Effects of metal coordination on the reactivity of 1,3,4-triphenyl-1,2-dihydrophosphete

Nucleophilicity dominates the reaction chemistry of 1,3,4-triphenyl-1,2-dihydrophosphete even when it is coordinated to electrophilic metal centers, but coordination dramatically alters the course of its reactions. Deoxygenation of carbonyl-containing substrates is effected by both the W(CO)₅ complex, which reductively couples benzaldehyde, and the HgCl₂ complex, which converts benzaldehyde to α,α-dichlorotoluene. Metal coordination appears to decrease the tendency of the dihydrophosphete to undergo electrocyclic ring opening to the corresponding 1-phosphabutadiene, and the HgCl₂ complex reacts with dimethyl acetylenedicarboxylate to afford a cyclopentadienyl ylide containing an intact dihydrophosphete unit. By reducing the nucleophilicity of the dihydrophosphete and/or the availability of the highly nucleophilic uncoordinated dihydrophosphete, coordination to HgCl₂ and W(CO)₅ makes accessible new mechanistic pathways. Dihydrooxaphosphinines, although unavailable through the reactions of the dihydrophosphete, may be synthesized by exploitation of the reactivity of organotitanium metallacycles. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:21–28, 1998     

Pyrolysis of 3-hydroxy-2-arylhydrazonoalkanoic acid derivatives

1,2-Diaza-1,3-butadienes have been obtained from readily available 3-hydroxy-2-arylhydrazonopropanoates under various reaction conditions including pyrolysis, dehydration under Mitsunobu conditions or with acetic anhydride or acetic acid. According to their method of synthesis these 1,2-diaza-1,3-butadienes underwent subsequent reactions to give interesting products, and in the presence of proper dienophiles gave the corresponding cycloaddition products. Also, a new approach to pyrazole-3-carboxylic acid derivatives was discovered during an attempt to dehydrate 3-hydroxy-2-arylhydrazonobutanoic esters.     

Chemistry of Dioxacyclanes: XI. Synthesis and Properties of Unsaturated Derivatives of 1,3-Dioxolanes

1'3-Dioxolanes were synthesized by reactions of 3-cyclohexenecarboxaldehyde, 5-norbornene-2-endo-carboxaldehyde with 1,2-ethanedithiol and 3-(2-propenyloxy)- and 3-propoxy-1,2-propanediols, aswell as of propionaldehyde, benzaldehyde, and trichloroacetaldehyde with the latter two thiols. Dichlorocarbene addition, bromination, and epoxidation of the ring C = C were accomplished, and activity of the resulting products as dienophiles in Dield-Alder reactions was assessed.     

(Z)-1,2-二苯基-1,3-丁二烯与单取代的乙烯衍生物区位选择性环加成反应

(Z)-1,2-二苯基-1,3-丁二烯分别与甲基乙烯基酮、丙烯酰胺、丙烯腈以及丙烯醛发生环加成反应,均生成顺式和反式的连位取代环己烯衍生物。以IR、¹HNMR和MS鉴定了产物的结构。利用CNDO/2法计算了分子轨道能量和系数,由前线分子轨道理论解释了这种环加成反应的区位选择性。     

Lateral extension of π conjugation along the bay regions of bisanthene through a Diels-Alder cycloaddition reaction

Diels-Alder cycloaddition reactions at the bay regions of bisanthene (1) with dienophiles such as 1,4-naphthoquinone have been investigated. The products were submitted to nucleophilic addition followed by reductive aromatization reactions to afford the laterally extended bisanthene derivatives 2 and 3. Attempted synthesis of a larger expanded bisanthene 4 revealed an unexpected hydrogenation reaction at the last reductive aromatization step. Unusual Michael addition was observed on quinone 14, which was obtained by Diels-Alder reaction between 1 and 1,4-anthraquinone. Compounds 1-3 exhibited near-infrared (NIR) absorption and emission with high-to-moderate fluorescent quantum yields. Their structures and absorption spectra were studied by density function theory and non-planar twisted structures were calculated for 2 and 3. All compounds showed amphoteric redox behavior with multiple oxidation/reduction waves. Oxidative titration with SbCl(5) gave stable radical cations, and the process was followed by UV/Vis/NIR spectroscopic measurements. Their photostability was measured and correlated to their different geometries and electronic structures.     

