Allyl protection

The protected nucleoside-3-phosphoramidite monomer units such as 671 are used in the solid-phase oligonucleotide synthesis. In the 60mer synthesis, 104 allylic protective groups are removed in almost 100% overall yield by the single Pd-catalyze reaction with formic acid and BuNH2[432], N,(9-protection of uridine derivatives was carried out under pha.se-transfer conditions[433]. 

Protection for the double bond in the allyl protecting group may be achieved by epoxidation. Regeneration of the allyl group occurs upon... 

The use of various allyl protective groups in complex molecule synthesis has been reviewed. ... 

Allylic protection groups and their removal through catalytic palladium rr-allyl methodology in transformations of heterocycles 98T2967. [3- -3]Benzannelation of heteroaromatics consisting of successive nucleophilic... 

Allylic protection groups and their removal through catalytic palladium Tr-allyl methodology in synthesis of heterocycles 98T2967. 

A novel approach to 3-substituted indolines and indoles via the anionic cyclization of 2-bromo-lV,lV-diallyanilines has been developed simultaneously by Bailey <96JOC2596> and Liebeskind <96JOC2594>. Thus, treatment of 2-bromo-lV,lV-diallylanilines 78 with 2 equivalents of BuLi at -78 °C leads to the formation of the intermediate 79 which may be trapped with an electrophile to afford 3-substituted indolines 80. Aside from ease of preparation, an additional benefit of the intramolecular carbolithiation of <7-lithio-W,Al-diallyl-anilines is the production of Al-allyl-protected indolines, which are easily deprotected using... 

The rhodium-catalyzed isomerization of allylamine can be used for the deprotection of A-allyl protective groups (Scheme 7).19 20... 

The allyl protecting group has also been demonstrated to be useful for blocking of side-chain functionalities (36). Thus, the palladium(0)-catalyzed... 

AM Kimbonguila, S Boucida, F Guibe, A Loffet. On the allyl protection of the imidazole ring of histidine. Tetrahedron 53, 12525, 1997. 

Example 20 diallyl-iV,N-diisopropylphosphoroamidite has been prepared by Bannwarth and Kiing and employed in the phosphitylation of the peptide hydroxy function [49]. The phosphitylation by this reagent proceeds in the presence of tetrazole (step a) followed by CBPA oxidation (step b) and removal of allyl protecting groups in the presence of Pd(0)P(C6H6)3 (step c). 

Figure 6.12 Polystyrene-bound Schiff base (thio)urea catalysts HTS-optimized in the asymmetric Strecker reaction between N-allyl-protected benzaldimine and TBSCN key results obtained from the different libraries.

Scheme 6.40 Product range of the 11-catalyzed asymmetric Strecker reaction of aromatic and aliphatic N-allyl-protected aldimines.

In a preparation213 of 2,3,4-tri-O-benzyl-D-galactopyranose, allyl protecting-groups were removed from 0-1 and 0-6 of allyl 6-O-allyl-2,3,4-tri-0-benzyl- -D-galactopyranoside, and the allyl group has been used214 for the temporary protection of 0-2, 0-3, 0-4, or 0-6 in benzyl... 

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). 

The construction of the maleic anhydride moiety 44 in only five steps starts with the conversion of the amide into an appropriate thioester. Upon treatment with DBU, an aldol-type cyclization occurs to provide the /1-hydroxy thiolactone as a single diastereomer. After removal of the allylic protecting group, dehydration and decarboxylation are carried out simultaneously by simple heating. The thiobutenolide is oxidized to the corresponding thio-... 

Both routes actually use vanilly alcohol 34 (3-methoxy-4-hydroxybenzyl alcohol) as the starting material. Application of method (a) requires that 34 could be trimerized to C3-cyclotriguaiacylene, 5 (Table 1). However, as was said above, this reaction does not work, presumably because the phenolic group makes the molecule too reactive under the strong acidic conditions employed the allyl protected derivative 35 was thus used instead of 34 itself, and, on reaction with perchloric acid in methanol, gave the tris-allyl protected derivative 9 in 55% yield. Palladium catalysed cleavage of the allyl groups then led to the desired racemic triphenol 5. The latter could eventually be resolved by separation of its dia-stereoisomeric esters with co-camphanic acid [13]. 

Allyl protection of terminal a-carboxy groups has been used in convergent syntheses of N-linked glycopeptides on a solid support.PI For instance, the polymer-bound trisaccharide pentapeptide allyl ester 12 (Scheme 7) is built up by condensation of the polymer-linked trisaccharide with Z-Ala-Ile-Asp-Ile-Ser(Bzl)-OAl. Further conversion into the polymer-bound trisaccharide octapeptide derivative 14 is achieved by cleavage of the allyl ester with tetrakis(triphenylphosphine)palladium and A,A-dimethylbarbituric acid to give 13, followed by condensation with H-Asp(OMob)-Leu-Thr(Bzl)-OAl. The presence of the allyl ester group at the C-terminus of the octapeptide provides the opportunity for further chain elongation. 

Other ways to obtain 3-OH acceptors are the use of mannose precursors with a temporary 3-0-allyl protecting group in the Grignard reaction [16,18,20], or phase transfer benzylation [42] of a heptopyranosyl 2,3-diol, or benzylation of a tin-activated [43] heptofuranosyl 2,3-diol, both last methods giving preferentially the 2-0-benzyl derivative [27,15]. However, if the tin-assisted alkylation is performed on a heptopyranosyl 2,3-diol, the 3-0-alkyl derivative is the main product [5,28]. 

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