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Hydroxyamide-functionalized azolium salt (NHC•HI 4) was evaluated for dual enantioselective control in a Cu-catalyzed asymmetric conjugate addition (ACA) reaction. This investigation was based on our previously reported ACA reaction catalyzed using CuOTf combined with NHC•AgI complex 1. It was revealed that the stereocontrol of the catalytic ACA reaction depended on the order of the addition of the substrates. Additionally, the chiral NHC ligand precursors, substrates, the relationship between the catalyst ee (eecat) and product ee (eepro), and halogen counter anion were completely evaluated. These results suggested that the catalytic performance of the CuOTf/4 system was comparable with that of the CuOTf/1 system. Furthermore, to gain knowledge of the Cu species generated using CuOTf and NHC ligand precursor, the reaction of CuOTf with 1 was investigated. Although obtaining the corresponding NHC•CuX species failed, the corresponding NHC•AuCl complex 11 could be synthesized by allowing 1 to react with AuCl•SMe2.

This study aims to propose a simple procedure for the development of enantioselective hydrosilylation of a ketone using catalytic amounts of [Ir(cod)2]BF4 and chiral azolium salt. Previously, catalytic asymmetric hydrosilylation reactions have used well-defined metal-N-heterocyclic carbene (NHC) complexes. The proposed method offers an important advantage of avoiding preparation of NHC-metal species. Several reaction parameters including the amount of reductant, solvent, catalyst loading and ligand structure were evaluated. In addition, the investigation of the reaction progress as a function of time revealed that an iridium species, which was generated after 5 h of reaction time, catalyzed the stereoselective reduction with almost perfect facial selection of the ketone. An attempt to obtain a catalytic active species from the reaction of [Ir(cod)2]BF4 and chiral azolium salt has been made. The newly obtained iridium species promoted the hydrosilylation of a ketone with high yield and enantioselectivity.

We report three different transformations in the reaction of the hydroxyamide-functionalized azolium chloride 1 with Ag2O. These transformations were controlled by the N-substituent at the azolium ring of 1. Treatment of 1c (R = Me, alkyl) with Ag2O afforded the corresponding monodentate NHC-Ag (NHC represents N-heterocyclic carbene) complex, 6c, in 95% yield. In contrast, the reaction of 1b (R = Ph, aryl) with Ag2O yielded the corresponding 2-hydroxyoxazolidine-substituted azolium hydroxide, 7b, in 90% yield. In this transformation, perhaps the cyclization of the hydroxyamide moiety of 1b to 2-hydroxyoxazolidine occurred under the influence of the hydroxide counter anion. Several aryl-substituted azolium chlorides, 1d-f, were also converted into the corresponding cyclization products, 7d-f. However, the reaction of 1h (R = 2,4,6-Me3C6H2, aryl) with Ag2O afforded the corresponding NHC-Ag complex, 6h, in 93% yield, whereas the reaction of 1i (R = 4-MeOC6H4, aryl) with Ag2O provided a mixture of 6i and 7i in 56% and 32% yields, respectively. Moreover, the reaction of azolium chloride, 1j (R = 2,6-iPr2C6H3, aryl), which has a more sterically hindered substituent at the ortho-position of the aryl side-arm, was investigated. Treatment of 1j with Ag2O gave unexpected urea derivative, 8j, in 99% yield.

Enantioselective reduction of ketones with (EtO) 2 MeSiH catalyzed by an in-situ generated N -heterocyclic carbene (NHC) Ir complex at room temperature has been developed. A series of benzimidazolium salts were synthesized and screened in the asymmetric hydrosilylation reaction. As a result, propiophenone was efficiently reduced by the combined catalytic system of [IrCl(cod)] 2 and NHC–Ag complex derived from N -(1-naphthalenylmethyl)-substituted benzimidazolium salt L12 , affording the corresponding alcohol in 92% yield and with 92% ee. Moreover, the evaluation of an Ir catalyst precursor showed that cationic [Ir(cod) 2 ]BF 4 complex could be used. Furthermore, the introduction of a chiral hydroxyamide side arm into the benzimidazolium salt was critical for the successful design of the NHC ligand.

The asymmetric 1,4-addition of Et2Zn to 2-cyclohexen-1-one using a Cu(I) salt/N-heterocyclic carbene (NHC)–Ag complex catalytic system afforded optically active 3-ethylcyclohexanone. The reversal of enantioselectivity using the same catalytic system was achieved by changing the order of the addition of substrates.

