Oxidation Of 1a Research Articles

ChemInform Abstract: Photochemical and ESR Spectral Evidence for a Stereoselective Rearrangement of Radical Cations Derived from Azoalkanes and Bicyclopentanes.

Studies of photosynthesized electron transfer (PET) reactions of anti/syn-5-methylbicyclo[2.1.0]pentane (1a,b) and syn/anti-7-methyl-2-3-diazabicyclo[2.2.1]hept-2-ene (2a,b) have revealed a remarkable stereochemical memory effect. Thus, 1a and 2a furnished only 1-methylcyclopentene (3b). The pathway responsible for the stereoselective olefin formation can be assigned to a radical cation rearrangement. This was established on the basis of direct ESR evidence showing that the 1,3-diyl radical cations 1a,b{sup .+} detected initially at 80-90 K following the radiolytic oxidation of 1a,b in CF{sub 3}CCI{sub 3} rearranged stereoselectively into the olefin radical cations 3a,b{sup .+} at 105 K. The ESR results further establish that, in the puckered conformations of 1a,b{sup .+}, the psuedo-axial substituent on the methylene bridge is almost perfect coplanar alignment with the radical cation 2p orbital lobes, thus facilitating is stereoselective migration. Also, in agreement with (PET) results, matrix ESR studies demonstrated that, on radiolytic oxidation of the azoalkanes 2a,b, the olefin radical cation 3a,b{sub .+} were formed with high selectivity, although no precursor radical cations were detected in this case. 29 refs., 5 figs., 2 tabs.

ChemInform Abstract: Carbonyl O-Oxides and Dioxiranes: The Influence of Substituents on Spectroscopic Properties.

Triplet 4-oxocyclohexadienylidenes 6, matrix-isolated in Ar/ 2% O2 at 10 K, react with triplet O2 on annealing the matrix. Primary reaction products are quinone oxides 4, which have been characterized by IR and UV/Vis spectrometry. They are very photolabile; long-wavelength irradiation converts them into spiro-dioxiranes 5, which in turn yield lactones 10 upon irradiation with visible light. Experimental data have been obtained for quinone oxides 4a–g; additionally, ground-state properties and UV/Vis absorptions of quinone oxides 4a,b and 4e–1 have been calculated by the MINDO-3/UHF and CNDO/S methods. Since the theoretical and experimental maxima of the π π* transitions are in good agreement, we conclude that our semiempirical calculations give an adequate picture of quinone oxides 4 which may best be described as dipolar diradicals.

Synthesis, structural characterisation and anti-proliferative activity of NHC gold amino acid and peptide conjugates

We report the synthesis of new NHC gold(I) and NHC gold(III) halide, amino acid and dipeptide complexes. Transmetallation of the N-phenylalanine-substituted NHC silver complex 3 with Me2SAuCl yields the phenylalanine-NHC gold(I) conjugate 4a. Halide exchange with LiBr and oxidation of 4a with Br2 in CH2Cl2 yields the phenylalanine-NHC Au(I) and Au(III) bromides 4b and 4c, respectively. Reaction of N-Boc protected cysteine methyl ester (Boc-Cys-OMe) or the dipeptide N-Boc-Leu-Cys-OMe with the NHC gold chloride 6a yields the (NHC)Au-S complexed amino acid and dipeptide derivatives 8 and 9. The NHC gold(III) complexes 4c and 6c were characterised by single crystal X-ray analysis. All of the tested gold carbene complexes showed significant anti-tumor activity on the HeLa, HepG2 and HT-29 cancer cell lines. The best compounds show activity comparable to the well-known anti-cancer drug cisplatin. There seems to be no clear cut structure-activity relationship in the compounds tested, nor did we observe a dependence on the metal oxidation state or the different halide substituents. Given the ease of preparation, stability and high activity of the compounds described herein, it may be possible to design tumor-specific anti-cancer agents based on NHC gold amino acid conjugates in the future.

