Protecting groups allyl esters

Carboxylic acids are protected as allyl esters. In the final step of the total synthesis of reveromycin B, three allyl ester groups in 466 were removed cleanly with HC02H/Et3N to give reveromycin B in 62% yield [174],... 

Moving away from ketones to other prochiral nucleophiles has also been an important goal in our group. We choose to explore lactam-derived substrates in part because we envisioned that the products formed would be useful intermediates in the synthesis of various alkaloids and because we would be able to modulate the electronics and sterics of the lactam enolate by attaching different groups at nitrogen with the aim of optimizing the enantioselectivity of the allylic alkylation. In the event, we chose to initially test tosyl-protected lactam allyl ester 29 and Boc-protected lactam aUyl ester 30 with two Pd PHOX catalysts in several solvents (Scheme 18). 

The Noc group, developed for amino acid protection, is introduced with the acid chloride (Et3N, H2O, dioxane, 2 h, 20°, 61-95% yield). It is cleaved with Pd(Ph3P)4 (THF, A, A -dimethyibarbituric acid, 8 h, 20°, 80% yield). It is not isomerized by Wilkinson s catalyst, thus allowing selective removal of the allyl ester 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... 

Synthesis of Characteristic Lipopeptides of Lipid Mode-fied Proteins Employing the Allyl Ester as Protecting Group, T. Schmittberger, A. Cotte, H. Waldmann, Chem Commun 1998, 937-940. 

H Kunz, H Waldmann, C Unverzagt. Allyl ester as temporary protecting group for the (S-carboxy function of aspartic acid. Int J Pept Prot Res 26, 493, 1985. 

Peptide 21, synthesized using the C-terminal enzymatic-cleavable choline ester (Scheme 11), was also synthesized using the C-terminal allyl ester protecting group (Scheme 12). The selective Pd(0)-catalyzed... 

Scheme 15 Synthesis of the doubly palmitoylated heptapeptide corresponding to the C-terminus of hemagglutinin A bearing an N-terminal NBD function using Boc, Aloe, and the allyl ester as protecting groups.

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