C 2 -symmetric ester-amide functionalized azolium salt was synthesized from readily available α-amino ester such as L -serine methyl ester. The combination of a Cu salt and the chiral azolium salt promoted the asymmetric conjugate addition reaction of enones with dialkylzincs. Thus, treatment of acyclic enone such as chalcone with Et 2 Zn afforded the corresponding 1,4-adduct with up to 85% ee. An excellent ee value of 93% was obtained when 3-nonen-2-one was reacted with Et 2 Zn. The present catalytic system was found to be useful for the 1,4-addition reaction of cyclic enone. For example, the reaction of 2-cyclohepten-1-one with Et 2 Zn produced ( R )-3-ethylcycloheptanone with 80% ee.

A hydroxyamide-functionalized azolium salt as the precursor of a (±)-trans-1,2-cyclohexanediamine-based bis(NHC) ­ligand was designed and synthesized from readily accessible l -leucinol. The combination of a Cu salt with this chiral ligand precursor promoted the asymmetric conjugate addition of Et2Zn to 2-cyclohexen-1-one at room temperature without the need for temperature control to afford the corresponding 1,4-adduct with up to 95% ee.

A series of new N-heterocyclic carbene (NHC)–Ru(II) complexes functionalized with additional hemilabile donor groups, such as a hydroxy-amide group, were successfully synthesized and structurally characterized. Preliminary studies indicated that the complexes acted as precatalysts with moderate activity in the asymmetric transfer hydrogenation at room temperature without temperature control. The investigation of the effect of varying the η 6 -arene ligands showed that these ligands appeared to significantly alter the activity of the complexes as precatalysts. Furthermore, it was revealed that the hydroxy functional group on the NHC ligand side-arm not only induced the stereoselectivity of the reaction but also enhanced the reaction rate.

The versatility of the anionic tethered NHC ligand system for the Pd-catalyzed allylic asymmetric alkylation (AAA) reaction was investigated. A well defined anionic amidate/NHC–Pd(II) complex catalyzed the AAA reaction of 1,3-diphenylprop-3-en-1-yl acetate (5) with NaCH(CO2Me)2. Similarly, the AAA reaction occurred by employing an NHC–Pd(II) complex that was generated in situ. Screening of a wide variety of NHC ligand precursors revealed that the combination of [Pd(allyl)Cl]2 and the azolium salt 9, containing a 3-pentyl group at N(3) position in the NHC ring, efficiently promoted the AAA reaction to afford the corresponding alkylated product 7 with 67% ee. Furthermore, it was found that the Pd/NHC ratio was an important factor; the AAA reaction with a Pd/NHC ratio of 1:1 took place smoothly, whereas utilization of a Pd/NHC ratio of 1:2 resulted in low conversion of the substrates probably by the formation of the catalytically inert bis(NHC)–Pd(II) complex. In fact, an independent experiment showed that the bis(NHC)–Pd(II) complex was formed by treating [Pd(allyl)Cl]2 with two equivalents of NHC–Ag complex. Further investigations on the catalytic AAA reaction revealed significant improvements in both the product yield (99%) and the enantioselectivity (81% ee) when cyclopentyl methyl ether was used as a solvent. A plausible reaction intermediate was discussed.

A series of highly tunable, functionalized azolium compounds have been synthesized from chiral α-amino acid derivatives such as β-amino alcohols or α-amino esters. The combination of a Cu salt and a chiral azolium efficiently facilitated the asymmetric conjugate addition (ACA) reactions of acyclic enones with dialkylzinc under ambient conditions without temperature control. Of the (hydroxy amide)-functionalized azolium ligand precursors, which were derived from β-amino alcohols, an azolium salt containing a tert-butyl group as the stereodirecting group was found to be the best choice of ligand. Ligand screening revealed that the use of an azolium salt containing a sterically bulky alkyl substituent such as N-CHRR′ on the azolium ring led to a marked increase in the enantioselectivity of the ACA reaction. Thus, a new efficient (hydroxy amide)-functionalized azolium ligand precursor such as 26, which was prepared from 1-(diphenylmethyl)benzimidazole and (S)-tert-leucinol, has been developed. The treatment of benzalacetone (30) with Et2Zn in the presence of catalytic amounts of [Cu(OTf)]2(C6H6) and 26 at room temperature gave the corresponding 1,4-adduct 31 with excellent enantioselectivity (92 % ee). On the other hand, the enantioselectivity of the ACA reactions of acyclic enones with dialkylzinc was successfully reversed by the use of (ester amide)-functionalized azolium salts, which were obtained from α-amino esters. Several functionalized azolium ligand precursors from readily available serine esters have been designed and synthesized. Finally, it was found that 30 could react with Et2Zn under the influence of a bis(hexafluoroacetylacetonato)copper(II) salt and C2-symmetric azolium salt 36 to afford ent-31 in almost quantitative yield with 89 % ee. A plausible reaction mechanism for the switching of the stereoselectivity in the ACA reaction by these two functionalized azolium compounds is described.

