Allylic substitution reactions derivatives

The catalytic enantioselective desymmetrization of meso compounds is a powerful tool for the construction of enantiomerically enriched functionalized products." Meso cyclic allylic diol derivatives are challenging substrates for the asymmetric allylic substitution reaction owing to the potential competition of several reaction pathways. In particular, S 2 and 5n2 substitutions can occur, and both with either retention or inversion of the stereochemistry. In the... 

RhClCO(dppp) 2] for the sequential construction of an enyne precursor, starting from a malonic acid derivative and allylic acetate, which was converted in situ to the cycloaddition product with excellent yields. Obviously, the Pd complex catalyzes the allylic substitution reaction, while the rhodium catalyst is responsible for the PKR (Eq. 6). 

The moderate ees obtained with the copper arenethiolate ligands discussed above prompted a search for new chiral ligands for use in asymmetric allylic substitution reactions. The binaphthol-derived phosphoramidite ligand 32, used successfully by Feringa et al. in copper-catalyzed 1,4-addition reactions [37], was accordingly tested in the reaction between 21 and n-BuMgl. 

Complexes derived from the oxazolinylpyridine ligand Ph-Pybox and [Ir(COD)Cl]2 catalyze allylic substitution reactions of several oxygen and nitrogen nucleophiles... 

The configuration of the chiral BlNOLate backbone of the phosphoramidite ligand affects the rates and enantioselectivities of allylic substitution reactions. Hartwig and coworkers found that allylic substitution conducted with a catalyst derived from the simplified ligand (5a,/ )-L4 occurred more slowly than that conducted with a catalyst derived from (/ a,/ )-L4 [74]. Complexes of the mismatched (5a,/ )-L4 undergo cyclometalation slowly. The products formed from reactions catalyzed by complexes of (5a,/ )-L4 and (/ a,/ )-L4 have the opposite absolute configuration. 

Strategies centered on reductive introduction of the fluoroolefin via a geminal difluoro allylic array have been reviewed [66]. In an introductory example to this synthetic approach, Okada et al. [67] developed a completely stereoselective synthesis of Z)-2,5-syn 2-alkyl-4-fluoro-5-hydroxy-3-alkenoic acids through the Cu(l)-mediated allylic substitution reaction of trialkylaluminum with the (E)-4,4-difluoro-5-hydroxyallylic alcohol derivative (61) (Scheme 21). Reaction... 

K. S. Groninger, K. F. Jager, and B. Giese, Cyclization reactions with allyl-substituted glucose derivatives, Liebigs Ann. Chem. p. 731 (1987). 

Recently, Majoral et al. described the synthesis of a third-generation phosphorus-containing dendrimer possessing 24 chiral iminophosphine end groups derived from (2S)-2-amino-l-(diphenylphosphinyl)-3-methylbutane (Fig. 11) [32]. The dendritic catalyst was tested in allylic substitution reactions, using rac-(.E)-diphenyl-2-propenyl acetate or pivalate as substrates. The observed enantioselectivities were good to excellent (max. 95% ee) in all reactions. After completion of the catalytic reaction, the catalyst could be reused at least twice after precipitation and filtration. A slight decrease... 

Tridentate salen ligands (10) derived from 1 have given excellent results in the enantiocontrol of the hetero Diels-Alder addition reaction of dienes with aldehydes (eq 7) and in the asymmetric additions of TMS-azide to mc5o-epoxide and trimethylsilyl cyanide to benzaldehyde (up to 85% ee). Phosphino-oxazolines derived from 1 have been employed for the asymmetric control of palladium-catalyzed allylic substitution reactions products of 70-90% ee were obtained. Photolysis of crystalline adducts of enantiomerically pure 1 with prochiral alcohols results in asymmetric inductions of up to 79% in a rare example of a solid-state enantioselective reaction. ... 

Optically active ferrocenylbisphosphines, (/J)-N,iV-dimethyl-l-[(5)-1, 2-bis(diphenylphosphino)ferrocenyIJethylamine [(/J)-(5)-BPPFA] and its derivatives, are efficient chiral bisphos-phine ligands for rhodium-catalyzed asymmetric hydrogenation, palladium-catalyzed asymmetric allylic substitution reactions, and gold-catalyzed asymmetric aldol-type reactions of a-isocyano carboxylates. ... 

Substrates derived from meso-cycloalkenediols such as 41 are a highly versatile starting materials for enantioselective allylic substitutions [15]. Regioselective displacement of one of the enantiotopic leaving groups by the chiral catalyst leads to a chiral allyl intermediate 42 which is attacked regioselectively at the ster-ically less hindered position to afford product 43 (Scheme 17). Products of this type can be converted to variety of useful compounds by a second allylic substitution reaction. 

Activated methylene compounds such as dimethyl malonate have found substantial utility in palladium catalyzed allylic substitution reactions. Accordingly, the Krapcho decarboxylation is often used in conjunction with these reactions. As an example, the first total synthesis of enantiomerically pure (-)-wine lactone has utilized the sequence of reactions.27 First, the allylic substitution reaction of 2-cyclohexen-l-yl acetate (49) with alkali sodium dimethylmalonate yielded 51 with high enantioselectivity, as a result of the use of chiral phosphine ligand 50. The malonate was then subjected to Krapcho decarbomethoxylation using NaCl, H2O, and DMSO at 160 °C to yield 52. This reaction has been used similarly following the allylic substitution reaction with other malonate derivatives.28-30... 

Displacements involving allylic systems. Allylic substitution reactions continue to receive considerable attention. Improvement by microwave is noted. " New ligands for the Pd-catalyzed reaction include iminophosphine 13, which is derived from 1-mesitylethylamine, pyridylphenylphosphine 14, and the phosphinite 15, obtained from D-glucosamine. Phospholanes such as 16, 17, 18, prepared from mannitol, are excellent ligands. 

The range of carbon nucleophiles that can be used in the catalytic allylic substitution reaction is not unlimited. The use of more basic reagents, such as alkyllithiums or cuprates, usually results only in reduction of the allylic substrate. Malonate derivatives, enol stannanes, enamines, and stable enols, however, can give allylation products. 

---