Synthesis and Antiviral Activities of Pyrazole Derivatives Containing an Oxime Moiety

Target compounds 4a- n were obtained by the reaction of 1-substituted phenyl-3-methyl-5-substituted phenylthio-4-pyrazolaldoximes (3) with chloromethylated heterocyclic compounds (ClCH 2-R 3) under reflux conditions in ethanol. Subsequently, the oxidation of 4a- e with KMnO 4 in HOAc at room temperature afforded eight new compounds, 5a- h. The synthesized compounds were characterized by physical constants, and the structures of the title compounds were confirmed by IR, (1)H NMR, (13)C NMR, and elemental analysis. The bioassay revealed that the compounds possessed antiviral activities. It was found that title compounds 4a and 4g had the same inactivation effects against TMV (EC 50 = 58.7 and 65.3 microg/mL) as the commercial product Ningnanmycin (EC 50 = 52.7 microg/mL). To the best of our knowledge, this is the first report on the antiviral activity of pyrazole derivatives containing an oxime moiety.

Oxidation of diethyl N‐sulfinylphos‐phoramidates

AbstractIt is reported that the diethyl N‐sulfinylphosphoramidate (1a) is oxidized with iodoso‐ and/or iodoxybenzene as well as with organic peroxides, to give diethyl N‐sulfonylphosphoramidate (7a). The latter was generated in situ at low temperature and trapped with dialkyl phosphoramidates, affording the N,N′ bis(dialkyl phosphor)sulfamides 3a–c. The oxidation of 1a with cumene peroxide in the presence of 2,2‐dimethyl‐propan‐1‐ol (9) produced the diethylphosphor‐N‐[2,2‐dimethylpropyl]sulfamate (10a). © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:530–536, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20474

Synthesis and X‐ray Structures of the Polycyclic Dimers {[PhB(μ‐NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ‐NtBu)2AsN(tBu)Li]2

AbstractThe metathesis of [PhB(μ‐NtBu)2]AsCl and tBuN(H)Li in 1:1 molar ratio in diethyl ether produced the amido derivative [PhB(μ‐NtBu)2AsN(tBu)H] (1) in good yield. The lithiation of 1 with one equivalent of nBuLi afforded the lithium salt [PhB(μ‐NtBu)2AsN(tBu)Li] (2a). Both 1 and 2a were characterized by multinuclear NMR spectroscopy. The crystal structure of 2a is comprised of a U‐shaped, centrosymmetric dimer in which the monomeric [PhB(μ‐NtBu)2AsN(tBu)]−Li+ units are linked by Li‐N interactions to give a six‐rung ladder. Oxidation of 2a with one‐half equivalent of I2 in diethyl ether resulted in hydrogen abstraction from the solvent to give the dimeric lithium iodide adduct {[PhB(μ‐NtBu)2AsN(tBu)H]LiI}2 (1·LiI) with a central Li2I2 ring.

Singlet Diradical Complexes of Chromium, Molybdenum, and Tungsten with Azo Anion Radical Ligands from M(CO)6Precursors

The homoleptic diamagnetic complexes M(mer-L)(2), M = Cr, Mo,W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO)(6) with the tridentate ligands 2-[(2-N-arylamino)phenylazo]pyridine (HL = NH(4)C(5)N=NC(6)H(4)N(H)C(6)H(4)(H) (HL(a)) or NH(4)C(5)N=NC(6)H(4)N(H)C(6)H(4)(CH(3)) (HL(b))) in refluxing n-octane. In the case of M = Mo, the dinuclear compounds [Mo(L)(pap)](2)(mu-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction analysis for Cr(L(b))(2) (1b), Mo(L(a))(2) (2a), and W(L(a))(2) (4a) reveals considerably distorted-octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyl-N and anilido nitrogen atoms. Whereas the N(azo)-M-N(azo) angle is larger than 170 degrees, the other two trans angles are smaller, at about 155 degrees (M = Cr, 1b) or 146 degrees (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by more than 0.08 A than those to the anilido or azo nitrogen atoms, reflecting negative charge on the latter. The N-N bond distances vary between 1.339(2) A for 1b and 1.373(3) A for 4a, clearly indicating the azo radical anion oxidation state. Considering the additional negative charge on anilido-N, the mononuclear complexes are thus formulated as M(IV)(L*(2-))(2). The diamagnetism of the complexes as shown by magnetic susceptibility and (1)H NMR experiments is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The experimental structures are well reproduced by density functional theory calculations, which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) A for L(a) and 1.340(9) A for pap is also formulated as an azo anion radical-containing molybdenum(IV) species, i.e., [Mo(IV)(L*(2-))(pap*-)](2)(mu-O). All compounds can be reversibly reduced; the Cr complexes 1a,b are also reversibly oxidized in two steps. Electron paramagnetic resonance spectroscopy indicates metal-centered spin for 1a+ and 1a- and g approximately 2 signals for 2a-, 3a+, 3a-, and 4a-. Spectroelectrochemistry in the UV-vis-NIR region showed small changes for the reduction of 2a, 3a, and 4a but extensive spectral changes for the reduction and oxidation of 1a.