Nucleophilic displacement reactions at Se (II) : Reaction of areneselenenyl chlorides and 2-chloroalkyl phenyl selenides

The products of the title reaction depend upon the relative concentrations of reactants. With equimolar concentrations or an excess of 2-chloroalkyl phenyl selenide, the products are 1,2-dicloroethane and a diaryldiselenide. When excess areneselenenyl chloride is used ,the products are a diaryl diselenide and 2-chloroalkyl phenyl selenide dichloride. A mechanism involving nucleophilic displacement at selenenyl selenium is proposed to account for the observed products. Structural changes in the selenide or varying substituents in the 4-position of areneselenenyl chloride has little effect on the rate of the reaction. In the proposed continuum of mechanisms of nucleophilic displacement reactions at Se (II), an S_N2-like transition state best accounts for the data.     

Aminocatalytic Cross‐Coupling Approach via Iminium Ions to Different CC Bonds

Given the attractive ability of iminium ions to functionalize molecules directly at ostensibly unreactive positions, the reactivity of iminium ions, in which an α CH₂ group is replaced by C?O was explored. Background studies on the ability of such iminium cations to promote reactions via an iminium‐catalyzed or iminium‐equivalent pathway are apparently unavailable. Previously, tandem cross‐coupling reactions were reported, in which an iminium ion undergoes nucleophilic 1,2‐addition to give a putative three‐component intermediate that abstracts a proton in situ and undergoes self‐deamination followed by unprecedented DMSO/aerobic oxidation to generate α‐ketoamides. However, later it was observed that iminium ions can generate valuable α‐ketoamides through simple aerobic oxidation. In all reactions, iminium ions were generated in situ by reaction of 2‐oxoaldehydes with secondary amines.     

Rhenium-catalyzed synthesis of naphthalene derivatives via insertion of aldehydes into a C-H bond

A rhenium complex, [ReBr(CO)₃(THF)]₂, catalyzed reactions of aromatic ketimines and aldehydes with dienophiles, followed by dehydration, to give naphthalene derivatives in good to excellent yields. This reaction proceeds via C-H bond activation, insertion of an aldehyde, intramolecular nucleophilic cyclization, reductive elimination, elimination of aniline and Diels-Alder reaction. After dehydration, naphthalene derivatives were formed.     

Ring-Enlargement and Ring-Opening Reactions of 1,2-Thiazetidin-3-one 1,1-Dioxides with Ammonia and Primary Amines as Nucleophiles

The N-benzyl- and N-alkyl-substituted 1,2-thiazetidin-3-one 1,1-dioxides 1b – d reacted readily with NH₃ and primary amines via ring opening. The reaction with NH₃ proceeded at −78°→room temperature yielding ring-opened adducts via nucleophilic attack of NH₃ at the sulfonyl group, whereas the reactions with amines at room temperature yielded products via attack at the carbonyl group. The N-unsubstituted analogue 1a , when reacted with benzylamine in refluxing EtOH, also gave a product of ring opening via nucleophilic attack at the carbonyl group of 1a . The transamidation-like reactions of the 2-(aminoalkyl)-1,2-thiazetidin-3-one 1,1-dioxides 19a – d proceeded via six-, seven-, and eight-membered intermediates, giving the ring-enlarged eight-, nine-, and ten-membered products 21 – 24 (Schemes 8 and 9), respectively, in 42 – 87% yields. The products resulted from the nucleophilic attack of the amino group of the side chain at the carbonyl C-atom. The structure of the eight-membered product 24 with an asymmetrically situated methyl substituent was established by X-ray crystallography.     

Studies into the stereoselectivity of tartrate-derived dienophiles

[reaction: see text] Diels-Alder reactions of 1-(tert-butyldimethylsiloxy)-1,3-butadiene (3) with three C2 symmetric dienophiles derived from tartaric acid have been examined. Complementary diastereoselectivity is observed depending on the nature of the 1,2-diol protecting group incorporated in these dienophiles.     

