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Coenzyme PQQ is demonstrated to catalyse the oxidative Cα–Cβ fission (dealdolation) of β-hydroxy amino acids under very mild conditions.

VO(OEt)Cl 2 oxidized 2-phenylglycine derivatives via oxidative deamination and/or decarboxylation giving ethyl benzoate and ethyl phenylglyoxylate.

2-Phenylethnylpyridine reacted with dimethyl acetylenedicarboxylate (DMAD) in the presence of a proton source such as an alcohol to give Indolizines having methoxycarbonyl groups at the 2- or 2,3-positions in high yields.

Diketene undergoes a VO(OR)Cl2-induced cyclization with styrenes via ring opening to give 3-alkoxycarbonyl-2-methyl-5-phenyl-4,5-dihydrofurans. Desilylative aromatization to the furans is observed in the reaction with α-triemthylsilylstyrene.

3-Cyano-2-(phenylethynyl)pyridine (1) was cyclized intramolecularly under acidic conditions to give 1,6-naphthyridin-5(6H) one (2) and 5H-pyrano[4,3-b]pyridin-5-one (4). Pyranopyridine 4 was readily transformed to 2 or naphthyridinone 9 having an alkyl substituent at 6-position

Molybdenum pentachloride induced the ring-opening reactions of cyclopropyl phenyl ketone or propyl 2-(trimethylsilylmethyl)cyclopropanecarboxylate to give 1-phenyl-1,2,4-trichloro-1-butene or cis-2-chloro-4-pentanolide, respectively.

The MnTPPCl-catalyzed epoxidation of olefins with hydrogen peroxide is efficiently enhanced by mediation of orthequinones.

An oxovanadium compound obtained from VO(OEt)Cl2 and AgOTf or MesSiOTf efficiently induced dehydrogenative aromatization of α,β-unsaturated cyclohexenones to give aryl ethyl ethers in good yields.

Hitherto unknown or rarely reported sulfur-containing bicyclic β-lactams, 6-and 7-thianonanams, were synthesized by addition of sulfur dichloride to N-allyl-β-styryl-β-lactam

An oxo group is introduced at the allylic position of 3-methyl-2-cyclopenten-1-one and β-ionone on treatment with VO(OR)Cl 2 in ROH. VO(OR)Cl 2 induces γ-alkoxylation in the case of 2-cyclopenten-1-one. Reaction of 1-acetyl-1-cyclohexene with VO(OEt)Cl 2 results in γ-alkoxylation and/or aromatization to give 1-acetyl-3-ethoxy-1-cyclohexene and the corresponding aromatic.

The title compound (5) was synthesized by silica gel assisted cyclization of 2-phenylethynylpyridine-3-carboxylic acid (3). It was also synthesized from 3-cyano-2-phenylethynylpyridine (6) in good yield by basic cyclization processes

The reactions of coenzyme PQQ (pyrroloquinolinequinone) and several amino acids have been investigated in vitro. PQQ catalyses the oxidative decarboxylation of α-amino acids to afford the corresponding aldehydes under aerobic conditions. During the catalytic cycles, PQQ is gradually converted into oxazolopyrroloquinoline (OPQ) derivatives to be deactivated. Product analyses indicate that the reaction proceeds via an ionic mechanism that involves a carbinolamine-type adduct as a key intermediate. From this intermediate, direct decarboxylation (major path) and dehydration followed by decarboxylation and hydrolysis or by intramolecular cyclization (minor paths) competitively occur to give the quinol, the aminophenol and the OPQ derivative, respectively. In the reactions with β-hydroxy amino acids, tyrosine and tryptophan, oxidative dealdolation (Cα–Cβ fission) proceeds effectively. The similar ionic mechanism that involves the carbinolamine-type intermediate is suggested by the product analyses under both aerobic and anaerobic conditions.

An efficient catalytic system for the palladium(II)-induced regioselective ringopening oxidation reaction of α,β,-epoxysilane was achieved by use of trimethyl ester of coenzyme PQQ under molecular oxygen. The redox cycle of the ester was performed with two different oxidation states of vanadium compounds, VCl2 and VO(OEt)3.

