Allyl esters amine protecting group

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... 

Another method for deallylation of allyl esters is the transfer of the allyl group to reactive nucleophiles. Amines such as morpholine are used[415-417], Potassium salts of higher carboxylic acids are used as an accepter of the allyl group[418]. The method is applied to the protection and deprotection of the acid function in rather unstable /3-lactam 664[419,420]. 

Schreiber et al. have been able to apply their enediyne intramolecular Diels-Alder approach to the synthesis of dynemicin model systems [268-270], culminating in the total synthesis of di- and tri-O-methyl dynemicin A methyl esters 388 and 389 (Scheme 7-78) [271], derivatives of the natural product itself. Highlights of this synthetic approach include (a) intramolecular lactonization and concomitant Diels-Alder cyclization (380- 381) (b) allylic hydroxylation followed by an allylic diazene rearrangement in order to regiospecifically isomerize a double bond (381 - 382) (c) a-hydroxylation of the lactone 381 and subsequent conversion to the P-ketoester 383 (d) annelation of the anthraquinone unit (383- 384- 385- 386) (e) mild base-induced P-elimination of the N-protecting group of 386 to give the free amine 387 and (f) a final oxidation to complete the anthraquinone (387 - 388). 

By changing the surface characteristics of the solid support from neutral to acidic, the cleavage of the 9-fluorenylmethoxycarbonyl (Fmoc) group and related protected amines can be achieved in a similar manner. The hydrolytic deprotection of carboxylic acids from their corresponding allyl esters, under dry conditions , has also been reported on montmorillonite KIO clay [86]. 

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. 

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