Degenerate and nondegenerate rearrangements of the 7-borabicyclo[..1]heptadiene system: Twofold [1,3] supra-facial sigmatropic migrations and anionic [1,] carbon-boron shifts

Two notable skeletal rearrangements of the 7-borabicyclo[..1]heptadiene system (III) have been uncovered: (1) a facile, degenerate, net twofold [1,] suprafacial sigmatropic migration of the 7-substituted boro group, observable by NMR spectroscopy when the carbon centers of the borole (I) and alkyne (II) bear suitable groups; and () a nondegenerate, anionic [1,] aryl shift from carbon to boron, converting the 7,7-dimethylborate salt of III into an aryl(dimethyl)pentaarylborate salt. Thus, the degenerate rearrangement was revealed when pentaphenylborole (Ia) was allowed to react with di-p-tolylacetylene (IIb) at 5°C; the resulting 7-borabicyclo[..1] heptadiene (III) formed displayed NMR methyl signals characteristic of p-tolyl groups located at both C⁵ and C⁶, as well as C⁴ and C⁵. Similarly, the nondegenerate, disruptive anionic isomerization of the 7,7-dimethylborate salt of IIIe or IVe was found to involve migration of either phenyl or p-tolyl groups from carbon to boron, showing that both phenyl (IIIe) and p-tolyl groups (IVe) were located at the bridgeheads in the precursors to VI.     

The first example of the generation of azomethine ylides from a fluorocarbene: 1,3-cyclization and 1,3-dipolar cycloaddition

The reaction of Schiff bases with fluorocarbene, generated by reduction of dibromofluoromethane with active lead in the presence of Bu₄NBr under ultrasound irradiation, involves the formation of fluoro-substituted azomethine ylides which undergo cyclization into aziridines. 1,3-Cyclization of ylides, generated from N-arylimines of benzaldehyde, proceeds stereoselectively. When carrying out the reaction of Schiff bases with fluorocarbene in the presence of dimethyl maleate or dimethyl acetylenedicarboxylate, the products of dehydrofluorination of the primary adducts of the 1,3-dipolar cycloaddition of fluoro-substituted azomethine ylides to multiple bonds of dipolarophiles were obtained. In the case of the reaction of N-alkylimines of benzaldehyde the cycloaddition of ylides to dimethyl maleate completely suppressed the cyclization to aziridines.     

Heterocycles derived from the condensation of 1,3-propanediamine with phthalic acid derivatives

The condensation of phthalic anhydride with 1,3-propanediamine afforded N-(o-carboxybenzoyl)-1,3-propanediamine (I) which by intravolecular cyclization was transformed into 2,3,4,6-b-tetrahydropyrimido[2,1-a]isoindol-6-one (II) rather than the benzodiazonine (III). An intermediate in the condensation is proposed. The reaction of 1,3-propanediamine with dimethyl phthalate also did not afford III, but rather a more complex product, dibenzo[c,l]-1,6,10,15-tetraazacyclooctadecane-5,11,16,22-tetraone (IX). Reaction of 1,3-propanediamine with phthaloyl chloride gave 6,13-propanodibenz[c,h]-1,6-diazecine-5,7,12,14-tetrone (XII). Spectroscopic data of the heterocycles obtained and chemical properties of II are given.     

Synthesis of 2-amino-1,3-dihydroxypropylphosphonates from Garner aldehyde

In the presence of triethylamine or ionic fluoride catalysts, the addition of dimethyl or diethylphosphite to Garner aldehyde proceeded with good (1:9) diastereoselectivity leading to a separable mixture of (1S,2S)- and (1R,2S)-hydroxyphosphonates. Almost equal amounts (43:57) of the respective phosphonates were formed when titanium(IV) isopropoxide was applied as a catalyst. The e.e.s of the hydroxyphosphonates reached 93–97% in the reactions catalysed by Ti(OiPr)₄ and dropped to 80–91% when triethylamine was used to catalyse the reaction.     

Manganese(III) acetate initiated oxidative free radical reaction between N-aroylindoles and dimethyl malonate

The manganese(III) initiated oxidative free radical reaction between N-aroylindoles and dimethyl malonate giving indolo[2,3-a]isoquinolines is described.     

Unusual steric effect of an alkenyl or aryl group on the dissociative reductive elimination from cis-alkenyl(or -aryl)dimethyl(triphenylphosphine)gold(III)

A sterically bulky aryl or alkenyl group directly bonded to gold suppresses the rate of dissociation of the triphenylphosphine ligand from cis-alkenyl(or -aryl)dimethyl(triphenylphosphine)gold(III) leading to selective reductive elimination.     

Synthesis and crystal structure of cobalt(II) complex with 2-diphenylacetyl-1,3-indandione

The structure of the synthesized compound of cobalt(II) with 2-diphenylacetyl-1,3-indandione (HL) and two dimethyl sulfoxide molecules was studied by X-ray single-crystal diffraction. One of the dimethyl sulfoxide molecules is disordered over two positions. Crystals of the compound are triclinic: Z = 2, space group P1, a = 11.510(6) Å, b = 11.686(6) Å, c = 16.667(8) Å, α = 93.14(1)°, β = 108.48(1)°, γ = 96.34(1)°. The deprotonated ligand molecules in the inner coordination sphere are located in the equatorial plane of the cobalt coordination polyhedron in the cis configuration. The two DMSO molecules are monodentate coordinated to the central atom through oxygen donor atoms and occupy axial positions.     

