Yukihiko Hashimoto

Five-year study on the autumn food habits of the Asiatic black bear in relation to nut production

We studied the autumn food habits of the Asiatic black bear (Ursus thibetanus) from 1993 to 1997, based on 202 fecal samples in the Chichibu Mountains, central Japan. Nuts occupied the highest proportions of autumn foods (59.9–85.8% important values). Although the proportion of nuts of Quercus crispula, Fagus crenata and Fagus japonica varied greatly between the years, acorns of Q. crispula were most prevalent in four of the five years. We also determined the relative nut production of these three species by counting the number of nuts or cupules on the ground. Black bears consumed the nuts according to their relative availabilities. Nuts of Q. crispula appeared to be the most important food because: (i) these nuts were eaten in the highest proportion in four of the five study years; and (ii) even in poor years the bears consumed acorns of Q. crispula, whereas nuts of Fagus spp. were not consumed. We discuss the significance of alternative foods for black bears in relation to food tree diversity in the forest and the necessity for long-term studies examining the food habits of Asiatic black bears.

Phosphane Sulfide/Octacarbonyldicobalt‐Catalyzed Pauson – Khand Reaction Under an Atmospheric Pressure of Carbon Monoxide

Convenient access to cyclopentenones is provided by catalytic intra- and intermolecular Pauson - Khand reactions in the presence of octacarbonyldicobalt and tributylphosphane sulfide (see scheme). In contrast to other reactions of this type, they proceed under mild conditions (70 degrees C, 1 atm CO), and commercially available [Co(2)(CO)(8)] can be used without further purification.

Phosphine sulfides: Novel effective ligands for the palladium-catalyzed bisalkoxycarbonylation of olefins

Abstract Phosphine sulfides were found to be effective as a ligand in the palladium(II)-catalyzed bisalkoxycarbonylation of olefins. Aromatic olefins and vinylsilanes were converted into the corresponding succinates in high yields under mild conditions. Enantioselection was observed when chiral bisphosphine sulfides were used as ligands.

Design of resolving reagents: p-substituted mandelic acids as resolving reagents for 1-arylalkylamines

Abstract The resolution of 1-arylalkylamines 2–10 by mandelic acid 1 was studied. It was found that a substituent, which elongated the molecular length of the amines, diminished the resolution efficiency. On the basis of these results, (S)-p-methylmandelic acid (S)- 11 and (R)-p-methoxymandelic acid (R)- 12 were selected as new resolving reagents for the 1-arylalkylamines; these acids were found to have a higher resolving ability than (R)- 1 .

An efficient phosphorus-containing oxazoline ligand derived from cis-2-amino-3,3-dimethyl-1-indanol: application to the palladium-catalyzed asymmetric Heck reaction

Abstract Enantiopure 2-[2-(diphenylphosphino)phenyl]oxazoline, derived from a non-natural chiral aminoalcohol, cis -2-amino-3,3-dimethyl-1-indanol, was found to be an efficient ligand for the palladium-catalyzed asymmetric Heck reaction.

Diastereoselective ring-opening aldol-type reaction of 2,2-dialkoxycyclopropanecarboxylic esters with carbonyl compounds. 1. Synthesis of cis 3,4-substituted .gamma.-lactones

The Lewis acid-promoted reactions of 2,2-dialkoxycyclopropanecarboxylic esters 4a-c with aldehydes and unsymmetrical ketones to give γ-lactones were investigated. TiBr 4 is an excellent catalyst and gives cis 3,4-substituted γ-lactones in good yields with high diastereoselectivity. SnBr 4 promotes the reaction of 4a-c with aldehydes with high cis-selectivity, but does not promote the reaction of 4a with unsymmetrical ketones. ZrCl 4 is moderately trans-selective in the reaction of 4a with unsymmetrical ketones. Cis γ-lactones can be converted into their trans-isomers by treatment with NaOEt in EtOH

The highly syn-selective Michael reaction of enamines with 2-(1-alkenyl)-1,3-dioxolan-2-ylium cations generated from 2,2-dimethoxyethyl 2-alkenoates in situ

Abstract 2,2-Dimethoxyethyl 2-alkenoates are easily transformed into 2-(1-alkenyl)-1,3-dioxolan-2-ylium cations in situ on the action of titanium tetrachloride, which react with enamines to predominantly give syn Michael adducts in good yields. This is the first example of such a high syn -selectivity for the Michael reaction of α,β-unsaturated ester derivatives with ketone enolate equivalents.

Diastereoselective ring-opening aldol-type reaction of 2,2-dialkoxycyclopropanecarboxylic esters with carbonyl compounds. 2. Synthesis of cis-2,3-substituted-γ-lactones☆☆☆

Abstract The reaction of 3-alkyl-2,2-dialkoxycyclopropanecarboxylic esters 1d–i with symmetrical ketones and formaldehyde was investigated. Cyclopropanes 1d–i react with symmetrical ketones and formaldehyde in the presence of TiCl 4 to give cis -2,3-substituted-γ-lactones in good yields with high diastereoselectivity. In the reaction of 3-ethylcyclopropane 1d , the reaction conditions hardly influenced the diastereoselectivity. Regarding the reaction of 3-methylcyclopropane 1f , however, the effect of the reaction conditions, especially the solvent, on the diastereoselectivity was observed. High chemoselectivity was also observed for the reaction of 1d with 1,4-cyclohexanedione mono -ethylene acetal ( 24 ). The isomerization of cis -γ-lactones by treatment with NaOEt in EtOH gives trans -isomers in good yields.

Photoisomerization of ammonium α,β-unsaturated carboxylates in the solid state: effect of the hydrogen-bond network on the reactivity

EZ-Photoisomerization has been attained for several kinds of salts of α,β-unsaturated carboxylic acids with amines. This photoreaction has been proven to be an effective method for preparing (Z)-isomers from ammonium (E)-α,β-unsaturated carboxylates. The isomerizability is strikingly altered upon changing the ammonium group, which implies that the crystal structure affected the reactivity to a considerable extent. However, the cavity in the crystal has been found to have less influence than expected on the isomerizability. A further detailed study concerning the crystal structures suggested that the characteristics of the hydrogen-bond network had a close correlation with the isomerizability. Moreover, both the bulkiness of the carboxylate and ammonium groups as well as their difference in molecular length are considered to be the most important factors influencing the isomerizability.

Design, synthesis, and optical resolution of a novel non-natural chiral auxiliary, 1-(2,5-dimethoxyphenyl)ethylamine. Application to diastereoselective alkylation of aldimines

Abstract A chiral amine, 1-(2,5-dimethoxyphenyl)ethylamine, was found to be an effective chiral auxiliary for the diastereoselective alkylation of its aldimines with alkylmetals. The 1-(2,5-dimethoxyphenyl)ethyl group of the chiral auxiliary could be removed by the acetylation and then oxidation of the resultant alkylated product, accompanying an amino-transfer from the chiral auxiliary to the final product. Racemic 1-(2,5-dimethoxyphenyl)ethylamine could be easily synthesized from 1,4-dimethoxybenzene and resolved by the diastereomeric salt formation with mandelic acid to give both enantiomers in pure forms.