In vivo transformations of dihydro- epi-deoxyarteannuin B in Artemisia annua plants

[15- 13C 2H 3]-dihydro- epi-deoxyarteannuin B ( 4a) has been fed to intact Artemisia annua plants via the root and three labeled metabolites ( 17a– 19a) have been identified by 1D- and 2D-NMR spectroscopies. The in vivo transformations of 4a in A. annua are proposed to involve enzymatically-mediated processes in addition to possible spontaneous autoxidation. In the hypothetical spontaneous autoxidation pathway, the tri-substituted double bond in 4a appears to have undergone ‘ene-type’ reaction with oxygen to form an allylic hydroperoxide, which subsequently rearranges to the allylic hydroxyl group in the metabolite 3α-hydroxy-dihydro- epi-deoxyarteannuin B ( 17a). In the enzymatically-mediated pathways, compound 17a has then been converted to its acetyl derivative, 3α-acetoxy-dihydro- epi-deoxyarteannuin B ( 18a), while oxidation of 4a at the ‘unactivated’ 9-position has yielded 9β-hydroxy-dihydro- epi-deoxyarteannuin B ( 19a). Although all of the natural products artemisinin ( 1), arteannuin K ( 7), arteannuin L ( 8), and arteannuin M ( 9) have been suggested previously as hypothetical metabolites from dihydro- epi-deoxyarteannuin B in A. annua, none were isolated in labeled form in this study. It is argued that the nature of the transformations undergone by compound 4a are more consistent with a degradative metabolism, designed to eliminate this compound from the plant, rather than with a role as a late precursor in the biosynthesis of artemisinin or other natural products from A. annua.

Synthesis of 3-Benzyl- or 3-Benzoyl-7,8-dihydro-6H-chromene Derivatives Starting from Baylis-Hillman Adducts

acetate 1 and cyclohexane-1,3-dione (2a) in the presence of K2CO3 in DMF gave 3a in 68% yield. Conversion of 3a into the corresponding lactone derivative 4a was conducted by refluxing 3a in p-xylene to give 4a in 59% yield. The exodouble bond of 4a could be isomerized in its endo-position by treatment with DMAP (4,4-dimethylaminopyridine) in refluxing p-xylene to give 5a in 89% yield. As easily expected, the reaction of 3a in the presence of DMAP in refluxing p-xylene gave 5a in 75% yield directly. In addition, compound 5a was synthesized directly from the reaction of 1 and 2a in 78% yield without separation of the intermediate 3a as also shown in Scheme 1. As a next trial, we examined the allylic oxidation of 4a and 5a, and we found that the reaction of 4a and PCC (pyridinium chlorochlomate) produced the 3-benzoyl derivative 6a in 63% yield. 11 However, the oxidation of 5a with PCC showed no reaction. Like this we found efficient syn

Synthesis and derivatization of angular 3-chloro-3-chlorosulfenyl naphtho[1,2-b]pyran(4H)-4-ones with evaluation of antiviral activity

Angular 2,3-dihydronaphtho[1,2-b]pyran(4H)-4-ones 1a,b react with an excess of thionyl chloride to give the α-chlorosulfenyl chlorides 2a,b, which are reduced by iodide ion to give the corresponding 1,3,4-oxadithiino derivatives 3a,b. However, the aducts 4a,b and 5a,b were obtained by reduced 2a,b with iodide ion in the presence of 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene, respectively. Direct oxidation of 2a,b afford 3,3-dichloronaphthopyran-4-ones 6a,b, whilst conversion to the sulfenamides 7a,b prior to oxidation provides 3-chloronaphthopyranones 8a,b. While α-chloro β-oxo sulfenyl chlorides 2a,b undergo straight forward substitution with 1-methylpiperazine and with potassium cyanide to give 9a,b and 10a,b, respectively. Some of the prepared products were selected and tested for their antiviral activity against herpes simplex virus type-1 (HSV-1). Plaque reduction infectivity assay was used to determine virus count reduction as a result of treatment with test compounds. Compound 5a showed moderate effect against HSV-1.

