Reaction Between Triphenylphosphine and Acetylenic Esters or Acetylenic Ketones in the Presence of Mercaptoesters

The reactive diionic intermediate generated by the addition of triphenylphosphine to electron-deficient acetylenic esters or ketones was trapped by mercaptoesters such as mercaptothioglycolate or methyl 3-mercaptopropanoate to produce substituted furans, vinyl sulfides, or dithioesters.     

Multicomponent Transformation of Isoindoline‐1,3‐diimine (=1H‐Isoindole‐1,3(2H)‐diimine), Acetylenic Esters,and Triphenylphosphine to Novel Dihydropyrimido[2,1‐a]isoindole Derivatives

The three‐component reaction of the zwitterions generated from dialkyl acetylenedicarboxylates (=dialkyl but‐2‐ynedioates and triphenylphosphine (Ph₃P) with isoindoline‐1,3‐diimine (=1H‐isoindole‐1,3(2H)‐diimine) is described (Scheme 1). This reaction affords the corresponding special type of substituted dihydropyrimido[2,1‐a]isoindole derivatives in good yields without using any catalyst and activation (Table).     

Cyanoacetylene and Its Derivatives: XXXIV. Nucleophilic Addition of Tetrazole to Cyanoacetylenes

Nucleophilic addition of tetrazole to 4-hydroxy-4-alkyl-2-alkynonitriles and to 3-phenyl-2-propynonitrile occurred regiospecifically and afforded E-, Z-4-hydroxy-4-methyl-3-tetrazolyl-2-alkenonitriles and 3-tetrazolyl-3-phenyl-2-propenonitrile [20–40°C, 13–50 h, 4–15 wt% MOH (M = Na, K), THF (or DMSO)] in up to 69% yield. The attempt to perform cyclization of the hydroxy-containing adducts into iminodihydrofurans (KOH, ethanol, 23-25°C) resulted in vinyl nucleophilic substitution of the tetrazole moiety by an ethoxy group.     

One-Step Synthesis of Electron-Poor Alkenes from Triphenylphosphine,Acetylenic Esters, 2,2,2-Trichloroethanol,and Ninhydrin

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 2,2,2-trichloroethanol leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce the corresponding chlorine-containing stabilized phosphorus ylides. An intermolecular Wittig reaction of the chlorine-containing stabilized phosphorus ylides with ninhydrin leads to the corresponding highly electron-poor chlorine-containing alkenes.     

One-Pot,Three-Component Synthesis of Dialkyl 1,2-Dihydroquinoline-2,3-Dicarboxylates from Triphenylphosphine,Acetylenic Esters,and Amide Derivatives of 2-Aminobenzaldehyde in Aqueous Acetone

Abstract

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by amide derivatives of 2-aminobenzaldehyde in the mixture of acetone-water (3:1) leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce the corresponding stabilized phosphorus ylides. An intramolecular Wittig reaction of the stabilized phosphorus ylide group with the aldehyde group leads to the corresponding dialkyl 1,2-dihydroquinoline-2,3-dicarboxylates.     

Synthesis of New Tetrazole Derivatives of Spiro‐ and Bis‐barbiturates

This work described the synthesis of the first and unprecedented examples of 5‐aryl‐1H‐tetrazoles including spiro‐ and bis‐(thio)barbiturates, generated from the reaction between 4‐(1H‐tetrazol‐5‐yl)benzaldehyde with (thio)barbituric acids and cyanogen bromide (BrCN) in the presence of triethylamine, providing good overall yields. Tetrazoles based on bis‐(thio) barbiturates were also obtained in the absence of BrCN under the same conditions. The structures were characterized by IR, ¹H NMR, ¹³C NMR, X‐ray crystallography and mass analysis techniques. The reaction mechanism was proposed. The hydrogen bond strength (E_HB) versus d (O1?????O7 (w)) distance (kcal.mol^?1) and corresponding pKa value for the proton of H_3A (in water molecule) in 4b.H₂O were estimated to be 13.8 kcal.mol^?1 and 8.2, respectively.     

Nonlinear Optical Properties of Porphyrin Derivatives with Electron‐donating or Electron‐withdrawing Substituents

To investigate photoelectric properties of meso‐extended porphyrin derivatives with electron‐donating or electron‐withdrawing substituents, a series of functionalized porphyrin materials have been designed and synthesized by Suzuki coupling reaction. The meso‐extended structures were fully characterized by ¹H NMR, IR spectroscopy and mass spectrometry. The photophysical properties of porphyrin derivatives were carefully examined by UV‐Visible and fluorescence spectra, and the solvatochromic effect was observed and discussed. In particular, Z‐scan technique was employed to characterize the third‐order nonlinear optical (NLO) properties of the products such as nonlinear absorption and refraction, the third‐order nonlinear refractive indexes (??⁽³⁾‐value) of these porphyrin derivatives achieved 3.9×10^?12 esu. In addition, the compounds could be self‐assembled into highly organized morphologies through phase‐exchange method. All the results indicated that the discotic materials have the potential for optoelectronic applications.     

Synthesis of Novel Pyrimidine Derivatives Containing the Vinylsulfanyl Group by Regio‐ and Stereoselective Addition of Thiouracils to Ethynyl Ketones

A regio‐ and stereoselective method for preparation of novel functionalized pyrimidine derivatives containing the vinylsulfanyl group has been developed based on addition reactions of 2‐thiouracils with phenylethynyl ketones. Reactions with ketones containing the disubstituted triple bond afford adducts of Z‐stereochemistry, whereas addition to ketone with the terminal triple bond gives preferentially products of E‐configuration.     

