Dehydration reactions in water have been realized by a surfactant-type catalyst, dodecylbenzenesulfonic acid (DBSA). These reactions include dehydrative esterification, etherification, thioetherification, and dithioacetalization. In these reactions, DBSA and substrates form emulsion droplets whose interior is hydrophobic enough to exclude water molecules generated during the reactions. Detailed studies on the esterification revealed that the yields of esters were affected by temperature, amounts of DBSA used, and the substrates. Esters were obtained in high yields for highly hydrophobic substrates. On the basis of the difference in hydrophobicity of the substrates, unique selective esterification and etherification in water were attained. Furthermore, chemospecific, three-component reactions under DBSA-catalyzed conditions were also found to proceed smoothly. This work not only may lead to environmentally benign systems but also will provide a new aspect of organic chemistry in water.

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A synthetic route to enantiomerically pure (1R,2S)-1-phenylphospholane-2-carboxylic acid (1), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation-carboxylation of the 1-phenylphospholane borane complex 3 by using sBuLi/1,2-dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine-coordinated alpha-phosphinoalkyllithium borane complex 4, was investigated by employing lithiodestannylation-carboxylation of both diastereomers of the 1-phenyl-2-trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at -100 degrees C. The key intermediate, the DPE-coordinated trans-1-phenyl-2-phospholanyllithium borane complex 9, was isolated, and the structure was identified by X-ray crystal structure analysis. This is the first X-ray crystal structure determined for an alpha-monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li--C bond (2.170 A) has been confirmed. Moreover, (1)H-(7)Li HOESY and (6)Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9, its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at -100 degrees C. Finally, 1 was used as a chiral ligand in a palladium-catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.

New types of P,N-ligands, cis-and trans-3, containing a tetrahydroisoquinoline skeleton as an N-donor were synthesized from (1R,2S)-1-phenylphospholane-2-carboxylic acid (phenyl-P-proline, 1). The cis isomer, cis-3, was found to act as an excellent ligand in palladium-catalyzed asymmetric allylic substitution reactions. The reactions of 1,3-diphenyl-2-propenyl acetate (5) with several nucleophiles in the presence of [Pd(p-allyl)Cl] 2 , cis-3 (Pd : ligand ¼ 1 : 2), and a base afforded the desired products in high yields with high enantioselectivity. It was suggested that these ligands did not serve as P,N-bidentate ligands but as P-monodentate ligands in these reactions.Keywords: allylic substitution; asymmetric catalysis; palladium; P,N-ligands The design and synthesis of chiral phosphine ligands have played a significant role in the development of transition metal-catalyzed asymmetric reactions.[1]Among them, P-stereogenic tertiary phosphines provide one of the most important and promising ligands. [2] On the other hand, chiral bidentate ligands with two different donor atoms (so-called hybrid ligands) also give effective asymmetric environments, and the catalytic ability of metal complexes with these ligands has been well documented.[3] One advantage of this type of chiral ligand lies in the difference in trans influence between two donor atoms.[4] Furthermore, coordination ability of the donor atoms may affect reactivity and stereoselectivity in asymmetric catalysis.[5] Recently, we have designed a new type of P-stereogenic phosphine, (1R,2S)-1-phenylphospholane-2-carboxylic acid (phenyl-P-proline, 1), and established an efficient synthetic route to it.[6] The P-stereogenic phosphine constructed an asymmetric environment near the palladium center, and consequently, exhibited good enantioselectivity in a palladium-catalyzed asymmetric allylic substitution reaction. To obtain higher enantioselectivity, a new class of P,N hybrid ligand 2 has been designed (Scheme 1). Herein, we report the synthesis of 2 and its use in palladium-catalyzed allylic substitution reactions.New types of hybrid P,N-ligands 3 containing a tetrahydroisoquinoline skeleton as an N-donor were synthesized from 1 via intermediate amides 4 as shown in Scheme 2. The synthesis of the intermediate 4 was achieved by amidation of 1 with 1,2,3,4-tetrahydroisoquinoline in the presence of 1-hydroxy-7-azabenzotriazole (HOAt), [7] and a mixture of isomers, trans-4 and cis-4, was obtained in high yield with a ratio of 52 : 48, respectively. These isomers could be easily separated by column chromatography on silica gel. When the reaction was conducted in the absence of HOAt at 0 8C, trans-4 was obtained selectively in good yield (trans-4:cis-4 ¼ 95 : 5). Borane reduction of the amide group of 4 followed by deboronation [8] of the phosphorus by treatment with pyrrolidine afforded trans-3 and cis-3 in good yields, respectively.The P,N hybrid ligands thus prepared were first evaluated in the palladium-catalyzed asymmetric allylic substitution of ...