Synthesis of electron-poor 4-halo-2-azabuta-1,3-dienes by Rh(II)-catalyzed diazo ester-azirine coupling. 2-Azabuta-1,3-diene-2,3-dihydroazete valence isomerism

The Rh₂(OAc)₄-catalyzed reaction of alkyl 2-acyl-2-diazoacetates and dimethyl diazomalonate with methyl 2-bromo- and 2-chloro-3-phenyl-2H-azirine-2-carboxylates gives rise to electron-poor 4-halo-substituted (3E)-2-azabuta-1,3-dienes. Their formation proceeds with complete stereoselectivity via ring-opening of the intermediate azirinium ylide. 2-Azabuta-1,3-dienes with electron-withdrawing substituents at the 1,1,4-positions are stable compounds at room temperature, but are in equilibrium with cyclic valence isomers, 2,3-dihydroazetes, at elevated temperatures.     

Synthesis of 1,3-bis[(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)(dimethoxyphosphoryl)methyl]-4,6-dimethoxybenzene

A reaction of 1,3-dimethoxybenzene with dimethyl (3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidenemethyl)phosphonate gave rise to 1,3-bis[(3,5-di-tert-butyl-4-hydroxyphenyl)-(dimethoxyphosphoryl)methyl]-4,6-dimethoxybenzene, which was oxidized to 1,3-bis[(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)(dimethoxyphosphoryl)methyl]-4,6-dimethoxy-benzene.     

Synthesis and diels-alder reactions of e-1-trimethylsilylbuta-1,3-diene

A novel synthesis of E-1-trimethylsilylbuta-1,3-diene (1) has been achieved, and its Diels-Alder reactions with maleic anhydride, diethyl maleate, dimethyl fumarate, methyl propiolate, acrolein and acrylonitrile have been investigated. The structures of the products were studied to determine the stereoselectivity and regioselectivity of the reactions of this diene. In all cases with monosubstituted dienophiles the silyldiene 1 afforded the 1,3-disubstituted isomer (meta isomer) as the predominate regioisomer.     

Unusual reaction of 3-amino-1,2,4-triazole with 1,3-diiodopropan-2-one

3-Amino-1,4-bis(2-oxopropyl)-4H-1,2,4-triazolium triiodide is the product of the reaction of 3-amino-1,2,4-triazole with 1,3-diiodopropan-2-one in acetone in the absence of bases and phase-transfer catalysts. In dimethyl sulfoxide, conversely, a water soluble polyionene consisting of three aminotriazole rings bound by 1,3-dimethylenecarbonyl bridges is formed. The effect of the solvent on the alkylation of 3-amino-1,2,4-triazole with 1,3-diiodopropan-2-one was studied.     

Synthesis of 4H-1,3-benzoxazin-4-ones from 2,2-diazidobenzofuran-3(2H)-ones

Benzoxazine derivatives are useful building blocks and display various biological activities. We serendipitously discovered and subsequently developed a new one pot method for the synthesis of 2-(dimethyl amino)/2-morpholino/2- (piperidin-1-yl)-4H-benzo[e][1,3]oxazin-4-ones from corresponding substituted 2,2-diazidobenzofuran 3(2H) - ones and N-formyl dimethyl amine (DMF)/N-formylmorpholine/N-formylpiperidine using m-CPBA at 100?°C in moderate to good yields. We also demonstrated the utility of 4H-benzoxazines for the synthesis of other medicinally important compounds such as 2-hydroxyphenyl substituted 1,2,4-triazoles, unsymmetrical 1,3,5-triazines, and 1,2,4-oxadiazoles.     

2,2‐Dimethyl‐5‐nitroso‐1,3‐dioxan‐5‐yl benzoate, 2,2‐dimethyl‐5‐nitroso‐1,3‐dioxan‐5‐yl 4‐chlorobenzoate and 5‐nitroso‐1,3‐dioxan‐5‐yl 4‐chlorobenzoate

The crystal structures of 2,2‐dimethyl‐5‐nitroso‐1,3‐dioxan‐5‐yl benzoate, C₁₃H₁₅NO₅, (I), 2,2‐dimethyl‐5‐nitroso‐1,3‐dioxan‐5‐yl 4‐chlorobenzoate, C₁₃H₁₄ClNO₅, (II), and 5‐nitroso‐1,3‐dioxan‐5‐yl 4‐chlorobenzoate, C₁₁H₁₁NO₅, (III), have been determined in order to gain insight into the conformational preference of α‐benzoyloxynitroso. Unfavourable 1,3‐diaxial interactions force (I) and (II) to crystallize in the 2,5 twist‐boat conformation, whereas compound (III), lacking this destabilizing interaction, crystallizes in the chair conformation.     

