Allyloxycarbonyl group

PdCl2(Ph3P)2, dimedone, THF, 95% yield. This method is also effective for removing the allyloxycarbonyl group from alcohols and amines. 

O Dangles, F Guibe, G Balavoine, S Lavielle. A Marquet. Selective cleavage of the allyl and allyloxycarbonyl groups through palladium-catalyzed hydrostannolysis with tributyltin hydride. Application of the selective protection-deprotection of amino acid derivatives and in peptide synthesis. J Org Chem 52, 4984, 1987. 

F.Guibf and Y. Saint M Leux, The allyloxycarbonyl group for alcohol protection Quantitative removal or transformation into allyl protecting group via w-allyl complexes of palladium, Tetrahedron Lett. 22 3391 (1981). 

In the last step of this sequence, the liberated functional group is again protected, but this time with the acid-stable allyloxycarbonyl group (alloc CH2=CHCH20C0R). 

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. 

A fourth urethane protecting group, the TV-allyloxycarbonyl group (Alloc) is introduced in the usual way using allyl chloroformate or diallyl dicarbonate. Its main interest concerns its removal by a Pd-catalysed hydrostannolysis with tri-butyltin hydride (Scheme 7.4). It thus provides orthogonal protection without the need to expose the peptide to acid, conditions that would cleave, for example, O-gly-coside derivatives of peptides. 

The preparation of the trisaccharide 11.40 was carried out by condensation of imidate 11.45 with acceptor 11.43 in the presence of TMSOTf to afford disaccharide 11.50 in 87% yield (Scheme 14). Conversion of 11.50 into glycosyl acceptor 11.51 was achieved by de-isopropylidination and acetylation followed by removal of the allyloxycarbonyl group. Glycosyl acceptor 11.51 was subsequently condensed with imidate 11.44 in the presence of BF3-Et20 to give the ttisaccharide derivative 11.52 in 81 % yield. The deprotection, oxidation, and N-acetylation sequence was achieved as described for 11.39 to afford 11.40 in 66% yield over fom steps. 

The preparation of tetrasaccharide 11.41 is outlined in Scheme 15. Boron tri-fluoride etherate mediated glycosylation of 11.51 with imidate 11.46 produced the corresponding trisaccharide (88%), which was readily converted to the glycosyl acceptor 11.53 upon removal of the allyloxycarbonyl group. Under TMSOTf-catalyzed... 

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