Regioselectivity allylic derivatives

A study of the regioselective lithiation of 1-substituted 1,2,4-triazoles has established that for 1-n-alkyl and 1-allyl derivatives monolithiation occurs at ring C(5) whereas 1-propargyl-l//-1,2,4-triazole initially undergoes lithiation at the y-position. ... 

Sodium hydroxide-induced partial allylation was used for preferential reaction at the equatorial OH-4 in l,6-anhydro-2-0-benzyl-P-D-galactopyranose [229]. A similar reaction of allyl 2,6-di-O-benzyl-a-D-galactopyranoside with allyl bromide and sodium hydroxide in benzene at room temperature was not as regioselective, the per-substituted 3,4-di-O-allyl derivative dominated in the reaction product [73]. A high, 87 % yield of the monoallyl derivative was obtained from 1,2 5,6-di-O-isopropylidene-D-mannitol after the treatment with allyl bromide and sodium hydroxide in aqueous acetone [230],... 

One important study on the regio- and stereoselectivity of the Pd(0)-catalyzed allylations of adenine 238 and the related 6-substituted 2-aminopurine derivatives 241 and 242 (Scheme 49) is that of Benneche and Undheim (92ACS761, 92TL1085). This group reported that adenine 238 is regioselectively allylated at N-9 both by allyl acetate and by rac-160 to afford 239 and rac-240 as the only isolated reaction products. However, when treated with allyl acetate, 241 and 242 afforded mixtures of N-allylation products at N-9 (243 and 244) and at N-7 (245 and 246). The ratios 243/245 and 244/246 indicate that the difference in reactivity between both positions is low. When both 241 and 242 were allylated with the more sterically demanding acetate rac-160, the ratio of N-9/N-7 allylation... 

Copper salts such as CuCN, CuBr-SMc2 and CuCN-2LiCl were demonstrated to mediate the regioselective allylation, alkylation, and propargylation of the lithium anion of n-butylthiooxazole 128 providing 2,5-disubstituted systems 129. Desulfurization with deactivated W2-Raney nikel produced 5-substituted derivatives <03TL7395>. 

Kresze et al. found that the ene product 117, after diazomethane treatment, formed a mixture of the 0- and N-methylated compounds 118 and 119, respectively [83] (Scheme 32). Only a year later Delerit et al. used this possibihty to 0-silylate S-allylsulfinamides derived from ene reactions between olefins and N-sulfinyl sulfonamides to develop a regioselective allylic amination sequence (Scheme 33) [84]. After the ene reaction had occurred the resulting sulfi-... 

We call this disconnection enolate allylation because we want to alkylate an enolate ion with an allyl halide. We have already discussed (chapter 19) the regioselectivity problems inherent in reactions of allyl derivatives and you should recall that we want to react at the correct (less substituted) end of the allyl system and we want to make an f-alkcnc. The solution is to use a [3,3]-sigmatropic rearrangement. This is the reaction sequence ... 

Allyl derivatives 11 with identical substituents at Cl and C3 are an important class of substrates for enantioselective allylic substitution (Scheme 10). Starting from either enantiomer (11 or ent-ll) the same allyl-palladium complex 12 is formed. Therefore, the first part of the catalytic cycle leading to this intermediate usually is irrelevant for the stereoselectivity of the overall reaction [31]. The two termini of the free allyl system are enantiotopic. If the catalyst is chiral, they become diasterotopic in the allyl-metal complex and, therefore, may exhibit different reactivities toward nucleophiles. Under the influence of a suitable chiral ligand attached to palladium, nucleophilic attack can be rendered regioselective leading preferentially either to product 13 or its enantiomer ent-l3. 

With acidic potassium dichromate adsorbed on silica-zirconia, regioselective allylic oxidation is achieved. This reagent is better than CrO -S.S-dimethylpyrazole for oxidation of 1-menthene derivatives because the 3-keto products are largely absent. 

A highly enantioselective and regioselective allylic substitution of the BH carbonates using nitroalkanes as nucleophiles was developed by Lu and co-workers [135] in the presence of quinidine-derived thiourea catalyst 76. The nitroalkanes was added to the BH carbonates in the 3 position (as depicted in Scheme 9.36) in good yields and enantioselectivities (Scheme 9.38). 

Allyl esters are known to react with palladium catalysts to afford 17 -allylpalladium complexes that can undergo a nucIeophiUc attack to give allylation products) " Accordingly, treatment of allyl carbonates with o-alkynyltrifluoroacetanilides or o-ethynyl-trifluoroacetanilide in the presence of Pd2(dba)3, dppb [l,4-bis(diphenylphosphino)butane] in THF at 60 °C affords the corresponding A-allyl derivatives in high yield, with the nitrogen-carbon bond formed regioselectively at the less substituted terminus of the allylic system. 

The direct ruthenium catalysed allylation with allylic alcohol derivatives of various aromatic compounds and heterocycles such as furans and thiophenes was performed by Nishibayashi with cationic thiolate-bridged diruthenium(III, II) catalysts. The reaction is consistent with an electrophilic aromatic substitution by the electrophilically activated allyl moiety [68]. Allylation also takes place with the alkene metathesis Grubbs catalyst [69]. More importantly using (phosphine-sulfonate)ruthenium(II) catalyst Bmneau et al. have recently shown that allyl alcohols are activated generating an allyl-ruthenium(IV) intermediate leading to C3-allylation of indole with high regioselectivity in favour of the branched allyl derivative [(Eq. 84)] [167]. 

Allylic acetoxy groups can be substituted by amines in the presence of Pd(0) catalysts. At substituted cyclohexene derivatives the diastereoselectivity depends largely on the structure of the palladium catalyst. Polymer-bound palladium often leads to amination at the same face as the aoetoxy leaving group with regioselective attack at the sterically less hindered site of the intermediate ri -allyl complex (B.M. Trost, 1978). 

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