Synthesis of 3-thienyl substituted 2-pyrazolines by 1,3-dipolar cycloaddition

1,3,5-Trisubstituted 3-thienylpyrazolines have been prepared in high yields by the reaction of substituted,N-(P;-nitrophenyl)-3-thiophenecarbohydrazonoyl chlorides with Et₃N in CH₂Cl₂ in the presence of an excess of a monosubstituted olefin. The reaction probably occurs as 1,3-dipolar cycloaddition of the corresponding 3-thiophenecarbonitrile imines formedin situ at the double bond of the olefin.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 114–117, January, 1994.     

Cascade synthesis of pyrido[3,2-a]indolizines by reaction of Kröhnke–Mukaiyama salts with malononitrile dimer

An efficient protocol for the synthesis of highly functionalized 2-aminoindolizines and pyrido[3,2-a]indolizines has been achieved via the reaction of N-RC(O)CH₂-2-chloropyridinium bromides with 2-amino-1,1,3-tricyanopropene in the presence of Et₃N. The reaction of N-allyl-2-chloropyridinium bromide with 2-amino-1,1,3-tricyanopropene in the presence of Et₃N gives 3-[1-allylpyridin-2(1Н)-ylidene]-2-aminoprop-1-ene-1,1,3-tricarbonitrile, which could be cyclized to give [2-amino-(2-amino-3-vinylindolizin-1-yl)methylene]malononitrile upon treatment with KOH–DMF.     

Carbonylvanadium complexes of the tripod ligands MeC(CH2PPh2)3 and P(CH2CH2PPh2)3

UV irradiation of [Et₄N] [V(CO)₆] in the presence of the tripod ligands (L) MeC(CH₂PPh₂)₃ (cp₃) and P(CH₂CH₂PPh₂)₃ (pp₃) yields [Et₄N] [V(CO)₅L], cis-[Et₄N] [V(CO)₄L] and mer-[Et₄N] [V(CO)₃L] (where the meridional configuration for L = cp₃ is uncertain). Except for [Et₄N] [V(CO)₅cp₃], all these species were isolated. The complexes are characterized by their IR, ³¹P and ⁵¹V NMR spectra.     

Studies on uracils: synthesis of novel pyrido[2,3-d]pyrimidine oxides via ring transformation of isoxazolo[3,4-d]pyrimidine

The reaction of isoxazolo[3,4-d]pyrimidine 1 and cyanoolefins 2 in the presence of triethylamine (Et₃N) as a catalyst afforded an unprecedented one-pot synthesis of biologically important pyrido[2,3-d]pyrimidine oxides 3 in excellent yields.     

ortho-Formylation of oxygenated phenols

Oxygenated phenols are mono-formylated using a mixture of paraformaldehyde, MgCl₂, and Et₃N in THF. In all cases but one, only one regioisomer of the salicylaldehyde is obtained in good to high yield.     

MgCl2/Et3N Base System as a New Catalyst for the Synthesis of α‐Hydroxyphosphonate

An efficient and simple synthesis of α‐hydroxyphosphonates via reaction of aldehydes and ketones with dimethylphosphite in the presence of MgCl₂/Et₃N base system is reported. The use of readily available and easy to handle reagent MgCl₂/Et₃N makes this method simple, convenient, and practical.     

Ethynylmonocarba-closo-dodecaborates: M[12-HCC-closo-1-CB11H11] and M[7,12-(HCC)2-closo-1-CB11H10] (M = Cs, [Et4N])

Cesium and tetraethylammonium salts of the ethynyl functionalized monocarba-closo-dodecaborate anions [12-HCC-closo-1-CB₁₁H₁₁]⁻ and [7,12-(HCC)₂-closo-1-CB₁₁H₁₀]⁻ were obtained by desilylation of [Et₄N][12-Me₃SiCC-closo-1-CB₁₁H₁₁] and [Et₄N][7,12-(Me₃SiCC)₂-closo-1-CB₁₁H₁₀], respectively. Their thermal properties were examined by differential scanning calorimetry. The compounds were characterized by multi-NMR, IR, and Raman spectroscopy, (−)-MALDI mass spectrometry, and elemental analysis. Single-crystals of Cs[12-HCC-closo-1-CB₁₁H₁₁] and [Et₄N][7,12-(HCC)₂-closo-1-CB₁₁H₁₀] were studied by X-ray diffraction. The discussion of the spectroscopic and structural properties is supported by data derived from theoretical calculations using density functional theory as well as perturbation theory.     

Rearrangement of N-alkyl 1,2-amino alcohols. Synthesis of (S)-toliprolol and (S)-propanolol

N-alkyl 1,2-amino alcohols were rearranged stereospecifically by using TFAA/Et₃N. This rearrangement has been used to synthesize N-isopropyl-3-(aryloxy)-2-hydroxypropylamines, β-adrenergic blocking agents such as (S)-toliprolol and (S)-propanolol.     