A new chiral N -heterocyclic carbene (NHC) ligand derived from a natural α-aminoester has been designed and synthesized. The coupling of N -methylbenzimidazole with an α-chloroacetamide derivative, which was prepared from chloroacetyl chloride and ( S )-serine methyl ester, gave the corresponding ester/amide-functionalized azolium compound 20 . The reaction of 2-cyclohexen-1-one ( 17 ) with Et 2 Zn in the presence of catalytic amounts of Cu(OTf) 2 and 20 produced ( R )-3-ethylcyclohexanone ( 18 ) as a major product. In contrast, the enantioselective conjugate addition (ECA) reaction catalyzed by Cu(OTf) 2 under the influence of a hydroxy-amide-functionalized azolium compound 15 , which was derived from ( S )- tert -leucinol, produced ( S )- 18 in preference to ( R )- 18 . A series of azolium salts were synthesized from ( S )-serine esters, and the reaction conditions for the ECA reaction were optimized to produce ( R )- 18 with 69% ee. The best results were obtained in the case of the reaction of 4,4-dimethyl-2-cyclohexen-1-one ( 34 ) with Et 2 Zn catalyzed by Cu(OTf) 2 in combination with azolium compounds. When the reaction of 34 with Et 2 Zn was carried out in the presence of catalytic amounts of Cu(OTf) 2 and 20 , ( S )-3-ethyl-4,4-dimethylcyclohexanone ( 35 ) was obtained with 97% ee, whereas the ECA reaction under the influence of hydroxy-amide-functionalized azolium 15 afforded ( R )- 35 with >99% ee. In this manner, the reversal of enantioselectivity was achieved by controlling the structure of chiral ligands.

A new monodentate iridium(III) complex bearing a readily accessible and tunable chiral hydroxy-amide functionalized N-heterocyclic carbene ligand, Cp∗Ir(NHC)Cl2, has been synthesized and characterized by crystallographic methods. The monodentate Cp∗Ir(NHC)Cl2 complex was found to act as a catalyst precursor for the stereoselective transfer hydrogenation of acetophenone in the presence of KOH even at room temperature. Moderate enantioselectivity was observed in the initial screening of the chiral ligands.

Amide-functionalized N-heterocyclic carbene (NHC) precursors such as azolium compounds have been designed and synthesized. Reaction of PdCl 2 (CH 3 CN) 2 with the NHC–Ag complex derived from the azolium salt gave [(NHC)PdCl 2 ] 2 or (NHC) 2 PdCl 2 , whereas PdCl 2 (PPh 3 ) 2 reacted with the Ag complex to afford a mixed carbene/phosphine complex such as (NHC)(PPh 3 )PdCl 2 together with a cationic [(NHC)(PPh 3 ) 2 PdCl] + Cl − whose structure was characterized by X-ray crystallographic studies. Thus, the library of NHC–Pd complexes with a tethered amide group has been successfully expanded.

A new chiral N-heterocyclic carbene (NHC) ligand was designed. Thus, an efficient synthetic route to C 2 -symmetric bis(hydroxyamide)-functionalized benzimidazolium salts from chiral β-amino alcohols was developed. The combination of Cu(OTf) 2 and the chiral azolium compound efficiently promoted the conjugate addition reaction of cyclic enone with dialkylzinc to give the corresponding adduct in good yield. Among a series of chiral NHC proligands, the functionalized benzimidazolium chloride possessing a tert -butyl group as a stereodirecting group was found to be the best choice of ligand. Under optimized reaction conditions, an excellent enantioselectivity (96% ee) was realized by allowing 2-cyclohepten-1-one to react with Bu 2 Zn at room temperature.