One-pot synthesis of substituted indolo[1,2-a]quinolines under transition-metal-free conditions

A simple and efficient one-pot synthesis of substituted indolo[1,2-a]quinolines under transition-metal-free conditions has been developed. When 2-fluorobenzaldehyde was treated with substituted 2-methylindoles in the presence of Cs₂CO₃, the desired products were typically obtained in good to excellent yields. This reaction sequence involves a nucleophilic aromatic substitution and a Knoevenagel condensation reaction. Our mechanistic investigation revealed that both reactions could proceed as an intermolecular reaction in the first step.     

The insertion of sulfur and selenium into the 1,2-dihydrophosphete ring

Sulfur and selenium react with a 1,2-dihydrophosphete P-W(CO)₅ complex at ca. 120°C to give the corresponding 2,5-dihydro-1,2-thiaphosphole and 2,5-dihydro-1,2-selenaphosphole complexes, respectively. These products result from an insertion of S or Se into the P C sp³ bond of the four-membered ring.     

Reactions of polymerization-resistant 1,2-dithiolanes with lithiated oxygen heterocycles

Lithiated furans have been found to cleave the S–S bond of polymerization-resistant 1,2-dithiolanes to give the ring opened products in good yields. In the case of lithiated benzofuran, the excess reagent reacted with the normal product to give a mixture. Lithiated dihydrofuran and dihydropyran gave the corresponding ring-opened products that rearranged to spiro-1,3-dithianes during acidic workup. The reaction was applied to the selective synthesis of substrates for intramolecular Diels-Alder reactions. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:281–287, 1998     

Cycloadditionen von 3,4-Dimethoxyfuran an Dienophile

On cycloaddition reactions with 3,4-dimethoxyfuran We describe new cycloadditions of 3,4-dimethoxyfuran (3,4-DF, 1 ) with various dienophiles. In contrast to furan, the reaction of 3,4-DF with maleic anhydride gives exo- and endo-adducts at approximately the same rate. The thermodynamically more stable product is again the exo-product. Less active dienophiles lead also to mixtures of exo- and endo-adducts, except for citraconic anhydride (methylmaleic anhydride) which forms only the adduct with an endo-methyl group. Dimethylmaleic anhydride could not be reacted with 3,4-DF. All adducts with 3,4-DF contain a hidden 1,2-dicarbonyl group in the form of an endiolether. Its pronounced nucleophilic character allows a series of further additions. Noteworthy are the stereospecific cis-additions of halogens and the preparation of several acetals. Ozonolysis of the enolether in 4 allows the preparation of the hitherto unknown 2r, 3trans, 4trans, 5cis-tetrahydrofuran tetracarboxylic acid and derivatives thereof ( 5 and 6 ).     

Efficient syntheses of novel indeno[1,2-b]chromenone derivatives via hetero-Diels-Alder reactions of 2-(arylmethylene)-1H-indene-1,3(2H)-diones with enaminones

Efficient syntheses of novel 10-aryl-5a-(arylamino)-9-hydroxy-5a,6,7,8-tetrahydroindeno[1,2-b]chromen-11(10H)-one derivatives has been reported by [4+2] cycloaddition reactions of electron-deficient 2-(arylmethylene)-1H-indene-1,3(2H)-dione heterodienes with electron-rich enaminones in [bmim]BF₄ at 80?°C and in acetic acid at 80?°C. Dimedone/cyclohexane-1,3-dione enaminones have been used as dienophiles in Inverse Electron Demand hetero-Diels-Alder reactions. The products were obtained in high yields by a simple work up.     

