Scheme 1. Synthesis of enantiomerically enriched g-lactams through auto-tandem asymmetric catalysis using 1.

Enantioselective allylic substitution catalyzed by transitionmetal complexes is an important process in organic synthesis.[1] For many years, mainly palladium complexes that contain chiral ligands have been employed as efficient catalysts in these reactions. Recent studies have demonstrated that chiral catalysts based on other transition metals show different regioselectivity in the synthesis of branched allylic products via monosubstituted p-allyl intermediates. [2] Although a variety of carbon and nitrogen nucleophiles can be used in those reactions, applicable oxygen nucleophiles are still limited to phenols and alcohols, which produce allylic ethers.[3] Thus, enantioenriched branched allylic alcohols, which serve as useful chiral building blocks, are often synthesized by other processes, such as the hydrogenation of a,b-unsaturated ketones, [4] the nucleophilic addition of vinylmetal reagents to aldehydes and ketones, [5] and the kinetic resolution of racemic allylic alcohols.[6] Recently, new ways to access these compounds have been developed, and they involve allylic substitution by a two-step conversion involving allylic esters and silyl ethers (Scheme 1; OPG = ester or silyl ether). [7,8] In the reaction of allylic chlorides with boronic acids in the presence of a ruthenium catalyst, the allylic alcohols were synthesized but high regio-and enantioselectivities were not achieved.[9] Herein, we describe the direct synthesis of chiral allylic alcohols by the regio-and enantioselective allylic substitution using water as the nucleophile.[10]Previously, we reported the enantioselective allylic substitution of 1,3-disubstituted allylic carbonates with amine and carbon nucleophiles catalyzed by planar-chiral cyclopentadienyl ruthenium (Cp'Ru) complexes (1; see Table 1). [11] This system was successfully extended to the regio-and enantioselective allylic substitution of monosubstituted allylic halides with oxygen and carbon nucleophiles. [12] From those studies, we found that Cp'Ru catalysts showed characteristic reactivity towards the less reactive nucleophiles. Thus, we started an examination of the enantioselective allylic substitution with water using Cp'Ru catalysts.Treatment of cinnamyl chloride (2 a) with water in the presence of 1 mol % of the Cp'Ru complex (S)-1 a resulted in the selective formation of the branched allylic alcohol (3 a; see equation in Table 1). After optimization of the reaction conditions, we found that the reaction in a mixture of THF/ water (8:1) at 25 8C with sodium hydrogen carbonate (1.2 equiv), produced 3 a after 4 hours in 99 % yield with 81 % ee.[13] Notably, the linear allylic alcohol was not formed at all. To improve the enantioselectivity, we examined the effect of the aryl groups on the phosphine ligand of the Cp'Ru catalyst (Table 1). Replacement of the phenyl groups with 3,5-dimethylphenyl and 4-methoxy-3,5-dimethylphenyl groups led to an increase in enantioselectivity to 88 % ee and 90 % ee, respectively (Table 1, entries 2 and 3). Complexes 1 d and 1 e, which have 3,...

Molecular design involving the incorporation of an α-amino acid residue into the side chain or main chain of a polymer is often used to stabilize artificial molecular architectures through intramolecular hydrogen bonding. However, this molecular design strategy rarely considers the importance of interactions between substituents at the α-position of amino acid moieties, as found in nature. Herein, we report the synthesis of a novel series of π-stacked helical poly­(quinolylene-2,3-methylene) with amino acid derivatives bearing different substituents at the α-position. We found that the thermal stability of π-stacked helical poly­(quinolylene-2,3-methylene) is significantly improved by packing the substituents in the empty spaces between the side chains. In particular, when a bulky cyclohexyl alanine derivative was used as the side chain, the π-stacked helical structure maintained its stability even in dimethylsulfoxide, a hydrogen bond competitor. The stabilization of the π-stacked structure by the amino acid substituents resulted in a unique polymerization behavior involving nucleation–elongation steps. In the case of derivatives with leucine and cyclohexyl alanine, which form stable π-stacked helical structures, metastable structures with entangled main chains were formed in the initial polymerization stage. These structures subsequently underwent an irreversible structural change to achieve a thermodynamically stable helical π-stacked conformation as a nucleus for subsequent polymerization. Thereafter, the polymerization reaction proceeded with the elongation of the π-stacked helical structure. Differences in the stability of these systems indicated that the amino acid substituents on the side chains determine the most thermodynamically stable π-stacked helical structure.

An asymmetric allylic substitution with sodium carboxylate using a planar-chiral cyclopentadienyl ruthenium complex has been developed. Optically active allylic esters were prepared in good yields with high regio- and enantioselectivities.

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