A simple and efficient one-pot procedure for the synthesis of α-diketones from aldehydes via benzoin condensation under the influence of a catalytic amount of azolium salt combined with DBU has been developed. Thus, aldehyde was allowed to react with the azolium salt/DBU catalytic system at room temperature, and then the reaction mixture was heated to 70 °C under air atmosphere to afford the corresponding 1,2-diketone in good yield. This would be an efficient alternative method of synthesizing α-diketones from aldehydes under metal-free conditions.

The synthesis of a series of azolium salts such as azolium iodides and chlorides having both N-anionic functional group and N-alkyl group have been developed. Reaction of azolium iodides or chlorides with Ag2O gave the corresponding NHC–Ag complexes. It was found that the resulting NHC–Ag complexes derived from azolium iodides or chlorides differ in their physical properties. The azolium chlorides as well as azolium iodides were successfully converted into the NHC–Ag complexes, which subsequently reacted with PdCl2(CH3CN)2 to give the anionic amidate/NHC–Pd complexes. Thus, a variety of the NHC–Pd complexes could be obtained from benzimidazolium and imidazolium salts.

While developing novel catalysts for carbon-carbon or carbon-heteroatom coupling (N, O, or F), we were able to introduce tridentate NHC-amidate-alkoxide palladium(II) complexes. In aqueous solution, these NHC-Pd(II) complexes showed high ability for C-H activation of various hydrocarbons (cyclohexane, cyclopentane, dimethyl ether, THF, acetone, and toluene) under mild conditions.

Direct conversion of benzene to phenol was achieved by allowing it to react with a mixed gas of air and CO in the presence of HPMoV and a very small amount of 5%Pd/C in aqueous acetic acid at 150 °C for 2 h. The TON of HPMoV for the formation of phenol goes up to over 1300. The active species of the present reaction is thought to be V4+ generated from HPMoV catalyst by the reduction with CO. The role of the Pd species seems to promote the generation of V4+ from HPMoV. This method is expected to provide a direct route to phenol from benzene.

Carboxylation of benzenes with CO was successfully achieved by a combined catalytic system of Pd(OAc)2 with H5PMo10V2O40·nH2O (HPMo10V2) under the influence of O2 to form the corresponding benzoic acids in relatively high selectivity and moderate yields. The regioselectivity in the carboxylation of alkylbenzenes with CO was dominated by the steric factor rather than the electronic effect of substituents. However, the carboxylation of benzoic acid proceeded with high ortho-selectivity to give phthalic acid in preference to terephthalic acid, which shows coordination of Pd species to the carboxyl group of benzoic acid.

New strategies for lactams synthesis from cycloalkanes without formation of sulfates have been proposed. The synthesis of lactams from cycloalkanes through a one-pot reaction was successfully performed using N-hydroxyphthalimide (NHPI) as a key catalyst. The strategy involves nitrososation of cycloalkanes with tert-butyl nitrite under the influence of NHPI followed by isomerization to oximes and then the Beckmann rearrangement to lactams. For example, e-caprolactam and laurolactam were prepared from cyclohexane and cyclododecane in 74% and 78% yields, respectively, in one-pot. An alternative approach for sulfate-free lactam synthesis includes the nitration of cyclohexane with NO2 to nitrocyclohexane in the presence of NHPI under mild conditions followed by the hydrogenation to cyclohexanone oxime. The Beckmann rearrangement to .e-caprolactam was found to be achieved in quantitative yields by a very small amount of cyanuric chloride in a mixed solvent of trifluoroacetic acid and toluene.

A new synthetic method of substituted furoates from acrylates and aldehydes was developed by Pd(OAc)2 combined with molybdovanadophosphoric acid and Lewis acid under atmospheric dioxygen. The reaction was found to proceed through the palladium-catalyzed acetalization of acrylates with methanol followed by the reaction of the resulting acetals with aldehydes.

A new type of carbonylation of styrenes was achieved under a 1:1 mixture of CO (0.5 atm) and O2 (0.5 atm) in the presence of Pd(OAc)2 combined with H5PMo10V2O40·nH2O to give 4-methyl-2-phenylnaphth...