‘Pincer’ dicarbene complexes of some early transition metals and uranium

The complexes [(C-N-C)MX(n)(thf)(m)] with the 'pincer' 2,6-bis(imidazolylidene)pyridine, (C-N-C) = 2,6-bis(arylimidazol-2-ylidene)pyridine, aryl = 2,6-Pr(i)2C6H3, M = V, X = Cl, n = 2, m = 1 1a; M = Cr, X = Cl, n = 2, m = 0, 2a, X = Br, 2b; M = Mn, X = Br, n = 2, m = 0, 3; M = Nb, X = Cl, n = 3, m = 0, 4; and M = U, X = Cl, n = 4, m = 0, 5, were synthesised by (a) substitution of labile tmed (1a), thf (2a, 3, 5) or dme (4) by free (C-N-C) or by (b) reaction of the bisimidazolium salt (CH-N-CH)Br2 with {Cr[N(SiMe3)2]2(thf)2} followed by amine elimination (2b). Attempted alkylation of 1a, 2, 3a and 4 with Grignard or alkyl lithiums gave intractable mixtures, and in one case [reaction of 1a with (mesityl)MgBr] resulted in exchange of Cl by Br (1b). Oxidation of 1a or [(C-N-C)VCl3] with 4-methylmorpholine N-oxide afforded the trans-V(C-N-C)(=O)Cl2, 6, which by reaction with AgBF4 in MeCN gave trans-[V(C-N-C)(=O)(MeCN)2][BF4]2, 7. Reaction of 1a with p-tolyl azide gave trans-V(C-N-C)(=N-p-tolyl)Cl2 8. The complex trans-Ti(C-N-C)(=NBu(t))Cl2, 9, was prepared by substitution of the pyridine ligands in Ti(NBu(t))Cl2(py)3 by C-N-C.

Ruthenium‐Catalyzed Oxidation of Secondary Alcohols Assisted by a Simple Alkene.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Highly Stereoselective Preparation of CF3‐Substituted 1‐Aryl‐1,2‐diphenylethenes: Application to the Synthesis of Panomifene.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Indeno[1,2‐b]quinolin‐10‐ones via Pd/C‐Assisted Dehydrogenation of 4b,5,10a,11‐Tetrahydroindeno[1,2‐b]quinolin‐10‐ones.

Recently, we have reported the synthesis of 4b,5,10a,11tetrahydroindeno[1,2-b]quinolin-10-ones starting from the acetates of Baylis-Hillman adducts as in Scheme 1. Indenoquinoline derivatives showed a wide range of biological activities such as 5-HT-receptor binding activity, antiinflammatory activity, and also act as antitumor agents, inhibitor for steroid reductase, acetylcholinesterase inhibitors, and antimalarials. These compounds could be synthesized via the aza-Bergman cyclization or via the radical cyclization of isonitrile derivatives. In these contexts, development of a facile synthetic method of indeno[1,2-b]quinoline derivatives would be very important. Thus, we examined the possibility for the synthesis of a variety of indenoquinolines from 4b,5,10a,11-tetrahydroindeno[1,2-b]quinolin-10-one (1a) as shown in Scheme 2. Oxidation of 1a with iodine in methanol would produce 10methoxy-11H-indeno[1,2-b]quinoline. Treatment of 1a with POCl3 followed by dehydrogenation would generate 10chloro-11H-indeno[1,2-b]quinoline. Dehydrogenation of 1a with Pd/C or with related oxidant might produce indeno[1,2b]quinolin-10-one (Scheme 2). Treatment of 1a with POCl3 showed the formation of intractable mixtures, unfortunately. Oxidation of 1a with FeCl3 in methanol (reflux, 3 days) produced low yield of indeno[1,2-b]quinolin-10-one (2a, 21%). The use of 2.5 equivalents of DDQ (benzene, reflux, 10 h) for the oxidation of 1a showed moderate yield of 2a (52%). After many trials, we found that dehydrogenation conditions using Pd/C in refluxing decaline generate 2a in good yield (83%). As shown in Table 1, we prepared some indeno[1,2-b]quinolines 2b-e similarly by using Pd/C. It is noteworthy that dechlorination occurred simultaneously for the chlorinesubstituted compounds 1c and 1e at refluxing temperature to give 2a as the major product instead of the desired 2c and 2e. But, fortunately, we could obtain the desired products 2c and 2e without dechlorination in good yields (75 and 68%, respectively) when we carried out the reaction at lower temperature (140 C). We tried next the oxidation of 1a with iodine in methanol, which resulted in the formation of iodinated compound 3a (49%) instead of the expected 10-

