The structure of 1,2-dithioles studied by 13C n.m.r. spectroscopy

The charge separation between the dithiole ring and oxygen in 3-(1′,2′-dithiole-3′-ylidene)-6-methyl-2,3-dihydropyran-2,4-diones and 3-(1′,2′-dithiole-3′-ylidene)-2,3-dihydrobenzo[b] pyran-2,4-diones has been determined by ¹³C and ¹⁹F n.m.r. spectroscopy. By both methods it is found that these compounds are relatively polar. A correlation is established between the ¹³C chemical shift of some carbon atoms and the S2p binding energies measured by e.s.c.a. in the 1,2-dithiole derivatives. This correlation shows that these ¹³C shifts depend on the positive charge taken by the 1,2-dithiole ring and can then constitute a convenient evaluation of this charge.     

Unusual electron charge density in carboxylic acid. 17O quadrupole coupling in cis-cyclobutane-1,2-dicarboxylic acid

The (17)O NQR frequencies have been measured in cis-cyclobutane-1,2-dicarboxylic acid and the quadrupole coupling tensors have been determined at various temperatures. Two O···H oxygen positions and two O-H oxygen positions are observed, showing the presence of two different types of O-H···O hydrogen bonds in the unit cell. The quadrupole coupling constants at the O-H oxygen positions are approximately 30% lower than the lowest quadrupole coupling constants experimentally observed at the C-O-H positions in other carboxylic acids with either ordered or disordered hydrogen bonds. The O-H distances have been calculated from the (17)O-(1)H dipole-dipole interaction at the O-H oxygen positions. The obtained values are longer than the O-H distances usually found in O-H···O hydrogen bonds with comparable O···O distance, in agreement with the proposed proton exchange O-H···O ? O···H-O, which partially averages the dipole-dipole interaction. The energy difference of the two proton configurations, O-H···O and O···H-O, is calculated from the O-H distances determined by NQR. The temperature dependence of the (17)O quadrupole coupling tensors at the (17)O···H-O oxygen positions is analyzed in the model of proton exchange and the energy differences of the two proton configurations obtained by this analysis agree with the values obtained from the O-H distances. The quadrupole coupling tensors are analyzed in a model based on the Townes and Dailey model. The model shows that the population of an oxygen lone pair orbital is at this oxygen position reduced from 2 to approximately 1.3. The electron electric charge is most probably transferred to the oxygen σ and π electron orbitals. This may be associated with the structure of the cyclobutane ring, where the X-ray data show the presence of two unusually short C-C bonds.     

Sonogashira cross-coupling of 3-bromo-1,2-diones: an access to 3-alkynyl-1,2-diones

A new general method for the synthesis of enols of cyclic 3-alkynyl-substituted 1,2-diketones is developed. Sonogashira cross-coupling of silyl enolates of cyclic 3-bromo-cyclopentane- and 3-bromo-cyclohexane-1,2-diones with variety of substituted acetylenes afforded enols of cyclic 3-alkynyl-1,2-diones with good yields (up to 93%) in a short reaction time. The starting 3-bromo-1,2-diones are easily obtainable by direct bromination of 1,2-diones with NBS.     

Formic acid oxidatively cleaves 1,2,3,4-tetraaryl-2-butene-1,4-diones to 1,2-diaryl-1,2-ethanediones under microwave irradiation

Formic acid oxidatively cleaves 1,2,3,4-tetraaryl-2-butene-1,4-diones (1,2-aroylstilbenes) to 1,2-diaryl-1,2-ethanediones (benzils) under microwave irradiation. Mechanistic probing revealed that formic acid incorporates one of its oxygen atoms into benzil.     

1-Arylideneamino-2,2,2-trichloroethanols as synthetic equivalents of arylideneimines in the reaction with cyclopropenone derivatives

1-Arylideneamino-2,2,2-trichloroethanols react regiospecifically with cyclopropenones to form 2,2??-diaryl-1,1??,2,2??-tetrahydro-3H,3??H-2,2??-bipyrrole-3,3??-diones. A new preparative method was developed for the synthesis of 1-arylideneamino-2,2,2-trichloroethanols.     

