Protecting groups, allyl-based deprotections amines

Allyl carbonate esters are also useful hydroxy-protecting groups and are introduced using allyl chloroformate. A number of Pd-based catalysts for allylic deprotection have been developed.209 They are based on a catalytic cycle in which Pd° reacts by oxidative addition and activates the allylic bond to nucleophilic substitution. Various nucleophiles are effective, including dimedone,210 pentane-2,4-dione,211 and amines.212... 

Propargyloxycarbonyl (Poc) protected amines react with 1 at room temperature and the corresponding amines are obtained in quantitative yields. Deprotection of Poc in N-Poc-S-benzylcysteine ferf-butyl ester by 1 has resulted in a selective deprotection of Poc in the presence of methyl, allyl, and ferf-butyl esters (eq 20). Reaction of 1 with A(-Poc-S-benzylcysteine ferf-butyl ester is very facile under sonochemical conditions and provides the dipeptide [H2N-(Bzl)Cys-Cys(Bzl)-Ofiu] in 1 h at room temperature. Other protecting groups such as 5-benzyl and ferf-butyl groups are unaffected under these reaction conditions. Poc group is stable to acids and bases and deprotection of ferf-butyl and methyl esters is acconplished conveniently in the presence of W Poc protected amino acid derivatives. 

Initially, Pd-catalyzed deprotections were carried out under reductive conditions. The earliest examples of Pd-mediated allyl group deprotection employed formic acid, usually in conjunction with an amine base, at elevated temperature as a hydride source (Scheme 2). Later development of tri- -butyltin hydride as a hydride source has greatly facilitated the reductive deprotection of a wide variety of aUyl-based protecting groups, reacting almost instantaneously at ambient temperature. " Additional hydride sources for allyl group deprotection include phenyltrihydrosilane and several different borohydrides (Scheme Most recently, Guibe and Albericio have used amine-... 

A new protecting group for amines has been studied and used in the first chiral synthesis of anticapsin. The route involves initial bis-allylation to give a base-stable group resistant to nucleophiles, but which can be easily deprotected using the known allyl-to-propenyl isomerization reaction promoted by transition-metal complexes (Scheme 11). 

Based on facile formation of 7i-allylpalladium intermediates from various allylic compounds, allyl groups can be used for the protection of carboxylic acids, amines and alcohols. Deprotection can be achieved by two methods using Pd(0) catalysts [128,138]. In one method, the allyl group can be removed as propylene by Pd-... 

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