Takuzo Hisano

[3,3]-sigmatropic rearrangement of allylic xanthates in β-cyclodextrin complexes

Abstract The inclusion complex of O -cinnamyl S -methyl dithiocarbonate (xanthate) wtih β-cyclodextrin (β-CD) undergoes remarkably accelerated [3,3]-sigmatropic rearrangement to give the optically active dithiol ester in good yield with an enantiomeric excess (3.3.) of 46 %.

Effects of benzimidazoles on mouse and rat limb bud cells in culture

Benzimidazoles exhibited an inhibitory action on the chondrogenesis in a mouse limb bud cell culture system; further, nitro and chloro groups at the 5 position in 2-(2-pyridyl)benzimidazole were found to be potent substituents. However, 2-(2-pyridyl)benzoxazole and 5-methoxy-2-(2-pyridyl)benzothiazole exhibited no inhibitory action under our experimental conditions. Thus, imidazole NH proton seemed to be important in the inhibitory action in the mouse cell system. The concentrations of thiabendazole (TBZ), 5-hydroxy-TBZ (5-HY-TBZ) and N-methyl-TBZ necessary to reduce the amounts of cartilage proteoglycan by 50% (TP50) were estimated to be about 0.35, 0.25 and 0.70 mM, respectively, in the rat limb bud cell culture system. The TP50 of TBZ and 5-HY-TBZ in the rat cell system were 3- to 4-fold higher than those in the mouse cell system.

A convenient and stereoselective synthesis of allylic sulfides

Abstract The fractional distillation of 0-(2-alkenyl or 2-cycloalkenyl) S-alkyl dithiocarbonates (xanthates) affords 2-alkenyl or 2-cycloalkenyl alkyl sulfides. The reaction involves the [3,3]-sigmatropic rearrangement of the xanthates to produce S-(2-alkenyl or 2-cycloalkenyl) S-alkyl dithiocarbonates followed by extrusion of carbon oxysulfide to give 2-alkenyl or 2-cycloalkenyl alkyl sulfides.

Reaction of aromatic N-oxides with dipolarophiles. XVII. Cycloaddition behavior of allenes toward pyridine N-oxides and formation of azetidine-type cycloadduct

3,5-Dimethylpyridine N-oxide was allowed to react with phenylsulfonylpropadiene in CHCl 3 at room temperature to give a mixture of the 1:1 [1,5] sigmatropic rearrangement product and the 1:2 azetidine-type cycloadduct. The structure of the azetidine-type cycloadduct was determined by single crystal X-ray analysis. The reaction behavior and the regioselectivity are discussed in terms of the frontier molecular orbital considerations

A simple one-pot synthesis of hydroisobenzothiophenes via three-step sequential pericyclic reactions of xanthates

Abstract Thermolysis of O -(2,4-alkadienyl) S -(2-alkenyl or 2-alkynyl) dithiocarbonates (xanthates) gave the hydroisobenzothiophene derivatives via two sequential [3,3]-sigmatropic rearrangement followed by the intramolecular cycloaddition.

Reaction of aromatic N-oxides with dipolarophiles. IXI: PM3 analysis of sequential pericyclic reactions between pyridine N-oxides and allenes

Sequential pericyclic reactions between pyridine N-oxides and allenes were evaluated in terms of PM3 calculation. Structures corresponding to the perturbating system were calculated by varying the distance of the addends. The cycloaddition occurs via π-complex. In the transition structure TS1 of primary cycloaddition, the lengths of the newly created bonds of O-C and C-C are 1.864 and 2.204 A, respectively. The bond between the O atom of pyridine N-oxide and the central carbon of allene is ca. 35% formed at TS1, slightly advanced than the other (ca. 30%). The PM3 calculation at the UHF level predicts that [1,5]-sigmatropic rearrangement of the primary cycloadduct proceeds via a transition state with a biradical character

Molecular structure of the double Diels–Alder cycloadduct of 2-pyrone and cycloocta-1,5-diene. Very close intramolecular H/H contact and some comments

The molecular structure of the double Diels–Alder adduct (DDA) of 5-methoxycarbonyl-2-pyrone and 1,5-cyclooctadiene has been clarified by single crystal X-ray analysis on the phenylurethane of the hydroxymethyl derivative obtained from LiAlH4 reduction of the DDA adduct. The X-ray analysis indicates that the DDA adduct has very close non-bonded H/H contacts of ca. 1.94 A. The observed data are compared with those derived from the MM- and MO-optimized structures.

Reaction of aromatic N-oxides with dipolarophiles. Part 18. Formation mechanism and X-ray structure of the cycloadduct from sequential pericyclic reaction of pyridine N-oxides with phenylsulfonylallene

Sequential pericyclic reactions of pyridine N-oxides (1) with phenylsulfonylpropadiene (2) and 1-phenylsulfonylpropyne (3) were investigated. 3,5-Dimethylpyridine N-oxide (la) was allowed to react with 2 in CHCl3 at room temperature to give a mixture of the [1,5]-sigmatropic rearrangement product (4a) of the 1 : 1 cycloadduct and the 1 : 2 azetidine-type cycloadduct (5a). The structure of 5a was established by single crystal X-ray analysis. The reaction rate of 1a with 2 was about 50 000 times that of 1a with N-phenylmaleimide. The reaction of 1a with 3 did not give 5a but 4a as the sole product. The reactivity, regio- and peri-selectivity and formation mechanism of 4 and 5 are discussed in terms of the frontier molecular orbital consideration based on kinetic and molecular orbital calculation data.

Sequential pericyclic reactions of unsaturated xanthates. One-pot synthesis of hydrobenzo[c]thiophenes

O-Alka-2,4-dienyl S-(alk-2-ynyl or alk-2-enyl) dithiocarbonates (xanthates) underwent [3,3]sigmatropic rearrangement to give the dithiol esters which, on heating, extruded carbon oxysulfide (COS) to give the allylically rearranged sulfides which then underwent intramolecular Diels–Alder cycloaddition to give hydrobenzo[c]thiophenes. Lewis acids catalysed the extrusion and intramolecular cycloaddition reactions, in which the reactivity and endo-selectivity were remarkably enhanced. The structures of the cycloadducts were determined on the basis of the X-ray structure of a hydrobenzo[c]thiophene.Based on these findings together with MO calculation data, the observed reaction behaviours are discussed in terms of frontier molecular orbital considerations.

Cycloaddition reaction of 4-oxo-4H-pyrazole 1,2-dioxides with epoxynaphthalene. X-ray analysis of the cycloadduct and some comments on cycloaddition behavior

The crystal structure of the cycloadduct of 2,5-bis(methoxy- carbonyl)-4-exo-4H-pyrazole 1,2-dioxide with epoxynaphthalene was elucidated. The result indicates that the cycloadduct resulted from the direct 1,3-dipolar cycloaddition