Sulfoalkylation of 1,2-Dihydro-3,6-pyridazine- and 2,3-Dihydro-1,4-Phthalazinediones and Their N-Phenyl Derivatives by 1,3-Propanesultone and Bromoalkanesulfonates

When 1,2-dihydropyridazine-3,6-, 2,3-dihydrophthalazine-1,4-, 1-phenyl-1,2-dihydropyridazine-3,6-, and 2-phenyl-2,3-dihydrophthalazine-1,4-diones react with 1,3-propanesultone and bromoalkanesulfonates, depending on the nature of the sulfoalkylating agent in the case of 1,2-dihydropyridazine-3,6- and 2,3-dihydrophthalazine-1,4-diones, either N,O- or O,O1-disulfoalkylated compounds may be formed, while O-monosulfoalkylated reaction products may be formed in the case of the N-phenyl-substituted derivatives of the above-indicated azinediones.     

General synthetic entry to linearly-fused dihydrobenzocyclobutene-1,2-diones and benzocyclobutene-1,2-diones via annulation of 1,2-bis(methylene)carbocycles with 3-chloro-3-cyclobutene-1,2-dione

The tandem Diels-Alder/dehydrochlorination reaction of semisquaric chloride (1) with the 1,2-bis(methylene)cycloalkanes 2a-c and 1,2-bis(methylene)-4-cyclohexene (9) affords the linearly-fused cycloalkanodihydrobenzocyclobutene-1,2-diones 3a-c and 3,4,7,8-tetrahydrocyclobuta[b]-naphthalene-1,2-dione (10), respectively. On treatment with MnO2, 3a-c are dehydrogenated to the respective carbocycle-fused benzocyclobutene-1,2-diones 4a-c in good yields. 3a and 3b react with bromine to give the addition products 5a,b, which, on treatment with silver trifluoroacetate, afford the benzocyclobutene-1,2-diones 4a,b. For preparative purposes, the sequence 3-->5-->4 can be performed advantageously as a "one-pot procedure". Double-condensation reactions of 4a,b with alpha,alpha'-biscyano-o-xylene and o-phenylenediamine afford the pentacyclic biphenylenes 7a,b and the cyclobutahetarenes 8a,b, respectively. These cyclobutenediones suggest themselves as building blocks for the construction of extended linearly-fused polycyclic compounds with novel ring sequences. o-Quinodimethanes 12a-g generated in situ by the thermal decomposition of the respective 1,4-dihydro-2,3-benzoxathiin-3-oxides (sultines) 11a-g react with semisquaric chloride (1) to afford the 3,8-dihydronaphtho[b]cyclobutene-1,2-diones 13a-g. These, on dehydrogenation with bromine and/or MnO2, furnish the naphtho[b]cyclobutene-1,2-diones 14a-g in fair to good yields. As described for 4a,b the naphtho[b]cyclobutene-1,2-diones 14a-c are condensed with alpha,alpha'-biscyano-o-xylene and o-phenylenediamine to furnish the pentacyclic biphenylenes 15a-c and the pentacyclic cyclobutahetarenes 16a-c.     

Singly and Doubly Quinoxaline-Fused BIII Subporphyrins

B-Phenyl B^III subporphyrin-α-diones prepared in a three-step reaction sequence from the parent subporphyrin were condensed with 1,2-diaminobenzenes to give the corresponding quinoxaline-fused subporphyrins in variable yields. Quinoxaline-fused B-phenyl-5,10,15-triphenyl B^III subporphyrin was transformed to the corresponding subporphyrin-α-dione in the same three-step reaction sequence, which was then condensed with 1,2-diaminobenzene to give doubly quinoxaline-fused subporphyrin. These quinoxaline-fused subporphyrins exhibit redshifted absorption and fluorescence spectra compared with the parent one. A singly quinoxaline-fused subporphyrin bearing three meso-bis(4-dimethylaminophenyl)aminophenyl substituents shows blueshifted fluorescence in less polar solvent, which has been ascribed to emission associated with charge recombination of intramolecular charge transfer (CT) state.     

