Katsuo Ohkata

Synthesis and chemical behaviors of 12-substituted dibenz[c,f][1,5]azastibocine and dibenz[c,f][1,5]azabismocine derivatives: evidences of 10-Pn-4 type hypervalent interaction

Abstract A series of 12-substituted 6-methyl-5,6,7,12-tetrahydro-12-X-dibenz[c,f][1,5]azastibocine (1) and azabismocine (2) were prepared. Both 1 H and 13 C NMR signals of the N-methyl group were shifted to downfield by electron-withdrawing substituent at the pnictogen atoms and the shift was linearly correlated with Hammett σ m values.

Stereoselective formation of activated cyclopropanes with pyridinium ylides bearing a (−)-8-phenylmenthyl group as the chiral auxiliary

Abstract The reaction of various mono-substituted methylidenemalononitriles with (−)-8-phenylmenthyl α-pyridiniumacetate in the presence of base afforded the corresponding dicyanocyclopropane compounds with exclusive trans -selectivity and good diastereoselectivity (up to 86:14). The stereochemistry of the major products were determined to be of 1 R configuration by X-ray structural analysis of the crystalline trans -2,2-dicyano-3-(4-pyridyl)cyclopropanecarboxylate. The geometric and diastereofacial selectivities were rationalized assuming anti -periplanar approach in the open-chain model, followed by epimerization and then cyclization to give the cyclopropane compounds.

Efficient synthesis of a 4,5-epoxy-2-cyclohexen-1-one derivative bearing a spirolactone via a Diels–Alder reaction with high π-facial selectivity: a synthetic study towards scyphostatin

The Diels-Alder reaction of spirolactones with cyclopentadiene afforded the adduct with high pi-facial selectivity; a hydrophilic analogue of scyphostatin was synthesized from the Diels-Alder adduct.

Construction of the Adamantane Core of Plukenetione-Type Polycyclic Polyprenylated Acylphloroglucinols

The construction of a highly functionalized adamantane core of plukenetione-type polycyclic polyprenylated acylphloroglucinols (PPAPs) is described. The method features the construction of the bicyclo[3.3.1]nonane core (3) by successive Michael reactions and the construction of the adamantane core of plukenetione-type PPAPs by acid-catalyzed cyclization of a bicyclo[3.3.1]nonane precursor (2).

Stereoselective cyclopropanation of 3-aryl-2-phosphonoacrylates induced by the (−)-8-phenylmenthyl group as a chiral auxiliary

The cyclopropanation of (−)-8-phenylmenthyl (E)-3-aryl-2-phosphonoacrylates with dimethyloxosulfonium methylide and diazomethane afforded the corresponding trans cyclopropane derivatives with high diastereoselectivity as the major diastereomer. The high selectivity is understandable in terms of the π–π interaction between the phenyl ring of the chiral auxiliary and the acrylate moiety.

Asymmetric darzens condensation of ketones with α-chloroacetates by means of (–)-8-phenylmenthyl auxiliary

The Darzens condensation of symmetric and unsymmetric ketones with (–)-8-phenylmenthyl α-chloroacetate diastereoselectively affords glycidic esters in 77–94% de; the stereochemistry [(2R,3R) configuration] of the product is understandable in terms of π–π interaction in the open transition state model.

Transannular bond formation between the antimony and the nitrogen atoms in dibenz[c,f][1,5]azastibocine system. Formation of XSbX and XSbN+ hypervalent bond

6-Methyl-5,6,7,12-tetrahydro-12-p-tolyldibenz[c,f][1,5]azastibocine (1) was prepared by means of one-pot reaction of di(o-bromobenzyl)methylamine (2), butyllithium, and antimony trichloride, followed by p-tolyllithium in 23% yield. Halogenation of 1 afforded the corresponding dihalide (4a–c and 5d) and the reaction of 4b and 4c with SbCl5 or AgBF4 resulted in the formation of XSbN+ bond (5b,c).

Loliolide and Other Germination Inhibitory Active Constituents in Equisetum Arvense

Abstract (-)-Loliolide (1) showing an inhibitory activity for lettuce seed germination was isolated from leaves of Equisetum arvense. It is rare that this active compound occurred from the family Equisetaceae.

Formation of ammoniophosphoranes by transannular interaction in dibenz[c,f][1,5]azaphosphocine system

Dibenz[c,f][1,5]azaphosphocine 12-oxide derivatives (1a, 3) and their related compounds were prepared and NMR spectral change of these samples by the addition of SOCl2 or t-BuMe2SiOTf are reported. The NMR parameters (1H and 31P) are consistent with bicyclic phosphoranes for at least 1a′ and 3′, each contains a transannular hypervalent ClPNMe bond.

Highly asymmetric induction in the Diels-Alder reaction of 3-alkoxycarbonyl-substituted coumarin

Abstract The essentially complete (>99%) asymmetric Diels-Alder reactions were achieved between 3-(8-phenylmenthyloxycarbonyl)coumarin ( 1c ) and 1,3-butadienes ( 2a–c ) in high chemical yields.