Masayuki Hoshi

Dialkylborane-Catalyzed Hydroboration of Alkynes with 1,3,2-Benzodioxaborole in Tetrahydrofuran

Abstract Dialkylborane catalyzed hydroboration of alkynes with an equimolar amount of 1,3,2-benzodioxaborole in tetrahydrofuran efficiently to provide 2-alkenyl-1,3,2-benzodioxaborole under mild reaction conditions.

Dicyclohexylborane-Catalyzed Hydroboration of 1-Halo-1-alkynes with 9-Borabicyclo[3.3.1]nonane

Abstract A catalytic amount of dicyclohexylborane accelerates the hydroboration of 1-halo-1-alkyne (1) with 9-BBN to provide B-[(Z)-1-halo-1-alkenyl]-9-BBN (2) regio- and stereo-selectively.

Synthesis of hydroxycinnamoyl β-d-xylopyranosides and evaluation of their antioxidant properties

Various hydroxycinnamoyl β-d-xylopyranosides were efficiently prepared from 2,3,4-tri-O-acetyl-α-d-xylopyranosyl bromide (TAXB) with amine by amine-promoted glycosylation. The resulted acetylated hydroxycinnamoyl β-d-xylopyranosides with acetoxy groups at C-2, C-3, and C-4 were regioselectively deacetylated at C-4 position with Novozym 435. Antioxidant activities of free hydroxycinnamic acids and the respective β-d-xylopyranosides were evaluated by DPPH radical scavenging activity as well as their inhibitory effect on autoxidation of bulk methyl linoleate. The radical scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) decreased in the order ferulic acid>caffeic acid≈caffeoyl β-d-xylopyranosides≈sinapinic acid>sinapoyl β-d-xylopyranosides≈feruloyl β-d-xylopyranosides>p-coumaric acid>p-coumaroyl β-d-xylopyranosides. In bulk methyl linoleate, the antioxidant activity order against autoxidation was almost consistent with the scavenging activity order. The results showed that caffeoyl β-d-xylopyranosides and sinapoyl β-d-xylopyranosides were as effective as free caffeic acid, sinapinic acid, and ferulic acid.

Stereoselective Synthesis of (E)- and (Z)-1-Alkenyltributylstannanes From (E)- and (Z)-1-Alkenyldialkylboranes Using a Cross-Coupling Reaction with Tributyltin Halide

Abstract The cross-coupling reaction of ( E )- or ( Z )-1-alkenyldialkylborane with tributyltin halide using copper (II) acetylacetonate [Cu(acac) 2 ] as catalyst in the presence of NaOH proceeds under extremely mild and aqueous conditions to give ( E )- or ( Z )-1-alkenyltributylstannane stereoselectively.

Electrooxidative Conversion of Dibenzoylbenzene Dihydrazones into the Corresponding Bis-diazo Compounds and Bis-dimethyl Acetals

Several dibenzoylbenzene dihydrazones were electrochemically oxidized into the corresponding bis-dimethyl acetals in a methanolic solution containing sodium methoxide and catalytic amount of KI. During electrolysis, the anolyte exhibited a characteristic deep purple, which strongly suggested that formation of a diazo compound as an intermediate. Interestingly, some of the diazo compounds could be isolated directly from the anolyte.

Reaction of [(Z)-1-bromo-1-alkenyl]dialkylboranes with N-halogeno compound in THF–DMF: a novel synthesis of 1,2-disubstituted (E)-vinyl bromides

Abstract DMF-induced reaction of [(Z)-1-bromo-1-alkenyl]dialkylboranes with an N-halogeno compound results in 1,2-migration of an alkyl group from the dialkylboryl group to the α-carbon atom without elimination of the bromine atom, followed by β-elimination to provide 1,2-disubstituted (E)-vinyl bromides stereoselectively in good yields.

A new facile route to primary alkanenitriles from terminal alkenes via a hydroboration–cyanation sequence

Terminal alkenes are converted into one-carbon homologated primary alkanenitriles in high yields via hydroboration followed by a reaction with copper(I) cyanide, copper(II) acetate, and copper(II) acetylacetonate.

Preparation of Optically Pure δ-Lactones Using Diastereomeric Resolution with Amino Acid as Resolving Agent

Synthesis of optically pure δ-lactones by diastereomeric resolution was investigated. Amino acid derivatives, which can be obtained at a relatively low cost, were used as resolving agents. Six optically pure δ-lactones were efficiently synthesized using Cbz-L-alanine without other expensive resolving agents. Both enantiomers of δ-lactone obtained had over 98% enantiomeric excesses. This diastereomeric resolution is very efficient for the preparation of optically pure δ-lactones.

Electrooxidative Cyclization of Hydroquinolyl Alcohols, Hydroquinolylamines, and Dimethyl Aminomalonates

Several hydroquinolyl alcohols and amines were electrochemically oxidized in methanol in the presence of sodium methoxide and potassium iodide to afford the corresponding intramolecular cyclization products. Furthermore, several amino malonates were electrochemically oxidized to yield the corresponding heterocyclic compounds through an intramolecular carbon–carbon bond formation in the presence of sodium cyanide in methanol.

Stereoselective dehalogenation of (Z)-1-halo-1-alkenyldialkylborane with tributyltin hydride: The behavior of tributyltin hydride as a hydride donor

Abstract The reaction of (Z)-1-halo-1-alkenyldialkylborane (1) with tributyltin hydride (n-Bu3SnH) at 0 °C or room temperature results in reductive removal of the halogen atom to afford (E)- or (Z)-1-alkenyldialkylborane whose stereochemistry depends on the dialkylboryl group and the alkenyl group of 1.