Masaru Tada

Tetranortriterpenoids from Azadirachta indica

Abstract Azadirachta indica afforded two novel tetranortriterpenoids by gravity column chromatography. Their structures were elucidated by extensive 1D and 2D NMR techniques.

A diterpene from Bidens pilosa

A new diterpene, phytyl heptanoate, has been isolated from Bidens pilosa, and its structure confirmed by chemical synthesis.

Photocycloaddition of Δα,β-γ-butyrolactone with olefins and its quenching by dimethoxyethylene

Abstract Photocycloaddition of Δ α,β -γ-butyrolactone ( 1 ) to cyclopentene or cyclohexene giving cyclobutane derivatives 4 and 5 proceeds through the triplet excited state of lactone 1 . The cycloaddition is quenched by dimethoxyethylene, and the formation of exciplex between 1 and dimethoxyethylene is proposed for the mechanism of the quenching.

Smiles-type free radical rearrangement of aromatic sulfonates and sulfonamides: syntheses of arylethanols and arylethylamines

Smiles-type free radical rearrangements of arenesulfonates and arenesulfonamides are exploited for synthetic purposes. 4-Substituted benzenesulfonates cause Smiles-type rearrangement only when substituted by an electron withdrawing group. Therefore, ipso-attack by an alkyl radical on arenesulfonates takes place in an electrophilic manner. Arenesulfonamides rearrange only when the amide nitrogen is substituted by an alkoxycarbonyl group, due to the electron withdrawing nature of this group. Sulfonates and the N-ethoxycarbonylsulfonamide derivatives of naphthalene, quinoline, and thiophene cause more rearrangement and show synthetic utility. Aromatic amino acid analogues were synthesized by Smiles-type rearrangement with moderate yields. The radical Smiles-type rearrangement of sulfonate and sulfonamide derivatives can be a useful synthetic route when we understand the electronic character of these reactions.

Acyl migration in 2-substituted-2-acylpropyl radicals. The reaction of organocobaloximes as mimicries of coenzyme-B12

Abstract Radical cleavage of the carbon—cobalt bond of 2-acetyl-2-methoxy-carbonylpropyl cobaloxime ( 1 ) and 2-benzoyl-2-phenylpropyl cobaloxime ( 5 ) gives the enones which are formed by the 1, 2-migration of acyl-group.

Synthesis of (3-Furanyl) Methyl Derivative

Abstract 3-Methylfuran is an important building block of terpenoid compounds1) and some of these compounds are biologically active, for example as a defence substance of animal.2) Though many methods have been developed for the syntheses of 3-substituted furan derivatives,3) most of them lack the generality as a synthetic method of (3-furanyl) methyl derivative. Tannis has recently reported the construction of 3-substituted furan derivative by using 3-(lithiomethyl) furan or 3-(chloromagnesium methyl) furan, and demonstrated the generality of his method.4)

The interaction between cobalt(II) complexes and sulphur compounds studied by ESR spectroscopy

Abstract ESR analyses of bis-dimethylglyoximato(pyridine)cobalt(II) and bis-diphenylglyoximato(pyridine) cobalt(II) complexes show the formation of six-coordinated 19-electron complexes. Tetrahydrothiophene and γ-butyrothiolactone can coordinate to those cobalt(II) complexes as sixth ligands. Hyperfine splittings (ACo) of the sulphur coordinated complexes are larger than the corresponding pyridine coordinated complexes. Five-membered sulfide and thiolactone coordinate efficiently to the five-coordinated Co(II) complexes, whereas acyclic analogs do not coordinate. ACo values and those structural requirements for the sulfur ligands are accounted for by contribution of the back donation from cobalt(II) to sulphur. A possible mechanism in which a Co(II) species is coordinated with a thioester group is proposed for the coenzyme-B12 mediated isomerization of methylmalonyl-CoA.

Charge 3ransfer from donor to photoexcited Ru(bpy)32+ in solution and polymer matrix

Electron transfer quenching of photoexcited Ru(bpy) 3 2+ (bpy, bipyridine) by three kinds of hole transport material, phenothiazine (PTZ) and 10-methylphenothiazine (MPTZ) was studied in acetonitrile solution and a polymer film. The quenching rate constants (k q ) with respect to ΔG in acetonitrile solution are discussed in terms of Marcus theory. In poly(ethyleneoxide) (PEO) films, quenching of photoexcited Ru(bpy) 3 2+ was observed and analysed by a static quenching model. The electron transfer distance in the polymer film was found to be 1.1-1.9 nm using a modified Perrin equation considering the excluded volume effect. The dependence of the electron transfer rate on ΔG in the PEO film was larger than that in acetonitrile solution.

Intramolecular radical substitution on the sulfur of thioester, sulfide, sulfoxide, and sulfone

Abstract Alkyl radicals having the sulfur functions such as thioester, sulfide, and sulfoxide at the γ-position gave five membered cyclic thiolactone, sulfide and sulfoxide, while sulfone did not react with the alkyl radical. The product expectad from the sulfuranyl radical intermediate, which can pseudo-rotate, was not obtained.

Synthesis and spectroscopic properties of 1-azamkthanocyclopentacycloundecene ring systems☆

Abstract Novel 1-aza-6,11- and 1-aza-4,9-methnocyclopentacycloundecene ring systems were synthesized by the reaction of 3,8-methano[11]annulenone with N-(1-phenylvinylimino)triphenylphosphorane followed by dehydrogenation. These compounds are diatropic as 14pielectron vinylogues of 1-azaazulene.