Regioselective and Stereoselective Synthesis of Pyridine‐Fused Benzoxepine Derivatives by Intramolecular Reductive Heck Cyclization [1]

An efficient method for the synthesis of 6,11‐dihydro[2]benzoxepino[4,3‐b]pyridine derivatives via Pd(0) catalyzed intramolecular reductive Heck cyclization is reported. The method offers the regioselective and stereoselective synthesis of highly functionalized pyridine‐fused benzoxepine derivatives in 75–85% yields under mild conditions. Chemoselective Sonogashira coupling is utilized for the synthesis of cyclization precursors. The stereochemistry of the exocyclic double bond of 6,11‐dihydro[2]benzoxepino[4,3‐b]pyridine derivatives is confirmed from single crystal X‐ray diffraction. The absence of N–Pd(II) interaction results in a reverse stereochemistry of the exocyclic double bond of dibenzoxepine derivative.     

Facile Regioselective Synthesis of 5‐Hydroxy‐4,5‐dihydroisoxazoles from Acetylenic Ketones

5‐Hydroxy‐4,5‐dihydroisoxazoles were synthesized conveniently in good yields by tandem conjugate addition‐cyclization reaction of acetylenic ketones and hydroxylamine hydrochloride salt.     

Synthesis of 4,5‐Dihydrofuran‐3‐carbonitrile Derivatives with Electron‐Rich Alkenes in the Presence of Manganese(III) Acetate

Radical cyclization reactions mediated by manganese(III) acetate were carried out with ν‐excessive alkenes ( 2a‐d ) and 3‐oxopropanenitriles ( 1a‐f ) resulting in the formation of 3‐cyano‐4,5‐dihydrofuran derivatives in poor to high yields. A mechanism was proposed for the cyclization reaction. The significance of the study is the formation of the 3‐cyano‐4,5‐dihydrofuran derivatives resembling terfuran, 2‐(2‐thienyl)furan and 2‐(2‐benzofuryl)furyl compounds having the fluorescent properties due to a conjugated ν‐electron system particularly containing the cyano moeity.     

One‐Pot Synthesis of Functionalized 3‐Aryl‐1‐phenyl‐1H‐pyrazoles from Hydrazonoyl Chlorides and Acetylenic Esters in the Presence of Ph3P

The zwitterionic 1 : 1 intermediates generated by addition of Ph₃P to acetylenic esters is trapped by 1‐[(aryl)chloromethylene]‐2‐phenylhydrazines (=N‐phenylarenecarbohydrazonoyl chlorides) to yield functionalized 3‐aryl‐1‐phenyl‐1H‐pyrazoles in good yields.     

Peptide‐Catalyzed Stereoselective Conjugate Addition Reactions of Aldehydes to Maleimide

The tripeptide H‐d Pro‐Pro‐Asn‐NH₂ is presented as a catalyst for asymmetric conjugate addition reactions of aldehydes to maleimide. The peptidic catalyst promotes the reaction between various aldehydes and unprotected maleimide with high stereoselectivities and yields. The obtained products were readily derivatized to the corresponding pyrrolidines, lactams, lactones, and peptide‐like compounds. ¹H NMR spectroscopic, crystallographic, and computational investigations provided insight into the conformational properties of H‐d Pro‐Pro‐Asn‐NH₂ and revealed the importance of hydrogen bonding between the peptide and maleimide for catalyzing the stereoselective C?C bond formation.     

Nickel‐Catalyzed Regioselective Hydroalkylation and Hydroarylation of Alkenyl Boronic Esters

Metal hydride catalyzed hydrocarbonation reactions of alkenes are an efficient approach to construct new carbon–carbon bonds from readily available alkenes. However, the regioselectivity of hydrocarbonation remains challenging to be controlled. In nickel hydride (NiH) catalyzed hydrocarbonation, linear selectivity is most often obtained because of the relative stability of the linear Ni–alkyl intermediate over its branched counterpart. Herein, we show that the boronic pinacol ester (Bpin) group directs a Ni‐catalyzed hydrocarbonation to occur at its adjacent carbon center, resulting in formal branch selectivity. Both alkyl and aryl halides can be used as electrophiles in this hydrocarbonation, providing access to a wide range of secondary alkyl Bpin derivatives, which are valuable building blocks in synthetic chemistry. The utility of the method is demonstrated by the late‐stage functionalization of natural products and drug molecules, the synthesis of an anticancer agent, and iterative syntheses.     

Synthesis and Electrochemical Behavior of Electron‐Rich s‐Tetrazine and Triazolo‐tetrazine Nitrate Esters

We have prepared energetic nitrate ester derivatives of 1,2,4,5‐tetrazine and 1,2,4‐triazolo[4,3‐b]‐[1,2,4,5]‐tetrazine ring systems as model compounds to study the electrochemical behavior of tetrazines in the presence of explosive groups. The model compounds showed lower thermal stabilities relative to PETN (pentaerythritol tetranitrate), but slightly improved mechanical sensitivities. The presence of electron‐rich amine donors leads to a cathodic shift of the tetrazine redox potentials relative to those of previously reported tetrazine explosives. At these potentials, electron‐rich tetrazines with either covalently bound or co‐dissolved nitrate ester groups are irreversibly reduced. Effectively, changes in the electronic structure of tetrazines affect their electrochemical response to the presence of nitrate ester groups. Thus, it may be possible to develop tetrazine‐based electrochemical sensors for the detection of specific explosives and electrocatalysts for their disposal.     

Enantio‐ and Regioselective Conjugate Addition of Organometallic Reagents to Linear Polyconjugated Nitroolefins

The copper‐catalysed conjugate addition of trialkylaluminium and dialkylzinc reagents to polyconjugated nitroolefins (nitrodiene and nitroenyne derivatives) is reported. A reversed Josiphos ligand L7 allows for the selective 1,4‐ or 1,6‐addition with high enantioselectivities.