Akira Yoshikoshi

Organoselenium-mediated reduction of α,β-epoxy ketones to β-hydroxy ketones: A new access to inter- and intramolecular aldols

Abstract The organoselenium-mediated reduction of α,β-epoxy ketones has been demonstrated to be a promising entry to a variety of cyclic and acyclic aldols.

Sodium phenylseleno(triethoxy)borate, Na+(PhSeB(OEt)3]−: The reactive species generated from (PhSe)2 with NaBH4 in ethanol

The reactive species generated from (PhSe)2 with NaBH4 in ethanol has been demonstrated to be a sodium phenylseleno(triethoxy)borate complex, Na+[PhSeB(OEt)3]−, as evidenced in the reduction of α,β-epoxy ketones leading to β-hydroxy ketones.

Cycloaddition of isopropylcyclopentadienes and dichloroketene, and the solvolysis of the adducts : Synthesis of β-thujaplicin (hinokitiol)

Abstract Dichloroketene was allowed to react with a mixture of 1- and 2-isopropylcyclopentadienes (1 and 2) to afford a mixture of the cycloadducts 5, 7 and 8. The adducts 5 and 8 were isolated, and an adduct 7 was obtained as a mixture with 5. The structures of these adducts were assigned. Some derivatives of the adducts were prepared and their structures discussed. A mixture of β- and γ-thujaplicins (19 and 20) were produced after a mixture of the adducts was heated in acetic acid containing potassium acetate, 2-Isopropylcyclopentadiene (2) was prepared from cyclopentadienylmagnesium bromide and isopropyl tosylate, and the adduct obtained gave only β-thujaplicin under the same solvolytic reaction conditions.

Stereoselectivity in the sigmatropic rearrangement of eight- and nine-membered cyclic allylsulfonium ylides. synthesis of vinyl- substituted butyro- and valerolactones

Abstract The rhodium (II) acetate-catalyzed [2,3]sigma-tropic rearrangement of the diazo malonates of ( z )-4-phen-ylthio-2-buten-l-ol derivatives 6 afforded vinyl-substituted butyrolactones 10 in a highly stereoselective manner, while the rearrangement of the diazo malonates of homologues, ( z )-5-phenylthio-3-penten-1-ol derivatives 9, yielded vinyl-substituted valerolactones 13 and 14 in the predominance of the formers. A stereochemically fixed substituent R in 9 was found to be an important factor resulting to high stereoselectivity in the latter rearrangement as shown by using diazo malonate 20b as substrate.

Stereoselective synthesis of contiguously substituted butyrolactones based on the cyclic allylsulfonium ylide rearrangement

α-Diazomalonates of (Z)-4-phenylthio-2-buten-1-ol homologues (2) stereoselectively provided γ-alkyl-α-ethoxycarbonyl-α-phenylthio-β-vinylbutyrolactones (1) by the [2.3]sigmatropic rearrangement of cyclic sulfonium ylides (3) intramolecularly generated therefrom with rhodium acetate.

Interconversion between hibaene and kaurene

Abstract Hibaene-α-epoxide, upon treatment with BF 3 -etherate in benzene, undergoes skeletal rearrangement into the kaurane ring system, giving an unsaturated alcohol or a glycol, respectively. The unsaturated alcohol, after conversion to the corresponding unsaturated ketone, affords kaurane, isokaurene, and kaurane by Huang-Minlon reduction. It has also been found that an equilibrium mixture of kaurene, isokaurene and hibaene, in the ratio of 2:3:5, is produced when either kaurane or hibaene is heated in boiling xylene in the presence of iodine; thus the interconversion between hibaene and kaurene has been achieved. The stereochemistry of the intermediates in the transformation of hibaene to kaurene has been established.

Synthetic studies on spider neurotoxins (I): total synthesis of nephilatoxins (NPTX-9) and NPTX-11), new neurotoxins of Joro spider (Nephila clavata)

Abstract The first and efficient synthesis of Nephilatoxins (NPTX-9 and NPTX-11), new neurotoxins of Joro spider ( Nephila clavata ), has been achieved by employing a key azide intermediate as the polyamine unit.

New access to dl-paniculide using α-phenylthio-β-vinylbutenolide as synthetic block

Abstract A new synthetic approach to dl -paniculide A (1) based on the annulation of 2-formylpropionate with α-phenylthio-β-vinylbutenolide 4 is described. The annulation products 6a–6c was dehydrated to give 7 , and the sulfoxide of 7 was submitted to sulfoxide-sulfinate rearrangement in aqueous media to yield 8a and 8b . The latter was converted to the former by configurational inversion of its hydroxyl group. Saturated lactone 11a obtained from 8a was homoprenylated, and after desilylation, the product 12b was selenenylated to give 13a . Alkaline hydrolysis followed by oxidative elimination of the selenenyl group provided 14a , which was then acetylated and oxidized with lead tetraacetate to yield 15a and 16a–16c . dl -Paniculide A was derived from 15a and 16a via 18a .

Sesquiterpenoids of vetiver oil—I: The structures of zizanoic acid and related constituents

Abstract Two sesquiterpene car☐ylic acids, zizanoic and epizizanoic acids, were isolated from the essential oil of vetiver and were assigned the structures1a and2a on the basis of chemical degradation. Although khusimol and zizaene (tricyclovetivene) had been assigned structures previously, the current work revealed that these sesquiterpenoids also belong to the zizaane group and that the formulae should be revised as1b and1c, respectively.

Chemoselective reduction of an α,β-epoxy ketone moiety coexisting with an enone function

The chemoselective reduction of an α,β-epoxy ketone moiety coexisting with an enone function has been efficiently achieved with an organoselenium reagent Na+[PhSeB(OEt)3]−.