Concomitant introduction of COOH and OH groups to biphenyl was achieved by allowing biphenyl to react with CO and O2 using the Pd/molybdovanadophosphoric acid catalytic system. For instance, biphenyl reacted under a mixed gas of CO (0.5 atm) and O2 (0.5 atm) in the presence of catalytic amounts of Pd(OAc)2 and H5PMo10V2O40·26H2O in acetic acid to give the corresponding hydroxybiphenylcarboxylic acids. The reaction was found to proceed through the formation of biphenylcarboxylic acid followed by hydroxylation of the resulting carboxylic acid.

Innovative carbon radical generation from hydrocarbons through a catalytic process under mild conditions has been achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst. This method can be successfully applied to a wide variety of functionalizations of hydrocarbons. Thus, alkanes are converted into alcohols, ketones, and carboxylic acids, through alkyl radicals generated by the action of NHPI. Cyclohexane was directly converted into adipic acid with O2 by NHPI combined with Mn(OAc)2. p-Xylene was oxidized to terephthalic acid in 95% yield by using an NHPI analogue as a catalyst. Alkenes could be epoxidized with H2O2 generated in situ from benzhydrol and O2 under the influence of NHPI.

The oxidation of trimethylbenzenes was examined with air or O 2 using N , N ′, N ″-trihydroxyisocyanuric acid (THICA) as a key catalyst. Thus, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzenes under air (20 atm) in the presence of THICA (5 mol %), Co(OAc) 2 (0.5 mol %), Mn(OAc) 2 , and ZrO(OAc) 2 at 150 °C were oxidized to the corresponding benzenetricarboxylic acids in good yields (81–97%). In the aerobic oxidation of 1,2,4-trimethylbenzene by the THICA/Co(II)/Mn(II) system, remarkable acceleration was observed by adding a very small amount of ZrO(OAc) 2 to the reaction system to form 1,2,4-benzenetricarboxylic acid in excellent yield (97%). In contrast, no considerable addition effect was observed in the oxidation of 1,3,5-trimethylbenzene. This aerobic oxidation by the present catalytic system provides an economical and environmentally benign direct method to benzenetricarboxylic acids, which are very important polymer materials.

The addition of water and alcohols to non-activated terminal alkynes was found to be promoted by an iridium complex combined with Lewis acid and phosphite. Thus, terminal alkynes reacted with water or alcohols to give ketones or ketals, respectively, in good to excellent yields. α,ω-Diyne like 1,7-octadiyne was converted into 1-(2-methyl-cyclopent-1-enyl)ethanone through the intramoleculer aldol condensation of the resulting 2,7-octanedione induced by Lewis acid.

Aerobic oxidation of hydroaromatic compounds and diarylalkanes by N-hydroxyphthalimide (NHPI) under mild conditions afforded the corresponding hydroperoxides in high selectivity. Treatment of the resulting hydroperoxides with sulfuric acid followed by neutralization by a base resulted in phenol and aromatic aldehydes in high selectivity. This method provides a convenient synthetic route to aldehydes involving an aromatic moiety.

The first systematic study on the aerobic oxidation of 1,3,5-triisopropylbenzene was examined by the use of N-hydroxyphthalimide (NHPI) as a key catalyst. It was found that 1,3,5-triisopropylbenzene was efficiently oxidized with O2 in the presence of a catalytic amount of NHPI and azobisisobutyronitrile (AIBN) at 75 °C. Upon treatment of the resulting products with sulfuric acid followed by acetic anhydride led to 5-acetoxy-1,3-diisopropylbenzene and 3,5-diacetoxy-1-isopropylbenzene as major products and a small amount of 1,3,5-triacetoxybenzene. When t-butylperoxypivalate (BPP) was employed as a radical initiator, the oxidation could be achieved in good yield even at 50 °C. This oxidation provides a facile method for preparing phenol derivatives bearing an isopropyl moiety, which can be used as pharmaceutical starting materials.

A direct synthetic method of cresols from toluene by hydroxylation with air using CO as a reducing agent was developed. The reaction of toluene with air (15 atm) and CO (5 atm) in the presence of catalytic amounts of H4PMo11VO40·31H2O and Pd/C in aqueous acetic acid at 120 °C for 2 h afforded a mixture of o-, m-, and p-cresols in 9.9% yield at 83% selectivity. Cresols were obtained in 19% yield by recharging air and CO under these conditions. A variety of substituted benzenes were hydroxylated by this method to give the corresponding phenol derivatives in higher selectivity.