Reaction of carbon disulfide with 2-bromoimidazolium salts. Novel bicyclic mesoionic thiazolo[3,2-a]imidazoles

A new class of thiazolo[3,2-a]imidazole derivatives is obtained in good yields, by reacting 1-methyl-2-bromoimidazolium salts bearing N⁺-CH₂COAr, N⁺-CH₂COMe, N⁺-CH₂COOMe, or N⁺-CH₂CN fragments, with carbon disulfide in the presence of Et₃N at room temperature. The mesoionic structures of these compounds are established by NMR spectroscopy and by single-crystal X-ray analysis.     

ortho-Formylation of estrogens. Synthesis of the anti-cancer agent 2-methoxyestradiol

Several estrogens were mono-formylated using a mixture of paraformaldehyde, MgCl₂, and Et₃N in refluxing THF. In all cases, the 2-isomer was formed as the major product with high regioselectivity compared to the 4-isomer. Excellent to high yields were obtained in all examples except one. The method was applied for an efficient synthesis of the anti-cancer agent 2-methoxyestradiol.     

Cationic polymerizations by aromatic initiating systems. II. Correlation between cationic model and polymerization reactions with the p-CH3C6H4CH2Cl/Et3Al system

Model experiments and subsequent polymerization runs have been carried out to elucidate the mechanism of cationic olefin polymerizations initiated by aromatic carbenium ions. Thus, the p-methylbenzylation of 2,4,4-trimethyl-1-pentene, a nonpolymerizable model olefin for isobutylene, was investigated by using the p-CH₃C₆H₄CH₂Cl/Et₃Al initiating system and CH₂Cl₂ solvent under various conditions. All the important organic reaction products were identified and most of them, quantitatively determined. Analysis of the nature of the products and their distributions gave important mechanistic information about the chemistry of elementary events and their relative rates; for example, hydridation and ethylation by the Et₃AlCl^? counteranion of various cations occurs and these processes mimic termination in carbocationic polymerizations. Hydridation and ethylation are much faster than proton elimination (chain transfer in polymerization) and experimental conditions (e.g., Al/Cl ratio and temperature) influence the relative rates of these processes. According to model experiments, the p-CH₃C₆H₄CH₂Cl/Et₃Al system may initiate olefin (isobutylene) polymerization; chain transfer to monomer should be relatively unimportant, but rapid hydridation or ethylation should reduce the kinetic chain and give low conversions. Predictions derived from model experiments were substantiated by polymerizations with isobutylene and the aromatic initiating system.     

Reactions of N-chloro-N-alkoxy-tert-alkylamines with isobutylene and methanol

The addition of N-chloro-N-methoxy-tert-alkylamines to an olefin, which is assumed to proceed with the participation of alkoxynitrenium ions, was carried out for the first time. The methanolysis of N-chloro-N-alkoxy-tert-alkylamines in the presence of Et₃N gives dialkoxyamines, and depending on the type of the N-alkyl substituent is accompanied by side reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1069–1072, May, 1991.     

An efficient copper-free Pd(OAc)2/Ruphos-catalyzed Sonogashira coupling of 1-chloroisoquinolines in the formation of 1-alkynyl-3-substituted isoquinolines

An efficient, copper-free Sonogashira coupling reaction of 1-chloroisoquinolines and terminal alkynes, catalyzed by Pd(OAc)₂/Ruphos, in the presence of Et₃N and tetrahydrofuran leads to the formation of 1-alkynyl-3-substituted isoquinolines in good yields.     

[Me8Pt4ReS4] and related PtMe2-containing clusters derived from tetrathiorhenate

The reactions of Pt₂Me₄(μ-SMe₂)₂ and [ReS₄]⁻ in MeCN solution have been investigated. The resulting polyalkylated clusters: Et₄N[ReS₄PtMe₂] (Et₄N[1]), Et₄N[ReS₄(PtMe₂)₂] (Et₄N[2]), and Et₄N[ReS₄(PtMe₂)₄] (Et₄N[4]), were characterized by ¹H, ¹³C, ¹⁹⁵Pt NMR spectroscopy and ESI mass spectrometry. The structure of Et₄N[1] was confirmed by single crystal X-ray diffraction, which demonstrated the expected square planar and tetrahedral coordination spheres bridged by a pair of sulfur atoms.     

Palladium-catalysed allylic amination for the direct synthesis of epi-4-alkylamino-N-acetylneuraminic acid derivatives

A simple and efficient procedure has been developed for the direct formation of epi-4-alkylamino-N-acetylneuraminic acid derivatives as potential inhibitors of influenza neuraminidases. The allylic amination of oxazoline 6 has been effected with a series of primary and secondary amines in the presence of catalytic Pd(π-allyl)₂(Et₃P)₂ to give the corresponding 4-epi-alkylamino products in a stereoselective and regiospecific manner.     

