Kosei Shioji

Reaction of Benzyne with Salicylaldehydes: General Synthesis of Xanthenes, Xanthones, and Xanthols

The reaction of salicylaldehydes with benzyne prepared from o-trimethylsilyphenyl triflate and CsF gave xanthenes and xanthones. When the reaction was carried out under basic conditions, 9-hydroxyxanthenes (xanthols) were obtained in good yields.

Synthesis of bifunctional P-chiral hydroxy phosphinates; lipase-catalyzed stereoselective acylation of ethyl (1-hydroxyalkyl)phenylphosphinates

Abstract Lipase-catalyzed acylation of ethyl (1-hydroxyalkyl)phenylphosphinates afforded a single diastereomer in high enantiomeric excess. The substituent effect of the alkyl group toward the acylation using Candida antractica (CAL) was larger than that of an immobilized lipase from Pseudomonas fluorescens lipase (lipase AK).

Lipase-catalyzed kinetic resolution of P-chiral phosphorus compounds: enantiopreference of Pseudomonas lipase and Candida antarctica lipase

Optically active 1-hydroxymethylalkylphenylphosphine oxides 1a–c were prepared by Pseudomonas fluorescens lipase (lipase AK) and Candida antarctica lipase (CAL)-catalyzed optical resolution. Lipase AK-catalyzed resolution of tert-butyl derivative 1c showed R-selectivity, whereas CAL preferred the S-enantiomer.

Reaction of a cation radical generated from trivalent phosphorus compound through single-electron transfer to arenediazonium salt

A cation radical generated from a trivalent phosphorus compound through single-electron transfer to an arenediazonium salt undergoes both ionic and radical reactions. Relative ease of these reactions depends mainly on the number of phenyl ligands on the phosphorus atom.

Lipase-catalyzed kinetic resolution of racemic seven-membered substituted lactones

Abstract Optically active 3-, 4-, 5-, or 6-methyl substituted seven-membered lactones were prepared by Candida antarctica lipase (CAL)-catalyzed kinetic resolution of the racemic lactones. Among these lactones, only in the case of 5-methylhexanolide ( R )-isomer reacts faster than the other enantiomer, while the rest of lactones show ( S )-selectivity.

An efficient synthesis of (R)-(+)-recifeiolide and related macrolides by using enantiomerically pure (R)-(−)-5-methyl-2,2,2-triphenyl-1,2λ5-oxaphospholane

Abstract E-(R)-(+)-8-Dodece-11-olide, which is known as recifeiolide, was synthesized by a six-step reaction starting from (R)-(+)-propene oxide in a total yield of 53 %. The key step of this synthesis is the preparation of (R)-(−)-methyl 11-hydroxy-8-dodecenate using (R)-(−)-5-methyl-2,2,2-triphenyl-1,2λ5-oxaphospholane. Be using this method, enantiomerically pure 13- and 14-membered macrolides were also synthesized.

Novel Formation of 1,2-Dithiolane-3-thione from β-Dithiolactone

The sulfurization of (3-dithiolactone gave l,2-dithiolane-3-thione via an ionic intermediate. The reaction of 1,2-dithiolane-3-throne with acetylenedicarboxylate esters gave the corresponding spirocyclic 1,3-dithioles in good yields, whereas the reaction of 5-methyl-l,2-dithiole-3-thione with DMAD afforded a 1:2 cycloadduct in 78% yield.

Reaction of 3,3,5,5-Tetramethylthiolane-2,4-dithione with Benzyne: Novel Formation of Benzodithiole

Reaction of 3,3,5,5-tetramethylthiolane-2,4-thione with benzyne gave a new type of benzodithiole in 78% yield. Dithioesters thiocarbonyl group initially attacked benzyne to afford the corresponding betaine, which finallyrearranged to give benzodithiole. On the other hand, reaction of cyclic dithiolactone with benzyne recovered the starting dithiolactone in almost quantitatively.

SYNTHESIS OF C1–C6 FRAGMENT FOR EPOTHILONE A VIA LIPASE-CATALYZED OPTICAL RESOLUTION

Synthesis of 5-oxo-(3S)-hydroxy-4,4-dimethylheptanoic acid (1), C1–C6 fragment of epothilone A, is described. Racemic tert-butyl 5-oxo-(3S)-acetoxy-4,4-dimethylheptanoate (5) was prepared by acylation of enamine followed by aldol condensation. Optical resolution of the heptanoate 5 was carried out by lipase catalyzed hydrolysis (yield 50%, > 98% e.e.).

Novel ring contraction of dioxepanes to tetrahydropyrans. Reaction of dioxepanes with trimethylsilyl trifluoromethanesulfonate

Reaction of 5-methylene-1,3-dioxepanes derived from oxaphospholanes and paraformaldehyde with trimethylsilyl trifluoromethanesulfonate in the presence of a base yielded novel, exo formyl tetrahydropyran derivatives in good yields.