Unexpected reaction pathways in the reaction of alkoxyalkynylchromium(0) carbenes with aromatic dinucleophiles

Thermal- or SiO(2)-induced reactions of the Michael adducts of 1,2-aromatic dinucleophiles and alkynylchromium(0) carbene complexes, compounds 7-10, form different products in good yields depending on the nature of the aromatic dinucleophile used. Thus, 1,2-diaminobenzene derivatives 7 and 8 rearrange to pentacarbonylchromium(0) isocyanide complexes 11, 12, 14, and 15 in a process that occurs through bicyclic intermediates 24. Adducts 9 derived from o-aminophenol give 2,3-dihydro-1,5-benzoxazepine derivatives 17 by intramolecular 1,2-addition, followed by protonation at the chromium center and reductive elimination. In contrast, base-promoted addition of the phenolic hydroxy group in compound 9 a affords 3-ethoxy-5-phenyl-5,6-dihydro-2H-1,6-benzoxazocin-2-one (18), together with the expected adduct 17 a. Compound 18 is formed by a nucleophilic addition to a CO ligand in a preformed carbene complex. This is a new example of the rare attack of a nucleophile on a CO ligand in a Fischer carbene complex. Adducts 10 form seven-membered-ring carbene complexes 19 and 20 by intramolecular aminolysis. In contrast, reaction of alkynyl carbene complexes with 1,8-diaminonaphthalene under very mild conditions leads to 2-substituted perimidines 33 together with the corresponding ethoxymethylmetal carbene complex 32 through an unprecedented fragmentation process in a formal retro-Aumann reaction.     

Versatile Cycloaddition Reactions of 1-Alkyl-1,2-Diphospholes

Abstract

The reactivity of 1-alkyl-1,2-diphospholes in cycloaddition reactions with dienes, dienophiles or 1,3-dipoles was examined. 1-Alkyl-1,2-diphospholes (2 ) exhibit dual reactivity and act as diene toward maleic acid derivatives or as dienophiles with 2,3-dimethyl-1,3-butadiene. The 1-alkenyl-1,2-diphospholes (4 ) are readily involved in intramolecular [4 + 2] cycloaddition reactions leading to cage phosphines (5 ). Interaction of 1-alkyl-1,2-diphospholes (2) with 1,3-dipolar reagents (diphenyldiazomethane and nitrones) results in formation of the bicyclic phosphiranes (8) and dimers of 1-alkyl-1,2-diphosphole oxides (9) or bicyclic phosphine oxides (10) with a β-lactam moiety depending on temperature.     

Reactions of carbanions derived from α-substituted-methyl tolyl sulfones with quinone methides as Michael acceptors

Nucleophilic addition of α-halo-4-tolylsulfonyl methyl anions to quinone methides and subsequent reactions were studied. Three kinds of consecutive reaction products were isolated, depending on the substrate structures and reaction conditions. Two of them were identified as rearrangement products and one as the vicarious nucleophilic substitution (VNS) product. An unexpected 1,2-migration of the tosyl group was observed. The mechanism of the reactions is briefly discussed.     

1,2-Thio group migration in Rh(II) carbene reactions

[reaction: see text] A series of beta-thio group substituted alpha-diazo carbonyl compounds have been prepared by nucleophilic substitution reactions of thiophenol, thionaphthol, or benzyl mercaptan with beta-acetoxy-alpha-diazo carbonyl compounds. The diazo decomposition of these diazo carbonyl compounds with various transition metal catalysts, including Rh(II) carboxylates and Cu(I) and Cu(II) complexes, has been investigated. It was found that the diazo decomposition of these compounds gave 1,2-thio group migration products. No 1,2-hydride or 1,2-aryl migration products were observed in all cases.     

Diels–Alder Reactions of 1,2‐Azaborines

Diels–Alder reactions employing 1,2‐azaborine heterocycles as 1,3‐dienes are reported. Carbocyclic compounds with high stereochemical and functional complexity are produced, as exemplified by the straightforward two‐step synthesis of an amino allyl boronic ester bearing four contiguous stereocenters as a single diastereomer. Whereas electron‐deficient dienophiles undergo irreversible Diels–Alder reactions, a reversible Diels–Alder reaction with the less electron‐deficient methyl acrylate is observed. Both the N and the B substituent of the 1,2‐azaborine exert significant influence on the [4+2] cycloaddition reactivity as well as the aromatic character of the heterocycle. The experimentally determined thermodynamic parameters of the reversible Diels–Alder reaction between 1,2‐azaborines and methyl acrylate correlate with aromaticity trends and place 1,2‐azaborines approximately between furan and thiophene on the aromaticity scale.