Synthesis of phenol and cyclohexanone in one pot was examined by means of the NHPI-catalyzed aerobic oxidation of cyclohexylbenzene. The aerobic oxidation of cyclohexylbenzene catalyzed by NHPI followed by treatment with sulfuric acid afforded phenol and cyclohexanone in good selectivities. Thus, the reaction of cyclohexylbenzene under atmospheric dioxygen (1 atm) by NHPI at 100 °C for 3 h followed by treatment with 0.3 M sulfuric acid at room temperature for 2 h resulted in phenol and cyclohexanone in 96 and 91% selectivity, respectively, at 25% conversion. This method was successfully extended to the one-pot synthesis of 4-hydroxyacetophenone and cyclohexanone.

Naphthalenediols were successfully synthesized in a one-pot reaction through the oxidation of diisopropylnaphthalenes with air catalyzed by N-hydroxyphthalimide (NHPI) combined with α,α′-azobisisobutyronitrile (AIBN) followed by decomposition with sulfuric acid. Thus, the oxidation of 2,6-diisopropylnaphthalene with air (20 atm) in the presence of AIBN (3 mol %) and NHPI (10 mol %) in CH3CN at 75 °C for 21 h followed by treatment with 0.3 M H2SO4 gave 2,6-naphthalenediol in 92% yield.

Radical addition of aldehydes and masked aldehydes like 1,3-dioxolanes to electron-deficient alkenes was achieved by the use of catalytic amounts of BPO and N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst under mild conditions. Three-component radical coupling of 1,3-dioxolanes, maleates, and alkenes was performed in the presence of BPO and NHPI under similar conditions.

Nitrotoluenes are efficiently oxidized with air to the corresponding nitrobenzoic acids by the use of N -acetoxyphthalimide (NAPI) as a key catalyst. Thus, p - and m -nitrotoluenes under 10 atm of air in the presence of NAPI combined with Co(OAc) 2 (0.5 mol%) and Mn(OAc) 2 (0.05 mol%) at 130°C afforded p - and m -nitrobenzoic acids in 81 and 92% yields, respectively. o -Nitrotoluene was oxidized to o -nitrobenzoic acid in 51% yield by the aid of NO 2 .

Selective Wacker-type oxidation of long-chain terminal alkenes to methylketones was successfully achieved by using Pd(OAc) 2 /molybdovanadophosphate (NPMoV)/O 2 system. The selectivity of the reaction increased by slow addition of the alkenes to the catalytic solution. The oxidation of α,ω-dienes was also examined, and the selectivity of the oxidation was found to depend on the chain length of the dienes used.

Oxidative carbomethoxylation of cyclopentene (1) under carbon monoxide and air by the use of a catalytic amount of Pd(OAc)(2) and molybdovanadophosphate (NPMoV) led to dimethyl cis-1,2-cyclopentanedicarboxylate (2) and dimethyl cis-1,3-cyclopentanedicarboxylate (3) in good yields. Total yields of 2 and 3 were found to be improved by adding a small amount of NH(4)Cl. Several alkenes were similarly converted into the corresponding dimethyl dicarboxylates. The role of Cl(-) in the present catalytic system is suggested.

The reaction of various ethers with alkenes bearing an electron-withdrawing substituent in the presence of N -hydroxyphthalimide combined with Co(OAc) 2 under dioxygen produced the corresponding adducts in which oxygen is incorporated to alkenes in good yields. Oxcetane, furan and pyrane smoothly added to ethyl fumarate even at room temperature to give coupling products in high yields. An acyclic ether like dibutyl ether also added to fumarate under mild conditions to give a hydroxylated adduct in satisfactory selectivity.

An efficient approach to phenols and aldehydes through the formation of hydroperoxides from alkylbenzenes was successfully achieved by aerobic oxidation using N-hydroxyphthalimide (NHPI) as a catalyst. The oxidation of various alkylbenzenes with dioxygen by NHPI followed by treatment with a Lewis acid or triphenylphosphine led to phenols or aldehydes, respectively, in good yields. For example, the aerobic oxidation of cumene in the presence of a catalytic amount of NHPI at 75 °C and subsequent treatment with H2SO4 gave phenol in 77% yield. 1,4-Dihydroxybenzene (61%) and 4-isopropylphenol (33%) were obtained from 1,4-diisopropylbenzene. On the other hand, dibenzyl ether was converted into phenol or benzaldehyde upon treatment of the resulting hydroperoxide with InCl3 or PPh3, respectively.