Selective functionalization of 1H-pyrrolo[2,3-b]pyridine (7-azaindole) at the 6-position was achieved by Reissert-Henze type reaction. Thus, halogeno (Cl, Br, I), cyano and thiocynato groups were directly introduced to the pyridine ring of 7-azaindole

An efficient system for the catalytic epoxidation reaction of olefins with molecular oxygen was achieved by utilization of FeCl2 or Co(OAc)2 and the N-heterocyclic podand ligand, N,N′-bis{2-(4-imidazolyl)ethyl}-2, 6-pyridine-dicarboxamide (BIPA), without the need for a coreductant. The multidentate coordination of BIPA is considered to serve an important role in the oxygenation.

Silyl enol ethers underwent the VO(OR)Cl2-induced homo- or cross-coupling giving 1,4-diketones selectively via one-electron oxidative desilylation.

Functionalization of 1H-pyrrolo[2,3-b]pyridine (7-azaindole) was studied to provide new compounds directing toward agrochemicals and/or functional materials. Amino groups such as NH2, NH(CH2)2NH2, and NH(CH2)2NH(CH2)2NH2 were introduced onto 6-position of 7-azaindole to form multidentate agents. 6-Amino and 6-iodo derivatives were easily converted to podant-type compounds, N,N′-bis(1H-pyrrolo[2,3-b]pyridin-6-yl)-1,3-benzenedicarboxamide and bis(1H-pyrrolo[2,3-b]pyridin-6-yl)acetylene, respectively. Polyacetylene having 1H-pyrrolo[2,3-b]pyridyl group as a pendant was obtained by polymerization of 6-ethynyl-7-azaindole synthesized by ethynylation of 6-bromo derivative. As functionalization at 3-position of 7-azaindole, syntheses of 3,3′-selenobis[1H-pyrrolo[2,3-b]pyridine] and the corresponding 3,3′-thio compound, as well as 3-carboxyethenyl- and 3-vinyl-7-azaindoles were performed. Some of these products exhibited high fungicidal activity.

VO (OR) Cl2 is revealed to be a Lewis acid with one-electron oxidation capability. The regioselective ringopening oxygenation of cyclic ketones is catalyzed by VO (OEt) Cl2 in ethanol under oxygen to give the diesters or keto esters. The presence of α, β carbon-carbon double bond in the ketones alters the reaction course. 2-Cyclohexen-l-ones undergo dehydrogenative aromatization to give aryl ethers. An oxovanadium compound obtained from VO (OEt) Cl2 and AgOTf or Me3SiOTf works more efficiently. In the cases of 2-cyclopenten-1- ones, 1-acetyl-1-cyclohexene, and β-ionone, allylic oxidation is achieved to introduce an oxo or alkoxyl group at the γ-position. 2-Phenylglycine derivatives are transformed to ethyl benzoate and ethyl phenylglyoxylate by the VO (OEt) Cl2-induced' oxidative deamination and/or decarboxylation. The ring-opening addition of cyclobutanone to olefins bearing an electron-withdrawing group leads to the corresponding E-chloro ester via oxidation of a cyclobutoxide intermediate. Treatment of a mixture of diketene and styrenes with VO (OR) Cl2 gives 3-alkoxycarbony1-2-methyl-5-phenyl-4, 5-dihydrofurans.Oxidative desilylation is selectively realized by one-electron oxidation of organosilicon compounds with VO (OEt) Cl2. Silyl enol ethers undergo the oxidative cross coupling to afford unsymmetrical 1, 4-diketones. Allylic silanes also regioselectively dimerize to 1, 5-hexadienes. Oxidative desilylation of silyl enol ethers and allylic silanes selectively gives γ, δ-unsaturated ketones depending on their redox potentials.The highly stereoselective monodebromination of gem-dibromocyclopropanes is induced or catalyzed by a low valent vanadium species generated from vanadium (III) chloride or CpV (CO) 4 and zinc in dimethoxyethane in a combination with diethyl phosphonate or triethyl phosphite.

Reductive deconjugation of α-bromo α,β-unsaturated esters was performed by DP(O)(OEt)2 or P(OEt)3–H2O in the presence of triethylamine from mechanistic viewpoint and was applied to the synthesis of a precursor of (±)-patulolide A.

2, 2-Dichlorocyclobut-3-enones undergo VO(OEt)Cl2-induced ring-opening oxidation in ethanol to give ethyl 2,4,4-trichlorobut-3-enoates regioselectively.

