Copper‐Catalyzed Formal [4+2] Cycloaddition of Enoldiazoimides with Sulfur Ylides

Enoldiazoimides, a new subclass of enoldiazo compounds, generate enol‐substituted carbonyl ylides whose reactions with sulfur ylides enable an unprecedented formal [4+2] cycloaddition. The resulting multifunctionalized indolizidinones, which incorporate sulfur, are formed in good yields under mild reaction conditions. The uniqueness of this transformation stems from the role of the silyl‐protected enol, since the corresponding acetyldiazoimide failed to provide any cross‐products in metal‐catalyzed reactions with sulfur ylides. This copper‐catalyzed cycloaddition is initiated with the generation of enol‐substituted carbonyl ylides and sulfur ylides from enoldiazoimides and sulfonium salts, respectively, and proceeds through stepwise six‐membered ring formation, C?O and C?S bond cleavage, and silyl and acetyl group migration.     

Catalytic Asymmetric [ 2,3 ] -Sigmatropic Rearrangement of Sulfur Ylides Generated from Carbenoids

The catalytic asymmetric reactions of oxygen or sulfur ylides generated from carbenoids have attracted consider able attention in recent years. High enantioselectivities have been achieved in the 1,3-dipolar cycloaddition reactions and [ 2,3 ]-sigmatropic rearrangement of oxygen ylides. In contrast to the oxygen ylide, the corresponding catalytic asymmetric reaction of sulfur ylide is less developed. Compared to oxygen ylides, the sulfur ylides are more stable and experimental evidence supports a free ylide rather than a metal-bound ylide as reaction intermediate. That means the enantio-control must be in the step of the ylide formation. If the subsequent reaction such as [ 2,3 ]-sigmatropic rearrangement or 1,3-dipolar cycloaddition is a concerted process and is faster than the racemization of the chiral ylide intermediate, then the catalytic asymmetric sulfur ylide reaction will be possible.     

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.     

Asymmetric synthesis of multifunctionalized pyrrolines by a ruthenium porphyrin-catalyzed three-component coupling reaction

[reaction: see text] Chiral multifunctionalized pyrrolines have been synthesized by a ruthenium porphyrin catalyzed three-component coupling reaction. In a one-pot reaction, ruthenium porphyrins catalyzed in situ generation of chiral azomethine ylides from chiral diazo esters and imines. Asymmetric 1,3-dipolar cycloaddition reactions of the chiral azomethine ylides with dipolarophiles afforded the corresponding pyrrolines in good yields and high diastereoselectivity (up to 92% de).     

Rhodium(II)‐Catalyzed Enantioselective Synthesis of Troponoids

We report a rhodium(II)‐catalyzed highly enantioselective 1,3‐dipolar cycloaddition reaction between the carbonyl moiety of tropone and carbonyl ylides to afford troponoids in good to high yields with excellent enantioselectivity. We demonstrate that α‐diazoketone‐derived carbonyl ylides, in contrast to carbonyl ylides derived from diazodiketoesters, undergo [6+3] cycloaddition reactions with tropone to yield the corresponding bridged heterocycles with excellent stereoselectivity.     

Triphenylphosphine Mediated Simple Synthesis of Vinyl-Substituted Benzimidazoles

N -isopropenylbenzimidazolone undergoes a smooth reaction with triphenylphosphine and dialkyl acetylenedicarboxylates to produce highly functionalized salt-free phosphorus ylides in good yields. These stabilized phosphorus ylides exist as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides are converted to dialkyl 2-(1-isopropenyl-1H-benzimidazol-2-yl)-but-2-enedioates in boiling toluene.     

Reaction of chromone-3-carbaldehyde with α-amino acids—syntheses of 3- and 4-(2-hydroxybenzoyl)pyrroles

Azomethine ylides generated from the reaction of chromone-3-carbaldehyde with α-amino acids undergo 1,5-electrocyclization reactions to afford 3- and 4-(2-hydroxybenzoyl)pyrroles. These ylides can be trapped with dipolarophiles in 1,3-dipolar cycloaddition reactions to yield chromonyl pyrrolidines. The reaction of chromone-3-carbaldehyde with methyl glycinate gives a mixture of pyrrole, pyridine, and 3-aza-9-xanthenone derivatives.     

Decomposition of diazoketones in organic sulfides and sulfoxides: Cyclopropane formation from diazoketones via sulfonium ylides

The catalytic decomposition of diazoketones in the presence of organic sulfides and sulfoxides, gives sulfonium and sulfoxonium ylides as the primary reaction products, the final products isolated depending upon the relative nucleophilicity of the sulfides compared to that of the corresponding ylides, and on the stability of the ylides. The mechanism, scope and limitations of a new method of cyclopropane formation from diazoketones are discussed. Some circumstantial evidence supporting a concerted process for Wolff rearrangement is presented.     

Microwave-assisted synthesis of cyclopentanones using the relevant phosphorus ylides

A one-pot synthesis of cyclopentanone derivatives from phosphorus ylide under lab-type microwave assisted methodology was described. The phosphorus ylides were obtained via the reaction of activated acetylenic compounds, ethyl 4-chloroacetoacetate and triphenylphosphine. The structure of phosphorus ylides was assigned by 1H, 13C and 31PNMR. The phosphorus ylides as precursor were crystallized as two enantiomers (R,R) and (S,S) and one of the phosphorus ylide structures was confirmed by single X-ray crystallography.     

