group: (a) It is introduced using commercially available di-tert-butyl dicarbonate [ called tert-butyl pyrocarbonate: (ButOCO)2O] under standard basic conditions; (b) It is stable towards bases, as well as to catalytic hydrogenation and reduction with sodium in liquid ammonia; and (c) Its removal can be achieved under
The generally accepted mechanism for the cleavage of the Boc group under acidic conditions involves the formation of carbon dioxide and the tert-butyl cation, which after loosing a proton gives isobutene, so only volatile products are generated together with the desired deprotected product making the work-up of the reaction very convenient
Summary
The protection of a functional group can be essential in the chemistry of polyfunctionalised molecules when a reaction has to be carried out in a part of the compound without perturbing the rest of the molecule. Starting materials 1 were prepared from commercially available alcohols 2a-d, phenol 2e, amines 2f-h and thiols 2i-k by reaction with di-tert-butyl dicarbonate and a catalytic amount of 4-(dimethylamino)pyridine (DMAP; 1:0.4 molar ratio) in toluene at room temperature.
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