Nucleoside Analogues from Branched‐Chain Pyranosides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and structural characterizations of para-bis(dialkyl/diarylphosphino)phenylenes built around tetrahalogenated benzene cores

Double deprotonation of 1,2-dibromo-4,5-difluorobenzene and 1-bromo-2-chloro-4,5-difluorobenzene by lithium diisopropylamide (LDA) in ethereal solutions is facile at very low temperatures ( T < −90 °C). The organo-dilithium intermediates thus generated react readily with chlorophosphines ClPR 2 (R = Ph and/or i Pr), producing 1,2-dibromo-3,6-bis(diphenylphosphino)-4,5-difluorobenzene ( 1a), 1,2-dibromo-3,6-bis(diisopropylphosphino)-4,5-difluorobenzene ( 1b) and 1-bromo-2-chloro-3,6-bis(diphenylphosphino)-4,5-difluorobenzene ( 1c). Corresponding P-oxides 2a– c are obtained by oxidation of 1a– c with H 2O 2. Analogous reactions of 1,2-dibromo-4,5-difluorobenzene and 1-bromo-2-chloro-4,5-difluorobenzene with only 1 equiv. of LDA do not result in selective monodeprotonations, as 1a and 1c are formed preferentially after ClPPh 2 quench. All of the isolated new compounds were fully characterized by multinuclear NMR spectroscopy, elemental analysis and/or mass-spectrometry. In addition, 1a, 1c, 2a, and 2b were characterized by single crystal X-ray diffraction methods.

New bisphosphinites from pamoic acid

Reaction of PhPCl2 with pamoic acid in a 2:1 molar ratio gives a bisphosphinite 5 as a conformational mixture of 5a and 5b which show different solubility in THF and Et2O. The less soluble biaxial conformer 5a was isolated spectrally pure, while it is very difficult to get pure biequatorial 5b without contamination of 5a. Oxidation of 5a with hydrogen peroxide/elemental sulfur or selenium gave the corresponding chalcogenides. The conformational features of the compounds were revealed by X-ray crystallography. In addition, two examples of complexes of 5a were prepared, the chelate complex [PtCl2{(5a)-P, P′}] and the bis-rhodium bridging complex from [RhCl2Cp*]2 dimer.

Ruthenium-Catalyzed Oxidation of Secondary Alcohols Assisted by a Simple Alkene

The oxidation of alcohols to carbonyl compounds has been recognized as a fundamental organic transformation in synthetic organic chemistry. Besides conventional routes, many elegant transition metal-catalyzed methods assisted by co-oxidants are known and used for such transformations. As part of our ongoing studies on ruthenium catalysis, it has recently been found that carbonyl compounds are coupled with alcohols in several routes. The coupling of ketones 1 with primary alcohols 2 preferentially afforded coupled ketones 4 (Scheme 1, route a) or coupled secondary alcohols 5 (Scheme 1, route b) according to the molar ratio of 2 to 1. In addition, secondary alcohols 3 was also found to be coupled with 2 to give 5 (Scheme 1, route c). Among them, in connection with this report, the addition of sacrificial hydrogen acceptor (1-dodecene) in the case shown in route c of Scheme 1 was essential for the dramatic enhancement of reaction rate. This could be due to the acceleration of initial oxidations of both starting alcohols by transfer hydrogenation from alcohols to 1-dodecene. Under these circumstances, this report describes a rutheniumcatalyzed oxidation of secondary alcohols in the presence of 1-dodecene. The results of several attempted oxidations of 1-(2naphthyl)ethanol (3a) to 2'-acetonaphthone (4a) under several conditions are listed in Table 1. Treatment of 3a in the presence of a catalytic amount of RuCl2(PPh3)3 (2 mol%) along with KOH in dioxane at 100 C afforded 4a in 15% isolated yield with 35% conversion of 3a (run 1). However, when 1-dodecene was further added, the oxidation rate was remarkably enhanced and 4a was formed in 77% yield with 85% conversion of 3a (run 2). As has been noted in our recent report, the fate of 1-dodecene seems to be partially converted into dodecane by accepting hydrogen. It is known that the carbon-carbon double bond of α,βunsaturated carbonyl compound works as a hydrogen acceptor for the ruthenium-catalyzed oxidation of secondary alcohols to ketones. Lower reaction temperature (80 C) resulted in a slightly lower yield of 4a (run 3). Performing the reaction under K2CO3/toluene in place of KOH/dioxane produced 4a in only 41% yield with incomplete conversion (43%) (run 4). Similar treatment of 3a in the presence of RhCl(PPh3)3 under the employed conditions resulted in lower yield of 4a (60%) when compared to the use of RuCl2(PPh3)3 catalyst (run 5). Given the controlled reaction conditions, various secondary alcohols 3 were employed to investigate the reaction scope. The results are summarized in Table 2. Aryl(methyl) carbinols (3b-3e) were oxidized into the corresponding ketones (4b-4e) in the range of 21-79% yields. The ketone yield was considerably affected by the electronic nature of the substituent on the aromatic ring of aryl(methyl) cabinols. With 3c and 3d having electron-donating substituent on the Scheme 1 Table 1. Oxidation of 3a into 4a under several conditionsa

