Regio- and diastereoselective cyclization reactions of free and masked 1,3-dicarbonyl dianions with 1,2-dielectrophiles

Despite their simplicity and synthetic usefulness, cyclisation reactions of 1,3-dicarbonyl dianions with 1,2-dielectrophiles are problematic, since both dianions and 1,2-dielectrophiles are highly reactive compounds (low reactivity matching). In addition, 1,2-dielectrophiles are often rather labile, and reactions with nucleophiles can result in polymerisation, decomposition, formation of open-chained products, elimination or SET-reactions. These intrinsic limitations can be overcome by a proper reactivity tuning and by the use of electroneutral dianion equivalents (masked dianions) in Lewis acid catalysed reactions. The cyclisations reported herein allow for an efficient, regio- and stereoselective one-pot synthesis of biologically relevant ring systems.     

Elucidation of π‐Conjugation Modes in Diarene‐Fused 1,2‐Dihydro‐1,2‐diborin Dianions

A series of diarene‐fused 1,2‐dihydro‐1,2‐diborins were prepared as a new B? B‐bond‐embedded polycyclic π‐electron system. The reduction of these compounds with metals produced their corresponding dianions, the π‐conjugation modes of which varied from 6π‐conjugation within the central 1,2‐diborin skeleton to 14π peripheral conjugation over the tricyclic skeleton, depending on the nature of the reduced biaryl framework. Moreover, the countercation to the dianions had a significant effect on the absorption spectra, with a dramatic color change from yellow to deep blue, depending on the distance between the tricyclic dianion skeleton and the countercation.     

Cyclobutene-1,2-diones. A Theoretical and Spectroscopic Study

The properties of substituted cyclobutene-1,2-diones 1 are examined by the use of (17)O NMR spectroscopy and theoretical calculations and compared to those of cyclopropenones 2 and other models. Cyclobutene-1,2-diones have less negative charge per oxygen compared to cyclopropenones, and electron donation by substituents enhances the negative charge on oxygen. Calculated (17)O chemical shifts reproduce the measured trends. The dianions of squaric and deltic acids are highly stabilized by negative charge delocalization to the oxygens.     

Vicinal diester dianions. Annelation with allylic and benzylic αω-dihalides. Synthesis of tricyclobuta[1,2:3,4:6,7]naphthalene

A new method of annelation utilizing the reaction of vicinal diester dianions with allylic and benzylic α,ω-dihalidesis described. The synthesis of tricyclobuta-[1,2:3,4:6,7] naphthalene is reported.     

A computational study of the lowest singlet and triplet states of neutral and dianionic 1,2-substituted icosahedral and octahedral o-carboranes

This work introduces a calibrated B3LYP/6-31G(d) study on the electronic structure of singlet and triplet neutral species of 1,2-substituted icosahedral 1,2-R(2)-1,2-C(2)B(10)H(10) and octahedral 1,2-R(2)-1,2-C(2)B(4)H(4) molecules with R = {H, OH, SH, NH(2), PH(2), CH(3), SiH(3)} and their respective dianions formed by proton removal on each R group. A variety of small adiabatic singlet-triplet gaps DeltaE(ST) are obtained from these systems ranging from 2.93 eV (R = NH(2)) 相似文献   

Functionalization of substituted 2(1H)- and 4(1H)-pyridones. III. The preparation of substituted 6-Vinyl-1,2-dihydro-2-oxo- and 1,4-dihydro-4-oxo-3-pyridinecarboxylic acids through the chemistry of pyridone dianions

The synthesis of various substituted 6-vinyl-1,2-dihydro-2-oxo-3-pyridinecarboxylic acids from the dianions of 1,2-dihydro-6-methyl-2-oxo-3-pyridinecarbonitrile and the corresponding 3-t-butyl ester is reported. The dianions were generated with LDA in THF at low temperature and reacted with various carbonyl substrates. Several conditions for the dehydration and hydrolysis of these adducts to the vinyl pyridone acids are discussed. Employing the conditions used for the 2-pyridone analogs, a series of substituted 6-vinyl-1,4-di-hydro-4-oxo-3-pyridinecarboxylic acids was prepared through the new dianion of 1,4-dihydro-6-methyl-4-oxo-3-pyridinecarboxylic acid, t-butyl ester.     

