Taiichi Ohra

Diastereoselective total synthesis of (-)-solavetivone via a copper-catalyzed conjugate addition of Me3Al to a cyclohexa-2,5-dienone intermediate

Abstract We succeeded in a stereoselective total synthesis of (-)-solavetivone 1 by employing a new enantioselective copper-catalyzed conjugate addition of Me3Al to a chiral cyclohexadienone 4, which was prepared from a chiral cyclopropane derivative 9 by using a regioselective Hg(II)-mediated cyclopropyl ring-opening reaction, subsequent Pd(II)-mediated spiroannulation of the resulting alkylmercury chloride 8, and a stereoselective Pd(0)-mediated hydrogenolysis of an allylic formate 15 c as the key reactions.

A diquinane synthesis using a novel cation radical-mediated intramolecular [3+2] cycloaddition of cyclopropyl sulfides

Abstract Cyclopropyl sulfides 2 bearing a benzylidene moiety are effectively transformed into diquinanes by treatment with tris-(4-bromophenyl)aminium hexachloroantimonate, as a single-electron oxidant, in dichloromethane at room temperature. This [3+2] cycloaddition reaction requires benzylidene moieties as a CC double bond component.

Tandem oxidative ring cleavage–cyclisation reactions of cyclopropylsulfides: a novel synthesis of cyclic ethers

Treatment of cyclopropylsulfides bearing a hydroxy group in the side chain with ceric ammonium nitrate in methanol gives five- or six-membered cyclic ethers via a tandem cation radical ring cleavage–cyclisation sequence.

Total synthesis of (–)-solavetivone using enantioselective copper-catalysed conjugate addition of Me3Al to a cyclohexa-2,5-dienone intermediate

By applying a new enantioselective Cu-catalysed conjugate addition of Me3Al, (–)-solavetivone 1 is synthesized stereoselectively from cyclohexa-2,5-dienone 4, prepared from a chiral compound 6 using a regioselective HgII-mediated cyclopropyl ring-opening, subsequent PdII-mediated spiroannulation of 7, and a stereoselective Pd0-catalysed hydrogenation of an allylic formate 5 as key reactions.

A sulfur-assisted regioselective α-functionalization of cyclopropyl sulfides. Synthetic applications of homoallyl anion synthon

γ,δ-Unsaturated γ-sulfenyl or sulfinlalkylmercury chlorides 5 and 15, generated from the cyclopropyl sulfide 7 and mercury (II) trifluoroacetate, were demonstrated to be homoallyl anion synthons; these compounds recyclized into the α-functionalized cyclopropyl sulfide on reaction with several electrophiles.

Novel asymmetric cyclopropanation utilizing sulfinyl chirality : application to construction of a spiro[4.5]decane system

An optically active vinylic sulfoxide is stereoselectiviely transformed into a chiral cyclopropane by means of a Michael addition reaction with an allyl Grignard reagent, and using this novel cyclopropanation, assmmetric construction of a spiro [4.5] decane is achieved.