A highly stereoselective preparation of CF 3-substituted 1-aryl-1,2-diphenylethenes: application to the synthesis of panomifene

β-CF 3-α,β-diphenylvinyl sulfide 3a was prepared stereoselectively in 77% yield from the reaction of 2 with phenyllithium at room temperature for 5 h. Oxidation of 3a with MCPBA afforded the corresponding vinyl sulfone 4a , in which ( E)- 4a can be crystallized in a mixture of CH 2Cl 2 and hexane. The addition–elimination reaction of ( E)- 4a with phenyllithium having substituents on the benzene ring provided 5a– j in 51–82% yields stereospecifically. Similarly, the treatment of ( E)- 4a with p-chloroethoxyphenyllithium in the presence of 12-crown-4 (20 mol %) at −10 °C, followed by slowly warming to room temperature, resulted in the formation of the corresponding panomifene precursor 6 in 82% yield.

Synthesis of Indeno[1,2-b]quinolin-10-ones via Pd/C-Assisted Dehydrogenation of 4b,5,10a,11-Tetrahydroindeno[1,2-b]quinolin-10-ones

Recently, we have reported the synthesis of 4b,5,10a,11tetrahydroindeno[1,2-b]quinolin-10-ones starting from the acetates of Baylis-Hillman adducts as in Scheme 1. Indenoquinoline derivatives showed a wide range of biological activities such as 5-HT-receptor binding activity, antiinflammatory activity, and also act as antitumor agents, inhibitor for steroid reductase, acetylcholinesterase inhibitors, and antimalarials. These compounds could be synthesized via the aza-Bergman cyclization or via the radical cyclization of isonitrile derivatives. In these contexts, development of a facile synthetic method of indeno[1,2-b]quinoline derivatives would be very important. Thus, we examined the possibility for the synthesis of a variety of indenoquinolines from 4b,5,10a,11-tetrahydroindeno[1,2-b]quinolin-10-one (1a) as shown in Scheme 2. Oxidation of 1a with iodine in methanol would produce 10methoxy-11H-indeno[1,2-b]quinoline. Treatment of 1a with POCl3 followed by dehydrogenation would generate 10chloro-11H-indeno[1,2-b]quinoline. Dehydrogenation of 1a with Pd/C or with related oxidant might produce indeno[1,2b]quinolin-10-one (Scheme 2). Treatment of 1a with POCl3 showed the formation of intractable mixtures, unfortunately. Oxidation of 1a with FeCl3 in methanol (reflux, 3 days) produced low yield of indeno[1,2-b]quinolin-10-one (2a, 21%). The use of 2.5 equivalents of DDQ (benzene, reflux, 10 h) for the oxidation of 1a showed moderate yield of 2a (52%). After many trials, we found that dehydrogenation conditions using Pd/C in refluxing decaline generate 2a in good yield (83%). As shown in Table 1, we prepared some indeno[1,2-b]quinolines 2b-e similarly by using Pd/C. It is noteworthy that dechlorination occurred simultaneously for the chlorinesubstituted compounds 1c and 1e at refluxing temperature to give 2a as the major product instead of the desired 2c and 2e. But, fortunately, we could obtain the desired products 2c and 2e without dechlorination in good yields (75 and 68%, respectively) when we carried out the reaction at lower temperature (140 C). We tried next the oxidation of 1a with iodine in methanol, which resulted in the formation of iodinated compound 3a (49%) instead of the expected 10-