A novel catalytic method for the radical addition of alkanes and molecular oxygen to electron-deficient alkenes was achieved by the use of N-hydroxyphthalimide (NHPI) combined with a Co species as the catalyst. This reaction is referred to as oxyalkylation of alkenes with alkanes and O(2). For instance, the reaction of 1,3-dimethyladamantane with methyl acrylate under molecular oxygen in the presence of catalytic amounts of NHPI and Co(acac)(3) at 70 degrees C for 16 h gave oxyalkylated products in 91% yield. Other alkenes such as fumarate and acrylonitrile also serve as good acceptors of alkyl radicals and O(2) to afford the corresponding adducts in high yields. The generality of the present reaction was examined between various alkanes and alkenes under dioxygen. The behavior of Co ions during the reaction course was discussed. The present reaction involves (i) an alkyl radical generation via hydrogen abstraction of alkane by phthalimide N-oxyl generated in situ from NHPI and O(2) assisted by Co(II), (ii) the addition of the resulting alkyl radical to an electron-deficient alkene to form an adduct radical, (iii) trapping of the adduct radical by O(2) yielding a hydroperoxide, and (iv) the decomposition of the hydroperoxide by Co ions to form an adduct in which a hydroxy or a carbonyl function is incorporated.

A new methodology for the production of terephthalic acid (3) by the aerobic oxidation of p-xylene (1) using a combined catalytic system of N-hydroxyphthalimide (NHPI)/Co(OAc) 2/Mn(OAc) 2was developed. The oxidation of 1 under a dioxygen atmosphere in the presence of a catalytic amount of NHPI/NHPI(OAc) 2/Mn(OAc) 2at 100 °C for 14 h afforded terephthalic acid in 82% yield. Removal of Mn(OAc) 2 from the catalytic system resulted in considerable reduction in the yield of 3. When the oxidation of 1 was carried out under a pressure of air (30 atm) at 150 °C, the reaction was completed within 3 h to give 3 in 84% yield. The oxidation of p-toluic acid (2), which can be prepared by the oxidation of 1 using the NHPI/NHPI(OAc) 2 system at room temperature, by the NHPI/NHPI(OAc) 2/Mn(OAc) 2system under pressure of air (30 atm) at 150 °C gave 3 in 95% yield. N-Acetoxyphthalimide (NAPI) was found to require a lower catalyst loading than NHPI, but oxidation with NAPI was slower. Thus, the oxidation of 1 catalyzed by NAPI (5 mol %)/Co(OAc) 2 (0.5 mol %)/Mn(OAc) 2 (0.5 mol %) under a dioxygen atmosphere (1 atm) in acetic acid at 100 °C gave 3 in 80% yield.

Innovative carbon radical generation from hydrocarbons through a catalytic process under mild conditions has been achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst. This method can be successfully applied to a wide variety of functionalizations of hydrocarbons. Thus, alkanes are converted into alcohols, ketones, carboxylic acids, nitro alkanes and alkyl sulfonic acids through alkyl radicals generated by the action of NHPI. Hydroxysilylation was first performed by the addition of hydrosilanes and oxygen to alkenes bearing electron-withdrawing substituents. A new approach to oxyalkylation based on the concomitant addition of carbon radicals derived from alkanes or alcohols and molecular oxygen to alkenes or alkynes has been described.

Treatment of homoallylic alcohols with NaIO 4 /NaHSO 3 reagent in aqueous t -BuOH under mild conditions produced tetrahydrofuran derivatives together with iodohydrins in a stereospecific manner. The reaction pathways of the formation of tetrahydrofurans from trans - and cis -homoallylic alcohols were found to be different. The present method provides a new approach to various alkylated tetrahydrofuran derivatives.