A one-pot synthesis of polysubstituted imidazo[1,2-a]pyridines

A series of 5,7,8-polysubstituted imidazo[1,2-a]pyridines were synthesized regioselectively from in situ generated α,β-unsaturated imines and dianions derived from methyl azolyl acetates in a one-pot procedure. The targeted molecules were conveniently isolated in analytically pure form (ca. 50-70% yields) by trituration of the concentrated reaction mixtures with cold ether.     

Kinetics of protonation of the 1,2-dinitrobenzene radical anion and dianion by phenol

The kinetics of protonation of electrochemically generated 1,2-dinitrobenzene (1,2-DNB) radical anions and dianions by phenol in DMF was studied by chronoamperometry. In the presence of phenol, the rate-determining step of electroreduction at the first wave potentials is the protonation of the 1,2-DNB radical anion with a rate constant of 103±13 L mol^s-1 s^s-1. The number of electrons involved in the process with phenol excess is 3, which corresponds to the formation of azoxy compounds. At the second wave potentials under these conditions, the electroreduction process is four-electron, which corresponds to the formation of 2-nitrophenyl-hydroxylamine, The rate constant for 1,2-DNB dianion protonation is 265±60 Lmol^s-1 s^s-1. The comparison of the experimental data with the results of quantum chemical calculation suggests the orbital control of the protonation reaction.     

Dilithiated phosphazenes: scaffolds for the synthesis of olefins through a new class of bicyclic 1,2-oxaphosphetanes

The first examples of the PN-directed dilithiation of (N-methoxycarbonyl)phosphazenes in the C(alpha) and C(ortho) to the phosphorus, and the use of these dianions in the formation of tri- and tetra-substituted olefins through stereospecific thermolysis of a new type of isolable bicyclic 1,2-oxaphosphetanes are described.     

Heteroaromatic annulation of 2-methyl/2-cyanomethylbenzimidazole dianions with alpha-oxoketene dithioacetals: a highly regioselective synthetic protocol for 1,2- and 2,3-substituted/annulated pyrido[1,2-a]benzimidazoles

A highly efficient and regioselective annulation protocol for a series of linearly 2,3- and angularly 1,2-substituted and annulated pyrido[1,2-a]benzimidazoles involving [3 + 3] cyclocondensation of the dianions generated from 2-methyl (2A) and 2-cyanomethyl (3A) benzimidazoles with a variety of alpha-oxoketene dithioacetals has been reported. Thus the dianion 2A derived from 2-methylbenzimidazole has been shown to undergo regioselective 1,2-addition with various alpha-oxoketene dithioacetals derived from acyclic (4a-d) and cyclic ketones (13a,b, 20, 29 and 32) to afford various carbinol acetals which on intramolecular cyclocondensation in the presence of phosphoric acid furnish the corresponding 1-methylthio-2,3-substituted (5a-c) and 2,3-fused linear polycyclic (14a,b,21, 30, and 33) pyrido[1,2-a]benzimidazoles in high yields. Similarly the dianion 3A from 2-cyanomethylbenzimidazole undergoes one-pot conjugate addition-elimination and cyclocondensation with these alpha-oxoketene dithioacetals to give 4-cyano-3-(methylthio)-1(or 1,2-)-substituted (6a-d) and the corresponding angularly 1,2-fused (16a,b, 23, 31, and 34) polycylic analogues of pyrido[1,2-a]benzimidazoles in excellent yields.     