Regiospecific synthesis of α-chloro- and α-fluoro-1,2-diones

α-Chloro-1,2-diones and α-fluoro-1,2-diones were prepared from the corresponding α-chloroaldimines by a sequence of reactions involving cyanation to α-cyanoenamines, α-halogenation to form α-chloro- or α-fluoroimidoyl cyanides and addition of organolithium reagents across the nitrile moiety, followed by acidic hydrolysis. All steps are straightforward and occur without side reactions finally leading to regiospecifically chlorinated and fluorinated 1,2-diones in good yields.     

[4+2] Cycloaddition of 2(1H)-pyrazinones and 1,2,4-triazoline-3,5-diones

The reaction of 2(1H)-pyrazinones 1 and 1,2,4-triazoline-3,5-diones 3 was investigated by comparing that of 1 with singlet oxygen. 2(1H)-Pyrazinones 1 reacted in Diels-Alder fashion with 1,2,4-triazoline-3,5-diones 3 to afford [4+2]-adducts 4–17 in high yields.     

Synthesis of 1,2-disubstituted naphth [1,2-d]imidazole-4,5-diones

A convenient synthesis of 3-acylamino-1,2-naphthoquinones (I) is presented. The addition of aromatic and aliphatic amines to I followed by exposure to oxygen gives the corresponding 4-arylamino- or 4-alkylamino-3-acylamino-1,2-naphthoquinones (II). The addition of 4-cyclo-hexylbutylamine to 3-trichloroacetamino-1,2-naphthoquinone took an anomalous course and 1-(4′-cyclohexylbutyl)-3(H)-naphth[1,2-d]imidazoline-2,4,5-trione (VII) was obtained. Treatment of II with refluxing acetic acid gave 1,2-disubstituted naphth[1,2-d]imidazole-4,5-diones (III). The reaction was successful with a variety of 4-substituted amino-3-acylamino-1,2-naphthoquinones (II) and usually occurred in excellent yield. However, the cyclization of II to III is subject to steric limitation and attempts to cyclize 4-tert-butylamino-3-acetamino-1,2-naphthoquinone to the corresponding imidazole derivative was unsuccessful. The infrared, ultraviolet and nuclear magnetic resonance spectra of I, II, and III are discussed in relation to their structures.     

Semiconductor surface-induced 1,3-hydrogen shift: the role of covalent vs zwitterionic character

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to compare the reaction of 1,2-cyclohexanedione (1,2-CHD) with Si(001) and diamond(001) surface dimers under ultra-high-vacuum conditions. 1,2-CHD is known to undergo a keto-enol tautomerization, with the monoenol being the primary equilibrium species in the solid and gas phases. XPS and FTIR data demonstrate that 1,2-CHD reacts with diamond(001) through the OH group of the monoenol, resulting in only one O atom being bonded to the surface. In contrast, XPS and FTIR data suggest that both oxygen atoms in the 1,2-CHD molecule bond via Si-O-C linkages to the Si(001) surface dimer, and that the molecule undergoes an intramolecular 1,3-H shift. While the Si(001) and diamond(001) surfaces are both comprised of surface dimers, the diamond(001) dimer is symmetric, with little charge separation, whereas the Si(001) dimer is tilted and exhibits zwitterionic character. The different reaction products that are observed when clean Si(001) and diamond(001) surfaces are exposed to 1,2-CHD demonstrate the importance of charge separation in promoting a 1,3-H shift and provide new mechanistic insights that may be applicable to a variety of organic reactions.     

Synthesis of spiro[2H-indole-2,1′-1H-isoindole]-3,3′-diones,spiro[1H-isobenzofuran-1,2′-2H-indole]-3,3′-diones and spiro[benzofuran-2,1′-isobenzofuran]-3,3′-diones via transannular reactions of eight membered ring intermediates

An auto oxidation-rearrangement product 4 was isolated from a high dilution reaction of ninhydrin with 3,4,5-trimethoxyaniline in water. A general synthesis of this compound and its derivatives 4–6 was devised by oxidation of tetrahydroindeno[1,2-b]indol-10-ones 1–3 with sodium periodate to give isoindolo[2,1-a]-indole-6,11-diones 4–6 in good yield. Compounds 4–6 can be easily transformed into spiro[1H-isobenzofuran-1,2′-2H-indole]-3,3′-diones 8–10 , spiro[2H-indole-2,1′-1H-isoindole]-3,3′-diones 11–13 and isoindole[1,2-a:2′,1′-b]pyrimidine-5,15-diones 15, 16 in high yields. Analogous reactions were performed on 3-amino-5a, 10a-dihydroxybenzo[b]indeno[2,1-d]furan-10-one ( 17 ) to give a dibenzoxocintrione 18 , spiro-[benzofuran-2,1′-isobenzofuran]-3,3′-dione 19 and an isoindol-1-one 20 .     