Reaction of dialkyl 2-aryl-4-hydroxy-4-methyl-6-oxocyclohexane-1,3-dicarboxylates with aliphatic amines

Benzylamine, phenethylamine, and homoveratrylamine reacted with dialkyl 2-aryl-4-hydroxy-4-methyl-6-oxocyclohexane-1,3-dicarboxylates at the endocyclic carbonyl group with conservation of the enolic hydroxy group to give dialkyl 4-alkylamino-2-aryl-6-hydroxy-6-methylcyclohex-3-ene-1,3-dicarboxylates. The reaction of dimethyl 4-hydroxy-4-methyl-6-oxo-2-phenylcyclohexane-1,3-dicarboxylate with tryptamine was accompanied by dehydration with formation of dimethyl 4-[2-(1H-indol-3-yl)ethylamino]-6-methyl-2-phenylcyclohexa-3,5-diene-1,3-dicarboxylate, presumably due to basic properties of the indole nitrogen atom.     

Lipase-catalyzed resolution of anti-6-substituted 1,3-dioxepan-5-ols

Several anti-6-substituted 1,3-dioxepan-5-ols were kinetically resolved using an immobilized lipase (Amano PS–C II) in toluene in the presence of vinyl acetate at 30 °C. This approach provided, in some cases, the alcohol and the acetate in high enantiomeric purity, depending on the nature of the substituent (R = N₃, SePh, I, OBn) and the acetal group (unsubstituted or dimethyl). The role of the size of substituents is also discussed. Enantiopure anti-6-substituted 1,3-dioxepan-5-ols are useful building blocks.     

Speciation in the ternary system Iron(III)-nitrilotrimethylphosphonic acid-1,3-dicarboxypropane-1-iminodiacetic acid

The interaction of iron(III) ions with nitrilotrimethylphosphonic acid and 1,3-dicarboxypro-pane-1-iminodiacetic acid in aqueous solutions has been studied by spectrophotometry. It has been shown that complex formation in the system is complicated by protonation, hydrolysis, and precipitation. Homoligand 1: 1 complexes of different proton composition have been identified. The stability constants of the iron(III) complexonates and their fractional distribution as a function of pH (T = 20 ± 2°C, I = 0.1) have been determined. Conditions that make it possible to prevent the precipitation of iron(III) nitrilotrimethylphosphonates in the presence of 1,3-dicarboxypropane-1-iminodiacetic acid have been selected.     

Further study on 1,3-dialkylaminouracil with dimethyl acetylenedicarboxylate

On the treatment of 1,3-dialkyl-6-alkylaminouracil (1) with dimethyl acetylenedicarboxylate (DMAD), we were able to develop a new synthesis of deazapurine (pyrrolo[2,3-d]pyrimidine, 4) , and proposed the plausible mechanism for the formation of 3 and 4 from the adduct [dimethyl 2-(1,3-dialkyl-6-alkylamino-2,4-dioxopyrimidin-5-yl)fumarate, 2] of 1 with DMAD.     

Synthesis of 1-(2-Fluorophenyl)pyrazoles by 1,3-Dipolar Cycloaddition of the Corresponding Sydnones

3-Arylsydnones bearing fluorine and bromine atoms on the benzene ring were synthesized from N-nitroso-2-fluorophenylglycines and characterized by NMR spectroscopy. These were employed further in synthesis of the corresponding 1-(2-fluorophenyl)pyrazoles by 1,3-dipolar cycloaddition reaction with dimethyl acetylenedicarboxylate (DMAD) as activated dipolarophile. The sydnones as reaction intermediates were characterized by single crystal X-ray diffraction analysis showing interesting features such as halogen bonding as an important interaction in modeling the crystal structure.     

1,3-Dipolar cycloaddition of diazoalkanes onto dimethyl 1-(formylamino)ethylenephosphonate: a new route to 1-aminocyclopropanephosphonic acids and 3-phosphorylated pyrazoles

Diazoalkanes regiospecifically react with dimethyl 1-(formylamino)ethylenephosphonate (1a) to afford 5-substituted dimethyl 3-(formylamino)-4,5-dihydro-3H-pyrazol-3-phosphonates 2 in high yields. Their thermal decomposition followed by hydrolysis provides a straightforward access to 2-substituted 1-aminocyclopropanephosphonic acids 4. Aromatization of 2 under acidic conditions leads to 3-phosphorylated pyrazoles 5.     

3-Alkylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)-acrylonitriles as masked 1,3-dipoles

Reaction of 3-alkylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles with maleimides, dimethyl maleate and dimethylacetylene dicarboxylate were carried out to give octahydro-pyrrolo[3,4-a]pyrrolizin-4-ylidenes, hexahydro-pyrrolizines and 6,7-dihydro-5H-pyrrolizines. The formation of the synthesized compounds is explained by a 1,3-dipolar cycloaddition of an in situ generated azomethine ylide. The mechanisms of the formation of these active intermediates were discussed with the aid of density functional theory methods with the B3LYP functional 6-31G⁺ calculations using the STQN method and chemical experiments.