Selective aerobic oxidation of methylpyridines to pyridinecarboxylic acids was successfully achieved by the use of a radical catalyst, N-hydroxyphthalimide (NHPI), in the presence of Co(II) and/or Mn(II) salts. The oxidation of 3-methylpyridine by NHPI combined with Co(OAc)2 under O2 (1 atm) in AcOH at 100 °C gave 3-pyridinecarboxylic acid (76%). The reaction was found to be enhanced by addition of a small amount of Mn(OAc)2 to the catalytic system. The reaction with 20 atm of air, catalyzed by NHPI−Co(OAc)2−Mn(OAc)2 at 150 °C for 1 h, gave 3-pyridinecarboxylic acid (85%). 4-Methylpyridine was much less easily oxidized than 3-methylpyridine. The co-oxidation of 3-methylpyridine and 4-methylpyridine by NHPI−Co(OAc)2−Mn(OAc)2 at 150 °C for 5 h gave results that were better than those obtained from individual oxidations, forming 3-pyridinecarboxylic acid (93%) and 4-pyridinecarboxylic acid (70%). The NHPI-catalyzed oxidation of methylpyridines would provide an attractive direct method which has long been des...

The reaction of oxime esters with cyanotrimethylsilane (Me(3)SiCN) under the influence of a catalytic amount of lanthanide compounds produced alpha-trimethylsilyloxydinitrile derivatives in excellent yields accompanied with the formation of trimethylsilyl oxime ethers. Among the lanthanoid catalysts examined, La(O(i)()Pr)(3) was found to be the best catalyst. The reaction seems to proceed through the formation of acyl cyanides as intermediates, followed by the addition of Me(3)SiCN to them. Additionally, the reaction of acetic anhydride with Me(3)SiCN catalyzed by La(O(i)()Pr)(3) gave 1-trimethylsilyloxyethane dinitrile. Thus, various alpha-trimethylsilyloxydinitriles were synthesized in good yields by allowing oxime esters or acid anhydrides to react with Me(3)SiCN in the presence of a catalytic amount of La(O(i)()Pr)(3).

A new method for the synthesis of 1,3-oxazolidine derivatives has been developed. Thus, a variety of 1,3-oxazolidines was prepared by the reaction of imines with epoxides in the presence of a catalytic amount of a samarium compound such as SmI 2 , SmI 3 , or Cp* 2 Sm(thf) 2 .

Meerwein–Ponndorf–Verley-type reductive acetylation of carbonyl compounds to acetates was successfully carried out in the presence of isopropenyl acetate under the influence of a catalytic amount of Ln(O i Pr) 3 at room temperature. Various carbonyl compounds were converted into the corresponding acetates in fair to good yields.

The utilization of lanthanide metal salts and organolanthanide compounds in organic synthesis has been attracted considerable attention, however, there have been a limited number of studies on the synthetic reactions using divalent samarium compounds such as SmI2 and Cp*2Sm (thf) 2 as catalysts or catalyst precursors. We report here several synthetic reactions by the use of samarium complexes (II), namely SmI2 and Cp*2Sm (thf) 2, as catalysts : (i) coupling reaction of vinyl esters with aldehydes, (ii) acylation of alcohols and amines with vinyl esters, (iii) acylation of tertiary alcohols with vinyl esters in the presence of a catalytic amount of oxime ester, (iv) synthesis of 1, 3-diol monoesters by the trimerization of aldehydes, (v) aldol type condensation of imines, and (vi) one-pot synthesis of pyrroles by the reaction of amines, aldehydes, and nitroalkanes.

Wacker-type oxidation of cyclopentene to cyclopentanone under dioxygen atmosphere was successfully achieved by the use of Pd(OAc) 2 and molybdovanadophosphate supported on activated carbon, [Pd(OAc) 2 –NPMoV/C], catalyst. Thus, the reaction of cyclopentene under O 2 (1 atm) in aqueous acetonitrile acidified by CH 3 SO 3 H in the presence of [Pd(OAc) 2 –NPMoV/C] at 50°C produced cyclopentanone in 85% yield along with a small amount of cyclopentenone (1%).

Various types of substituted alkylpyrroles were synthesized in regioselective manner by the cyclization of nitroalkenes with imines catalyzed by Sm(O i -Pr) 3 under mild conditions. Tetrahydroindole derivative was also synthesized in fair yield by the use of cyclic nitroalkene and imine as starting material. This method provides a novel alternative route for the regioselective synthesis of substituted alkylpyrrole derivatives.