A ring enlargement reaction of a diaziridinone was investigated as a possible method for synthesizing heterobicyclic compounds having a bridgehead nitrogen atom. One of the products was transformed to a mesomeric betaine. Thus, the reaction of N,N'-di-tert-butyldiaziridinone (1) and deprotonated pyrrole-2-carboxaldehyde gave 2,3-di-tert-butyl-1-hydroxy-1,2,3,4-tetrahydropyrrolo[1,2-d] [1,2,4]-triazin-4-one (4) in good yield. Similarly, (1) was treated with deprotonated imidazole-2-carboxaldehyde to afford the corresponding imidazo[1,2-d][1,2,4]-triazine derivative (5). Under similar conditions, pyrrole-2-carbonitrile gave an acyclic 1:1 adduct, 1-(N,N'-di-tert-butylcarbazoyl)-2-cyanopyrrole (8), which was successfully cyclized under acid catalysis to 2,3-di-tert-butyl-1-imino-1,2,3,4-tetrahydropyrrolo[1,2-d] [1,2,4]triazin-4-one (9) and the de-tert-butylated product (10). A novel mesomeric betaine 2-tert-butylpyrrolo[1,2-d][1,2,4]triazinium-4-olate (11), was obtained along with its isomer (12) by acidic de-tert-butylation of (4)

Cinnamyltrimethylsilane underwent desilylation via one-electron oxidation with VO(OEt)Cl 2 , which was applied to the cross-coupling with the less oxidizable allylic silanes to give the corresponding 1,5-hexadienes. Chlorination or aromatization based on desilylation was observed on treatment of benzyltrimethylsilane or 3- ethoxycarbonyl-2-methyl-5-trimethylsilyl-5-phenyl-4,5-dihydrofuran with VO(OEt)Cl 2 -Me 3 SiOTf, respectively.

The chemoselective cross-coupling of silyl enol ethers and allylic silanes to γ,δ-unsaturated ketones is achieved by the oxovanadium (V)-induced oxidative desilylation of the more readily oxidizable organosilicon compounds.

Benzylic silanes bearing an electron-donating group at the ortho - or para -position underwent the oxovanadium(V)-induced one-electron oxidative desilylation due to low ionization potential, which was applied to the intermolecular regioselective coupling with allylic silanes or silyl enol ether.

The Ca2+ complexes of PQQ-2, 9-dimethyl ester and its iminoquinone derivative have been synthesised and the reactivity towards alcohols examined; the oxidising ability of the quinone is significantly enhanced by binding Ca2+ and NH3, both of which are essential for quinoprotein methanol dehydrogenase activation.

Polyfunctionalized heterocycles have been important key compounds in the fields of functional and biologically active substances. From this point of view, we have developed novel synthetic methods for polyfunctionalized heterocycles according to the following approaches, 1) polar cycloadditions of three-membered heterocycles and azadienes, 2) functionalization of pyridine nucleus leading to condensed pyridine derivatives, 3) molecular design of novel electron transfer catalysts based on chemical simulation of coenzyme PQQ and TTQ, 4) application of heteroatom compounds as heterocyclic building blocks.

Treatment of benzylamine with a catalytic amount of a binuclear copper(II) complex of 7-azaindole 1 under an oxygen atmosphere at room temperature produced benzylidene-benzylamine and benzonitrile in good yields. This reaction is also applicable to other amines and gives the corresponding imines. Interestingly 1-phenylpyrrolidine was oxidized to cyclic dimers, but, in the presence of triethylamine, it was oxidized to the corresponding γ-lactam.

Thermal rearrangement of aryl-substituted N-(silylmethyl)imines to N-silylaziridines with high cis-selectivity was revealed and workup of the products readily led to cis-aziridine derivatives.

Cyclic ketones underwent ring-opening oxygenation on treatment with VO(OEt)Cl2 in alcohol under oxygen to give the corresponding keto ester or diesters depending on the substituent at 2-position. This system was applicable to a catalytic reaction.

Trimethyl ester of coenzyme PQQ (PQQTME) and PdCl2 constitute an effective redox system on treatment with terminal olefin in DMF-H2O, which permits the PdCl2-PQQTME catalyzed Wacker oxidation reaction under oxygen.