Electron-transfer-induced reductive cleavage of chlorinated aryloxyalkanoic acids

We investigated the degradation of chlorinated herbicides, with an aryloxyalkanoic acid skeleton, under reductive electron transfer reaction conditions. Although Li and Na metals proved useless, activated forms of these metals, either their soluble naphthalene radical anions or 1,2-diarylethane dianions, promoted the degradation of the starting materials to various extents. Indeed, lithium naphthalenide promoted both extensive dehalogenation and dealkylation of chlorinated aryloxyalkanoic acids, with formation of the corresponding phenols as the main reaction products. In contrast, the employment of 1,2-diphenyl-1,2-disodioethane as a reducing agent led, in most examples, to the chemoselective recovery of the corresponding dechlorinated acids.     

Reaction and characterization of thioamide dianions derived from N-benzyl thioamides

Thioamide dianions were generated by the highly efficient reaction of N-benzyl thioamides with 2 equiv of BuLi. Alkylation, allylation, and silylation took place selectively at the carbon atom adjacent to the nitrogen atom of the thioamide dianions. Oxiranes and an aldehyde were also used as electrophiles in the reaction of thioamide dianions to form N-thioacyl 1,3- or 1,2-amino alcohols. The insertion reaction of elemental sulfur to a thioamide dianion and subsequent ethylation afforded a N-thioacyl hemithioaminal. NMR studies on the thioamide mono- and dianions derived from N-benzyl 2-methoxythiobenzamide showed a linear relationship between the chemical shifts of all carbon atoms of thioamide mono- and dianions. The results also suggested that the negative charge at the benzylic carbon atom of the dianion is not fully delocalized. The charge distribution patterns of the dianion are consistent with those of pi polarization.     

A comparison of the conductimetric behavior of cesium chloride in water-tetrahydrofuran,water-dioxane,and water-1,2-dimethoxyethane mixtures

The association constants of CsCl in water-THF, water-dioxane, and water-1,2-DME mixtures have been evaluated from conductance data using the Pitts, the Fuoss-Hsia, and a new conductance equation which includes the Chen electrophoretic effect. It is shown that the three sets of results confirm the Bjerrum concept of association. The differences observed for the ion association in the three types of mixtures are interpreted in terms of differences in the dipolar nature of the three organic molecules and that of H₂O.     

Strikingly long C...C distances in 1,2-disubstituted ortho-carboranes and their dianions

Neutral and especially dianionic 6- and 12-vertex closo ortho-carboranes (o-carboranes) 1,2-R2-1,2-C2BnHn (R = H, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, as well as e-, CH2-, NH-, O-, SiH2-, PH-, and S- exhibit extremely large variations (over 1 A!) of the cage CC distances, from 1.626 to 2.638 A, at the B3LYP/6-31G//B3LYP/6-31G DFT level. These CC "bond lengths," among the longest ever reported, generally are greater in the icosahedral than those in the corresponding octahedral systems and depend strongly on the substituents. While 1,2-(NH2)2-1,2-C2B10H10 has the longest Cc...Cc separation in neutral species (1.860 A), Cc...Cc distances can be much larger in the corresponding dianions. These range from 1.823 A (R- = e-) to 2.638 A (R- = CH2-) for 1,2-(R-)2-1,2-C2B10H10 and from 1.626 A (R- = SiH2-) to 3.099 A (R- = NH-) for 1,2-(R-)2-1,2-C2B4H4. Remarkably, there is no abrupt discontinuity over the entire range of CC lengths. Consequently, the relationship between the gradual changes in the distances and the nature of the bonding was analyzed by means of the form of the Kohn-Sham orbitals, the Wiberg Cc...Cc bond indices, and Bader AIM method. Cluster carboranes, and possibly other heteroboranes, thus appear to offer unique opportunities for modulating Cc...Cc distances.     

Anion radicals and dianions as electron transfer reagents

The catalytic regeneration of depolarizers by certain substrates has been demonstrated by means of cyclic voltammetry. As depolarizers we have employed anion radicals of aromatic hydrocarbons, heteroaromatic compounds, ketones, esters, nitriles, and olefins, and dianions of aromatic hydrocarbons, heteroaromatic compounds, ketones, and esters. As substrates we have investigated simple aromatic and aliphatic halides, 1,2- and 1,3-dihalides, carbon dioxide, and activated olefins. A requirement for the observation of a catalytic wave is that the reduced substrate undergoes a practically irreversible reaction after the reaction with the reduced depolarizer; for simple halides it is a cleavage reaction, for 1,2- and 1,3-dihalides an elimination, for carbon dioxide an addition, and for activated olefins a coupling. Electrochemical investigations of these kinds of reactions may be of interest in connection with the mechanism of several types of reactions in organic chemistry.     

