Allylic groups, transfer palladium-catalyzed

Common protectors of hydroxyls are benzyl and 2-bromobenzyl for Boc chemistry and tert-butyl for Fmoc chemistry. Trityl provides a third level of selectivity for both chemistries because it can be removed by mild acid (1% CF3C02H in CH2C12), which does not affect tert-butyl based protectors. O-Allyl is not removable by palladium-catalyzed allyl transfer, so it is not appropriate. Protection by acyl such as benzyloxycarbonyl is possible, but 0 -acyl protectors can be problematic because of their tendency to shift to adjacent amino groups (see Section 6.6) and... 

In both schemes cis insertion is the most hypothetical step. Cossee has assumed 164) that similar processes take place during olefin polymerization in the presence of Ziegler-Natta catalysts, and in some other reactions catalyzed by the transition metal compounds. This author came to the conclusion 165) that the d orbitals of the metal combine with the migrating group to facilitate such processes. In the course of 7r-allyl transfer the palladium orbitals overlap with the antibonding orbitals of double bond of the <7-bonded allyl group so as to favor an insertion reaction. 

Scheme 11 Palladium-Catalyzed Transfer of an Allyl Group to a Nucleophilel ...

Atkins, K. E., Walker, W. E., Manyik, R. M. Palladium catalyzed transfer of allylic groups. Tetrahedron Lett. 1970, 3821-3824. 

The alkoxydi(sulfonyl)methane shown in Scheme 128 (entry b) has been used as a useful carbonyl 1,1-dipole synthon ( C°-0). Its alkylation with alkyl halides is best achieved using CS2CO3 in DMF at 50 °C, and its palladium-catalyzed allylation requires the use of phase-transfer conditions (Scheme 128, entry b). The unmasking of the carbonyl group was then achieved by reacting the resulting disulfone with boron trichloride (-78 C, CH2CI2) followed by the addition of alcohols or amines to provide esters or amides respectively (Scheme 128, entry b). ... 

Palladium acetoacetonateltriphenylphosphine Palladium-catalyzed transfer of allylic groups... 

Homoallylic alcohol 9 is readily prepared by palladium-catalyzed directed cyanoboration followed by Suzuki-Miyaura cross-coupling (Scheme 5.15) [15]. Palladium-catalyzed allyl transfer from 9 to aryl bromide results in removal of the hydroxymethyl directing group and concomitant formation of 3,4-diaryl-2-butenenitrile albeit the lack of regio- and stereospecificity. The overall transformation proposes a concept of intramolecular reaction with a carbon tether removable through retro-allylation. 

Organozirconocene Chlorides. Acyl zirconocene chlorides function as efficient donors of acyl anions and can react with allylic or propargylic halides (X=Cl, Br, I, OTs) under Cul catalysis. In these reactions, acyl copper species (RCOCu), generated by the transfer of acyl group fromZr to Cu, were speculated to be the reactive species. These Cul-catalyzed reactions of acyl zirconocene chloride are cort5)lementary to the palladium-catalyzed reactions and enable the formation of -y-unsaturated ketones, which suffer ready isomerization under the palladium-catalyzed conditions (eq 23). On the other hand, carbonylative cross-coupling of F-o -selanylvinylzirconiums with alkynyUodonium tosylates can be performed in THF in the presence of 3 mol% of Cul and atmospheric pressure of carbon monoxide in a palladium-free system. 

The allylic HYCRAM derivative was subsequently modified by insertion of a standard amino acid between the aminomethyl resin and the hydroxy butenoic acid moiety. Using this allylic anchor, the resin-linked, glycosylated HIV peptide T-derivative 164 was synthesized by application of Fmoc amino protection and sidechain protection with lert-butyl groups. The lac-tosamine peptide T (165) could be released from the resin by application of the palladium(0)-catalyzed allyl-transfer reaction to V-methyl aniline as the allyl acceptor. 

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