1,4-silatropy of S-alpha-silylbenzyl thioesters: a convenient route to silyl enol and dienol ethers accompanied by C-C bond formation via thiocarbonyl ylides

A novel convenient method for the generation of thiocarbonyl ylides from readily accessible starting materials and the first synthetic application of in situ generated ylides in the synthesis of silyl enol and dienol ethers, accompanied by C-C bond formation, is described. Under completely neutral conditions without any catalyst or additive, thermal reactions of S-alpha-silylbenzyl thioesters in sealed tubes at 180 degrees C provided silyl enol and dienol ethers in good to excellent yields with high stereoselectivities. This procedure consists of a multistep reaction in a one-pot process, i.e., 1,4-silatropy of S-alpha-silylbenzyl thioesters to give thiocarbonyl ylides, 1,3-electrocyclization of the ylides to give thiiranes, and the extrusion of sulfur from thiiranes to give silyl enol and dienol ethers.     

1,3-dipolar cycloaddition reactions of porphyrins with azomethine ylides

[reaction: see text] The behavior of porphyrins as dipolarophiles in 1,3-dipolar cycloadditions with azomethine ylides was studied. Depending on the nature of the substituent groups on the porphyrin macrocycles, the reaction can give monoadducts (chlorins) or bisadducts (isobacteriochlorins and bacteriochlorins). When a large excess of azomethine ylide is used, trisadducts can also be obtained. Mixed isobacteriochlorin derivatives were prepared from the reaction of azomethine ylides with the chlorin monoadducts previously obtained via Diels-Alder reactions.     

Synthesis of spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety via [3+2] annulation of carbon disulfide with Morita-Baylis-Hillman carbonates of isatins

Various spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety have been synthesized via [3+2] annulation reaction of carbon disulfide and the nitrogen ylides derived from Morita-Baylis-Hillman carbonates of isatins. 2,3-Dihydro- and 2,5-dihydrothiophene-2-thione moieties were formed selectively depending on steric hindrance around the nitrogen ylides.     

SYNTHESIS OF HIGHLY ELECTRON-POOR ALKENES FROM IN SITU GENERATED STABILIZED PHOSPHORUS YLIDES AND NINHYDRIN VIA INTERMOLECULAR WITTIG REACTION

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

An Improved Synthesis of a -Phenylseleno Arsonium Ylides

α -Seleno arsonium ylides 5 have been synthesized through the reaction of α -unfunctionalized arsonium ylides 4 with almost equimolar phenylselenenyl iodide 2.     

4-Methylpyrimidinium ylides. Part 7: 3+2 Dipolar cycloadditions to non-symmetrical substituted alkenes and alkynes

The ability of 4-methylpyrimidinium ylides (as 1,3-dipoles) to react with activated non-symmetrical substituted dipolarophiles (alkenes and alkynes) is presented. 4-Methylpyrimidinium ylides did not react with alkenes. With alkynes the reactions are regiospecific, a single regioisomer being obtained. A possible mechanism for the reaction pathway is proposed. For the first time in the pyrimidinium ylides series both isomers resulting from bonding to the 2-and 6-positions of the heterocycle ring were obtained. The appropriate conditions in order to increase the selectivity of one of the isomers were determined.     

Tributylphosphine-Catalyzed Stereoselective O-Vinylation of 2-Hydroxybenzaldehyde Derivatives

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between tributylphosphine and alkyl acetylenecarboxylates by 2-hydroxybenzaldehyde derivatives, leads to vinyltributylphosphonium salts, which undergo a Michael addition reaction with conjugate base to produce corresponding phosphorus ylides. The phosphorus ylides convert to electron-poor O-vinyl ether derivatives under reaction conditions.     

Three-Component Reaction Between Trivalent Phosphorus,Dimethyl Acetylenedicarboxylate,and Amide Derivatives

Stabilized phosphoranes were synthesized from the reaction between dimethyl acetylenedicarboxylate and amide derivatives in the presence of triphenylphosphine. Dimethylurea containing a phosphorus ylide underwent a smooth reaction in boiling toluene to produce hydantoin and oxo-oxazolidin containing stable phosphorus ylides in good yields. Phosphorus ylides derived from (PhO)₃P were not stable and converted to diastereoisomeric phosphonates and phosphorimidate. The nature of the amide derivatives and type of trivalent phosphorus compounds, as well as solvents, determined the distribution of products.     

Separation of semiconducting from metallic carbon nanotubes by selective functionalization with azomethine ylides

A mild and efficient method for the functionalization of SWNTs by cycloaddition of azomethine ylides derived from trialkylamine-N-oxides is described. Selective reaction of semiconducting carbon nanotubes was achieved by preorganizing the starting N-oxides on the nanotube surface prior to generating the reactive ylides. Separation of met-SWNTs from functionalized sem-SWNTs was successfully accomplished by inducing solubilization of sem-SWNTs in the presence of lignoceric acid.     

exo- and enantioselective cycloaddition of azomethine ylides generated from N-alkylidene glycine esters using chiral phosphine-copper complexes

High diastereo- and enantioselectivities were obtained for the asymmetric 1,3-dipolar cycloaddition of azomethine ylides generated from N-alkylideneglycine esters with dipolarophiles using chiral phosphine-copper complexes as catalysts. Whereas the cycloaddition of azomethine ylides catalyzed by metal salts generally afforded endo-adducts as the predominant product, the present method is the first example of an exo-selective cycloaddition. [reaction: see text]     

Triphenylphosphine Mediated Efficient Synthesis of 4-Substituted-1-methyl-2,5-dioxo-3-imidazolines

Summary.  Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between 1-methylparabanic acid (1-methylimidazoline-2,4,5-trione) and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine. These ylides exist in solution as a mixture of two geometric isomers. This is due to the restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides undergo smooth intramolecular Wittig reaction followed by an electrocyclic ring opening to produce dialkyl (E)-2-(1-methyl-2,5-dioxo-3-imidazolin-4-yl)-but-2-enedioates in good yields. Corresponding author. E-mail: isayavar@yahoo.com Received March 26, 2002; accepted (revised) April 24, 2002