Organolanthanoids V. The crystal and molecular structure of DI-η5-cyclopentadienyl-1,2-dimethoxyethaneytterbium(II)

Crystals of di-η⁵-cyclopentadienyl-1,2-dimethoxyethaneytterbium(II) are mono-clinic, space group Cc, with a 9.25(2), b 23.49(5), c 8.23(2) Å, β 123.59(4)° and Z  4. The ytterbium ion is pseudo-tetrahedrally coordinated by two cyclopentadienyl groups and a bidentate 1,2-dimethoxyethane ligand, and there is no inter-molecular association. The sites of the cyclopentadienyl ligands are disordered.     

Efficient synthesis of furan-2-ylacetates, 7-(alkoxycarbonyl)benzofurans, and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans based on cyclization reactions of free and masked dianions: a "cyclization/dehydrogenation" strategy

[reaction: see text] A variety of furan-2-ylacetates have been prepared by dehydrogenation of monocyclic 2-alkylidenetetrahydrofurans, which are readily available by cyclizations of open-chained 1,3-dicarbonyl dianions with 1-bromo-2-chloroethane. 5'H-[2,3']Bifuranyl-2'-ones are available based on sequential "cyclization/dehydrogenation" reactions of alpha-acetyl-gamma-butyrolactones. A variety of 7-(alkoxycarbonyl)benzofurans and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans were prepared by a cyclization/dehydrogenation strategy. These reactions rely on cyclizations of 2-oxocycloalkane-1-carboxylate-derived 1,3-dicarbonyl dianions ("free dianions") or 1,3-bis-silyl enol ethers ("masked dianions") with various 1,2-dielectrophiles.     

Voltammetric determination of facilitated ion transfer across the water/1,2-dichloroethane interface

The facilitated transfer characteristics of Cd²⁺ ion by 4-morpholinoacetophenone-4-ethyl-3-thiosemicarbazone (MAPET) across water/1,2-dicholoroethane (1,2-DCE) interface and its electrochemical properties were investigated by voltammetric measurements. Cyclic voltammetry (CV) was employed to examine the transfer in the conditions of the ligand (organic phase) in excess and the obtained transfer peaks have reversible nature at different metal concentrations and scan rates. The dependence of the obtained half-wave transfer potential on MAPET concentration showed that the equilibrium is effectively displaced towards a 1: 3 (Cd²⁺: ligand) stoichiometry with an association constant of logβ ₃ ⁰ = 12.96 ± 0.09 for the Cd²⁺ ion, corresponding to the TIC/TID mechanism.     

A facile synthesis of simple tetronic acids and pulvinones

Condensation of the dianions derived from simple α-hydroxyketones and 1,2-diketones with 1,1′-carbonyldiimidazole provides a facile one step synthesis of tetronic acids and pulvinones.     

Phenolic proton transfer to the 1,2 double bond in the molecular ion of trans-1,2-tetrahydrocannabinol

It is known that the molecular ion of trans-1,6-tetrahydrocannabinol (1,6-THC) with m/e 314 decomposes via a retro Diels-Alder reaction to fragment m/e 246, which then loses a Me radical to give the ion m/e 231 (cf Scheme 1).¹A similar breakdown is found for trans-1,2-tetrahydrocannabinol (1,2-THC), suggesting a shift of the double bond from the 1,2 to the 1,6 position in its molecular ion.Methylation of the phenolic OH group in trans-1,2-tetrahydrocannabinol however, shows that the phenolic proton transfer to the 1,2 double bond (cf Scheme 2) is much more important (～ 35–80%) than simple double bond migration (～ 20%; Scheme 3) in the formation of fragment m/e 231.