Esters allyloxycarbonyl

A Noble Metal-Sensitive Alternative Allyl Ester (All) and the Allyloxycarbonyl (Aloe) Croup... 

The selectivity and mildness of the Pd(0)-catalyzed deprotection of allyl (All) esters and the allyloxycarbonyl (Aloe) urethanes117 181 reaction also allowed for the successful and efficient application of this blocking group technology in the synthesis of acid- and base-labile lipidated pepti-... 

The combination of the N-terminal allyloxycarbonyl (Aloe) group (34) with the tert-butyl ester proved to be a particularly efficient tool in the synthesis of complex glycopeptides, as has been demonstrated in the synthesis of sensitive fucosyl chitobiose glycopeptides (19). The Aloe group was... 

N-Allyloxycarbonyl-aspartic acid a-tert-Butyl Ester 34... 

N2-(Allyloxycarbonyl)-N4-(2-acetamido-4-0-(2-acetamido-3,4-di-O-acetyl-6-O-benzyl-2-deoxy-fl-D-glucopyranosyl)-3-0-acetyl-6-0-(2,3,4-tri-0-benzyl-a-L-fucopyranosyl)-2-deoxy-pt-D-glucopyranosyl)-L-asparagine tert-Butyl Ester 35 [26]... 

The allyloxycarbonyl group [269] has shown a wide application in organic synthesis, especially in the fields of peptides, nucleotides, and carbohydrates. Allyloxycarbonyl derivatives are more easily prepared than the corresponding allyl ethers and they are more stable than ester protecting groups which find frequent use in carbohydrate chemistry. 

As has already been detailed for the allyloxycarbonyl (Aloe) moiety, allyl esters also proved to be very versatile and useful carboxy-protecting groups. They can be easily constructed by azeotropic esterification or nucleophilic displacement on allylic halides. For the cleavage of these esters lithium di-methylcuprate can be used. However, a much milder method is found in the Rh -catalyzed isomerization of the allyl moiety to a propenyl ester which immediately hydrolyzes under the reaction conditions (Scheme 67). Even milder is the Pd°-catalyzed allyl transfer to morpholine as an accepting nucleophile. The removal of allyl ester protection has earlier been used in particular in -lactam anti-... 

Deallylation. The utility of (V-allyloxycarbonyl derivatives in peptide synthesis is demonstrated by deprotection with the Pd-catalyst system in aqueous MeCN. Prenyl esters are not affected during deallylation. 

As an example, a new palladium based method has been developed for the alkylation of tyrosine residues [34], In this reaction, allylic carbonates, esters, and carbamates are activated by palladium(O) complexes in aqueous solution, resulting in the formation of electrophilic zr -allyl complexes (such as 16), Fig. 10.3-8(a). These species react at pH 8-10 with the phenolate anions of tyrosine residues, resulting in the formation of aryl ether 17 and regeneration of the Pd(0) catalyst. The reaction requires no organic cosolvent, is catalytic in palladium, and requires P(m-QjH4S03 )3 as a water-soluble phosphine ligand. In contrast to alkyl or allylic halides, the inert character of the allyloxycarbonyl compounds used in this reaction ensures that nonspecific... 

Peptide synthesis.- An Ai-allyloxycarbonyl derivative of an a-amino acid is deblocked by a combination of PhSiH and a Pd catalyst. When an activated ester of another amino acid is present, it will be attacked by the released amine. 

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