Carbon monoxide poisoning as a probe for the active site(s) of a nickel-based olefin oligomerization catalyst

The interaction of the olefin oligomerization catalyst system derived from [Ni(sacsac)(PBu₃)Cl] (sacsac = pentane-2,4-dithionate = dithioacetylacetonate) with carbon monoxide (CO) has been examined by a combination of ³¹P NMR and FTIR spectroscopy. The catalyst is rapidly and completely inhibited by CO; however, removal of the CO restores catalytic activity. A CO-adduct of the active catalyst has a characteristic CO stretching frequency of 2042 cm^?1, and δ³¹P 9.9 ppm. Carbon monoxide does not react with [Ni(sacsac)(PBu₃)Cl], but [Ni(sacsac)(PBu₃)(Cl)] reacts with any of Et₂AlCl, BuLi, Li[Et₃BH] or K[(s-Bu)₃BH] under an atmosphere of carbon monoxide in the presence or absence of olefin to produce [Ni(PBu₃)(CO)₃], which has been identified by FTIR and ³¹P NMR. [Ni(sacsac)(PBu₃)Cl] reacts completely with BuLi or K[(s-Bu)₃BH] to form catalytically inactive species which yield active catalysts on addition of Et₂AlCl.     

(1R,2R)-DPEN-derived triazolium salts for enantioselective oxodiene Diels-Alder reactions

Enantioselective oxodiene Diels-Alder reactions catalyzed by (1R,2R)-DPEN-derived triazolium salts were realized successfully. With 0.5 mol % of (1R,2R)-DPEN-derived triazolium salt C and 150 mol % of Et₃N, the reactions of various α-chloroaldehydes (α-bromoaldehyde) with substituted enones led to 3,4-dihydropyridinones and their derivatives in good yields, diastereoselectivities, and enantioselectivities (up to 97% ee).     

Modification of olefin polymerization catalysts. I. Mechanism of the interaction between AIEt3 and silyl ethers

The interaction between AlEt₃ and silyl ethers, Ph_nSi(OMe)_4-n (n = 0–3), was followed by ¹³C- and ²⁹Si-NMR techniques in conditions close to those typical for an olefin polymerization reaction with supported Ziegler–Natta catalysts (A1Et₃:silyl ether ratios from 1 to 10, temperature range 25–75°C). A1Et₃ and silyl ethers form instantaneously at ambient temperature a donor-acceptor complex, which is stable at a 1:1 molar ratio. In the presence of excess A1Et₃ the complex decomposes via a mechanism consisting, in the case of PhSi(OMe)₃, of five consecutive steps: alternating complexation and ether reductions with the formation of alkylated silyl ethers, Ph(Et)_nSi(OMe)_3-n (n = 1,2), and dialkyl-aluminum alkoxides, (Et₂A1OMe₃)_n (n = 2,3). The rate of decomposition was enhanced by the increasing number of methoxy groups present in the silyl ether, heating, or a high A1Et₃:silyl ether ratio. The decomposition was not inhibited by the presence of 1-hexene.     

Development of a 9-borabicyclo[3.3.1]nonane-mediated solid-phase Suzuki coupling for the preparation of dihydrostilbene analogs

A novel 9-borabicyclo[3.3.1]nonane-mediated solid-phase Suzuki coupling was developed to generate dihydrostilbenes (bibenzyls) and related compounds. Using optimized conditions (20 mol% PdCl₂(dppf), 10 equiv. Et₃N, and 10 equiv. olefin/9-BBN, in 9:1 DMF/H₂O, 50°C, 18 h), high conversions to desired products were generally obtained. A small combinatorial library of derivatives was successfully prepared via radiofrequency tagging and directed sorting techniques.     

Molybdenum and tungsten complexes with the heteroallyl-like Ph2P(O)C(S)NR− (R  Me,Ph) as ligand. X-ray structural analysis of Mo(CO)2(PPh3)(Ph2P(O)C(S)NPh)2 · CH2Cl2; A 4 : 3 piano-stool configuration

Ph₂P(O)C(S)N(H)R (R  Me, Ph) reacts with M(CO)₃(η⁵-C₅H₅)Cl (M  Mo, W) in the presence of Et₃N to give M(CO)₂(η⁵-C₅H₅)(Ph₂P(O)C(S)NR). The deprotonated ligand coordinates in a bidentate manner through N and S to give a four-membered ring system. M(CO)₃(PPh₃)₂Cl₂ (M  Mo, W) reacts with Ph₂P(O)C(S)N(H)R (R  Me, Ph) in the presence of Et₃N to give complexes in which the central metal atoms are seven coordinate through two ligands bonded via O and S to form five-membered ring systems, one PPh₃, and two CO groups. The complexes were characterised by elemental analyses, IR, ¹H NMR, and ³¹P NMR spectroscopy, and an X-ray structural analysis of Mo(CO)₂(PPh₃)(Ph₂P(O)C(S)NPh)₂ · CH₂Cl₂.