1，2-环己二羧酸及芳香含氮配体的双核镉、锰配合物的合成和晶体结构

用水热法合成了两种新的配合物[Cd2(e,e-trans-chdc)2(bipy)2(H2O)2].H2O(1)和[Mn2(e,a-cis-chdc)2(phen)2(H2O)2].2H2O(2)(chdc=1,2-环己二羧酸,bipy=2,2′-联吡啶和phen=1,10-邻菲咯啉),用X-射线单晶衍射分析确定了配合物的晶体结构。配合物1和2均为双核分子。配合物1中,2个镉髤离子由2个1,2-环己二羧酸根以e,e-trans配位方式桥联,每个镉髤离子与1个2,2′-联吡啶的2个氮原子、2个1,2-环己二羧酸根的4个氧原子及1个水分子中的氧原子配位,形成了单帽变形三棱柱构型。配合物2中,2个锰髤离子由2个1,2-环己二羧酸根以e,a-cis配位方式桥联,每个锰髤离子与1个1,10-邻菲咯啉的2个氮原子、2个1,2-环己二羧酸根的3个氧原子及1个水分子中的氧原子配位,形成了畸变的八面体构型。配合物1和2分子之间都存在π-π堆积和O-H…O、C-H…O弱作用,进而将双核分子连接成三维超分子网络结构。配合物的荧光均来自于配体的荧光。     

3-acyl-1,2,3,4-tetrahydropyridine-2,4-diones: Synthesis and chemical properties

N-Substituted 6-methyl-1,2,3,4-tetrahydropyridine-2,4-diones reacted with aliphatic carboxylic acid chlorides in the presence of pyridine or triethylamine to give the corresponding 4-O-acyl derivatives which underwent O,C-migration of the acyl group by the action of 2 equiv of triethylamine and a catalytic amount of 2-hydroxy-2-methylpropanenitrile. Reactions of 3-acyl-6-methyl-1,2,3,4-tetrahydropyridine-2,4-diones thus formed with aliphatic and aromatic amines gave the corresponding enamino derivatives at the side acyl group. Enamino derivatives at the C⁴ =O group were obtained by transformation of 3-acyl-1,2,3,4-tetrahydropyridine-2,4-diones into 3-acyl-4-methoxy-6-methyl-1,2-dihydropyridin-2-ones via alkylation with dimethyl sulfate and subsequent treatment with amines.     

On the spectral similarity of bridging and nonbridging oxygen in tellurites

We show by high field (17)O solid-state nuclear magnetic resonance (NMR) and by ab initio calculations of both the NMR and the oxygen 1s photoelectron spectra that the oxygen sites in tellurite glasses show no spectroscopic distinction, even when comparing bridging and nonbridging sites. This is remarkable because two such sites differ formally by a full electronic charge, and they are readily distinguished by these same methods in silicates. We argue that this similarity arises from the symmetry breaking that occurs when the original TeO(2) crystal solid forms, due to the pseudo-Jahn-Teller distortion induced by the two additional valence electrons present in Te(IV) as compared to Si(IV).     

The unexpected and large enhancement of the dipole moment in the 3,4-bis(dimethylamino)-3-cyclobutene-1,2-dione (DMACB) molecule upon crystallization: a new role of the intermolecular CH...O interactions.

