Hirosuke Yoshioka

Highly selective ring opening of epoxides with silicon tetrafluoride: preparation of fluorohydrins

Abstract Regio-, stereo-, and chemoselective transformation of epoxides into fluorohydrins with silicon tetrafluoride is described.

Sesquiterpene lactones and diterpenoids from Helianthus argophyllus

Abstract Three germacranolide sesquitepene lactones (argophyllin-A and -B and eupatolide), three diterpenoids (ciliaric acid, (−)-16-α-hydroxy-kaur-11-en-19-oic acid and (−)-16-α-hydroxykaurane) and one flavonoid (nevadensin) were isolated and characterized from a chloroform extract of Helianthus argophyllus. Argophyllin-A and -B are both described here for the first time. Their structures were deduced by 1H NMR and 13C NMR. Argophyllin-A and -B were found to show anti-auxin effects while eupatolide exhibited weak insecticidal activity.

Chemoselective fluorination for primary alcohols

Abstract Primary alcohols and their silylated derivatives are selectively fluorinated by tetraalkylammonium fluoride and aryl (or alkyl )sulfonyl fluoride.

Regiospecific ring opening of α,β-epoxysilanes with silicon tetrafluoride and application to the synthesis of fluoroalkenes

Abstract α,β-Epoxysilanes undergo the ring opening-fluorination with silicon tetrafluoride in the presence of diisopropylethylamine and water to give β-fluoro-β-silyl alcohols specifically, and the subsequent olefination with potassium hexamethyldisilazide affords fluoroalkenes in good yield.

Chemoselective synthesis of homoallylic fluorides from cyclopropylmethanols by ring opening

Abstract Treatment of cyclopropylmethanols with pyridinium poly(hydrogen fluoride) in chlorobenzene-diisopropylamine in the presence of KHF 2 gave selectively homoallylic fluorides.

Nucleophilic fluorination of chlorinated N-heterocycles with tetrabutylphosphonium hydrogendifluoride and dihydrogentrifluoride

Fluorination of various chlorinated N-heterocycles with tetrabutylphosphonium hydrogendifluoride (1) or dihydrogentrifluoride (2) readily proceeded in high yields under mild conditions

Novel synthesis of monofluorocyclobutanes by the ring expansion-fluorination of cyclopropylmethanols with an amine-metal fluoride-pyridinium poly(hydrogen fluoride)-complex

Various new 1-fluoro-1-alkyl(or aryl)-2-substituted cyclobutanes were synthesized stereoselectively from 1-alkyl(or aryl)cyclopropyl carbinols by the ring expansion-fluorination using (iPr)2-KHF2-(HF)n·Py, and 2-hydroxymethyl-1-fluorocyclobutanes were synthesized via a new rearrangement of (1-alkyl(or aryl)cyclopropyl) ethylene oxides.

Chemistry, Absolute Structures and Biological Aspect of the Most Active Isomers of Fenvalerate and Other Recent Pyrethroids

Abstract A number of stereoisomers of recent pyrethroids having an α-cyano-3-phenoxybenzyl moiety, i.e., fenvalerate, Cypermethrin and fenpropanate could be optionally synthesized from (+)- or (-)-3-phenoxy-mandelic acid and their absolute configurations were determined to be S to the benzylic asymmetric carbon atoms of the most active isomers. Toxicity ratios of the S-isomers to the R-isomers to house fly were generally larger than those to mosquito larva. Relative toxicity of fenvalerate As (S-acid, R-alcohol) to Aα was enhanced in accordance with exposure period of mosquito larva on dipping or tobacco cutworm on dry leaf residue. The late emerging toxicity of the As appears to result from in vivo activation as evidenced by biological assays involving hemolymph exchange and ligature on larvae of cabbage armyworm. Feeding deterrent nature of As was also discussed.

Trichoclin, a new furocoumarin from trichocline incana

Abstract The structure for trichoclin, ( E )-8-(3-methyl-4-hydroxy-2-butenyloxy)-psoralen, a new furocoumarin isolated from Trichocline incana , has been established. Phellopterin and isopimpinellin were also obtained. The new side chain of trichoclin was confirmed by synthesis.

Regiospecific preparation of 2-oxazolines promoted by silicon tetrafluoride

Silicon tetrafluoride promotes reaction of oxiranes with nitriles to give 2-oxazolines in good yield