The molecular dipole moment of the 3,4-bis(dimethylamino)-3-cyclobutene-1,2-dione (DMACB) molecule and its enhancement in the crystal was evaluated by periodic RHF ab initio computations. A discrete boundary partitioning of the electronic density that allows an unambiguous partitioning of the molecular space in the condensed phase was adopted. The resulting molecular dipole in the crystal compares favorably with the experimental value obtained by a multipolar analysis of single-crystal X-ray diffraction data recorded at 20 K, using a fuzzy boundary partitioning of the derived pseudoatom densities. We show that a large and highly significant molecular dipole enhancement may occur upon crystallization, despite the lack of a strongly hydrogen bonded environment in the crystal. The 23 unique C-H...O interactions which are formed upon packing of the DMACB molecule induce an increase in the molecular dipole (over 75%) that is comparable to or greater than that found in systems which are characterized by the stronger O-H...O and N-H...O hydrogen bonds. The DMACB molecule constitutes an excellent system for the study of C-H...O interactions in the condensed phase, since no other kind of competing hydrogen bonds is present in its crystal. A simple and qualitative model for the matrix contribution to the DMACB molecular dipole enhancement in the crystal is proposed. The formation of several weak C-H...O bonds is found to yield a small (about 0.2 e) net flux of electronic charge flowing from the hydrogens of the methyl groups to the carbonyl oxygen atoms. Despite the limited increase of the intramolecular charge transfer upon crystallization, a large molecular dipole enhancement occurs because the centroids of the positive and negative induced charges are quite far apart. This work highlights a new and important role of the C-H...O bond, besides those already known in the literature.     

Synthesis of 1-substituted 1,2,3,4-tetrahydrobenz[g]isoquinoline-5,10-diones

1,2-Disubstituted 1,2,3,4-tetrahydrobenz[g]isoquinoline-5,10-diones are prepared for the first time through an activated Pictet-Spengler reaction of the corresponding imines of 2-(1,4-dimethoxynaphth-2-yl)ethylamine in the presence of an acyl chloride and AlCl(3) followed by an oxidation with silver(II) oxide in nitric acid. Depending on the reaction conditions the N-trichloroacetyl protecting group could be cleaved off, converted to an N-methoxycarbonyl group or transformed to an N-(2-oxoacetamide) moiety. The synthesized 1,2-disubstituted 1,2,3,4-tetrahydrobenz[g]isoquinoline-5,10-diones constitute a new class of quinones, which has not been reported yet.     

Copper(II)-catalyzed synthesis of benzo[f]pyrido[1,2-a]indole-6,11-dione derivatives via naphthoquinone difunctionalization reaction

Benzo[f]pyrido[1,2-a]indole-6,11-diones have been synthesized in high yields by copper(II)-catalyzed three-component reactions of acyl bromide, 1,4-naphthoquinone, and pyridine (or isoquinoline) via sp(2)-C-H difunctionalization of naphthoquinone followed by intramolecular cyclization and oxidative aromatization. In an attempt to expand the reaction scope and to help clarify the reaction mechanism, 1,3-dicarbonyl compounds are used in place of acyl bromides to take part in this reaction, and the benzo[f]pyrido[1,2-a]indole-6,11-diones derivatives are also obtained in excellent yields.     

Photooxidation of Diimine Dithiolate Platinium(II) Complexes Induced by Charge Transfer to Diimine Excitation

A photochemical and photophysical investigation was carried out on (tbubpy)Pt(II)(dpdt) and (tbubpy)Pt(II)(edt) (1 and 2, respectively, where tbubpy = 4,4'-di-tert-butyl-2,2'-bipyridine, dpdt = meso-1,2-diphenyl-1,2-ethanedithiolate and edt = 1,2-ethanedithiolate). Luminescence and transient absorption studies reveal that these complexes feature a lowest excited state with Pt(S)(2) --> tbubpy charge transfer to diimine character. Both complexes are photostable in deoxygenated solution; however, photolysis into the visible charge transfer band in air-saturated solution induces moderately efficient photooxidation. Photooxidation of 1 produces the dehydrogenation product (tbubpy)Pt(II)(1,2-diphenyl-1,2-ethenedithiolate) (4). By contrast, photooxidation of 2 produces S-oxygenated complexes in which one or both thiolate ligands are converted to sulfinate (-SO(2)R) ligands. Mechanistic photochemical studies and transient absorption spectroscopy reveal that photooxidation occurs by (1) energy transfer from the charge transfer to diimine excited state of 1 to (3)O(2) to produce (1)O(2) and (2) reaction between (1)O(2) and the ground state 1. Kinetic data indicates that excited state 1 produces (1)O(2) efficiently and that reaction between ground state 1 and (1)O(2) occurs with k approximately 3 x 10(8) M(-)(1) s(-)(1).