Selenonium Ylides Research Articles

Selenonium ylides: synthesis, characterization, and applications to photo-induced cyclopropanation reactions.

Carbenes are important and highly reactive intermediates for the synthesis of various complex molecules. They are now an indispensable chemical species in organic chemistry and are used frequently to synthesize complex compounds in drug discovery chemistry. In general, carbenes are synthesized by a combination of transition metal catalysts and diazo compounds or by the decomposition reactions of diazo compounds. This paper reports the development of the visible light for the photochemical generation of carbenes from a novel C,Se-selenonium ylide. Overall, this photochemical carbene generation method using C,Se-selenonium ylide does not require a catalyst, is simple to perform, and enables highly efficient cyclopropanation reactions with alkenes.

Selenonium Ylides: Syntheses, Structural Aspects, and Synthetic Applications.

The goals of this mini review constitute (a) a presentation of the synthetic protocols applied to the preparation of achiral and non-racemic selenonium ylides; (b) discussion of their basic structural features, including their optical activity; and (c) a description of their synthetic applications in general synthetic methodology and in asymmetric synthesis.

Cu-Mediated arylselenylation of aryl halides with trifluoromethyl aryl selenonium ylides.

An unprecedented arylselenylation of aryl halides with trifluoromethyl aryl selenonium ylides in the presence of copper is described. The reaction proceeded at 100-140 °C under ligand- and additive-free conditions for 3-20 h to form a variety of unsymmetrical diaryl selenides in good to high yields. Arylselenylation is easy to operate, has good functional group tolerance, and demonstrates the different reaction profiles of trifluoromethyl aryl selenonium ylides from the homologous trifluoromethyl aryl sulfonium ylides.

Asymmetric synthesis of cyclopropyl phosphonates using chiral terpenyl sulfonium and selenonium ylides

The asymmetric cyclopropanation of a vinylphosphonate using optically active sulfonium and selenonium ylides derived from (−)-menthol and (+)-limonene was developed. The ylides were generated in situ by the reaction of the corresponding sulfonium or selenonium salt in the presence of potassium carbonate or DBU as a base. The transfer of the CHPh and CHCO2Et groups into the cyclopropane ring showed moderate diastereoselectivity and excellent enantioselectivity (up to 99:1) for the trans- and cis-products. The absolute configuration of phenyl cyclopropyl was assigned based on comparison to their tolyl analogues.

First Example of Highly Stereoselective Synthesis of 1,2,3‐Trisubstituted Cyclopropanes via Chiral Selenonium Ylides

As the first example of the application of chiral selenonium ylides in asymmetric cyclopropanation, a new strategy for the highly stereoselective synthesis of chiral 1,2,3-trisubstituted cyclopropanes via selenonium ylides is described. The reaction afforded three stereoisomers of chiral 1,2,3-trisubstituted cyclopropanes with good yields, excellent diastereoselectivities, very high enantioselectivities (up to >99% ee), good generality and recyclability of chiral selenides. The possible pathways and models of the asymmetric cyclopropanation via the chiral selenonium ylides were also proposed to rationalize the excellent enantioselectivities and diastereoselectivities.

New Camphor‐Derived Selenonium Ylides: Enantioselective Synthesis of Chiral Epoxides.

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New Camphor-Derived Selenonium Ylides: Enantioselective Synthesis of Chiral Epoxides

Optically pure selenonium salts 3 as the precursors of two new chiral selenonium ylides 4 can be synthesized stereoselectively from natural d-camphor in good yields. It is found that the reaction of the selenonium salt 3b, an aldehyde, and potassium tert-butoxide can take place smoothly in ‘one-pot’ via the formation of selenonium ylide 4b, to give chiral trans-diaryl epoxides 5 in good yields with good diastereoselectivities and enantioselectivities.

First chiral selenium ylides used for asymmetric conversion of aldehydes into epoxides.

Enantioenriched selenonium ylides have been generated by addition of benzyl bromide to C2 symmetric (2R,5R)-2,5-dimethylselenolane in the presence of NaOH, and subsequently reacted with a variety of aldehydes to give oxiranes with excellent enantiomeric excesses (a catalytic version has been achieved); also, an aliphatic cyclic hypervalent dibromoselenurane structure has been demonstrated by X-ray analysis.

Reactions of 2‐(Organylseleno)propenenitriles with Dimethyl Ethynedicarboxylate

Abstract(2‐tert‐Butylseleno)propenenitrile (12a) has been prepared and treated with dimethyl ethynedicarboxylate (3) and methyl propiolate (18) to give the 2,3‐dihydroselenophenes 16 and 21, respectively. In contrast, 2‐(ethylseleno)‐, 2‐(methylseleno)‐ and 2‐(phenylseleno)propenenitrile (12b–d) tend to form polysubstituted butadienes 17b–d with 3 by net organoylseleno group transfer from 12b–d to C‐2 of 3 following attachment of C‐3 of 17 to C‐3 of 3. Five‐membered selenonium ylides are proposed as intermediates.

ChemInform Abstract: Nucleophilic Substitution Reaction of Optically Pure Chloroselenurane with Active Methylene Compounds. Formation of Optically Pure Selenonium Ylides.

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Nucleophilic Substitution Reaction of Optically Pure Chloroselenurane with Active Methylene Compounds. Formation of Optically Pure Selenonium Ylides

Abstract Nucleophilic substitution reaction of (RSe)-chloroselenurane 1 with active methylene compounds proceeded in highly stereoselective manner with retention of configuration to give (SSe)-selenonium ylides 2. (SSe)- and (RSe)-Ylides, 2 and 3, were stereospecifically formed from the reaction of (RSe)- and (SSe)-selenoxides, 4 and 5, with active methylene compounds.

Activation energies for pyramidal inversion of sulfonium selenonium and telluronium ylides based on ab initio MO calculations

Ab initio MO calculations of sulfonium, selenonium and telluronium ylides R12X+–C–R22(X = S, Se, Te; R1= H, Me; R2= H, CN) have been performed to estimate their thermal stabilities toward the pyramidal inversion (vertex inversion) reaction. Geometrical parameters at both the global minima and the saddlepoints are independent of the levels of theory employed. However, the activation energies for the pyramidal inversion reaction depend on the levels of theory employed; a method superior to the Hartree–Fock level of theory was necessary for the present purposes. The activation energies for the pyramidal inversion were also found to depend on the substituents. The present computations clearly indicate that the telluronium ylides require higher activation energies for the pyramidal inversion reaction than those of the sulfonium and selenonium ylides.

Stable selenoxanthenium ylides : synthesis and new reductive cyclization of selenoxanthen-10-10(alkoxalyl alkoxycarbonyl)methanides and their related compounds

Stereoisomers of 9-substituted selenoxanthen-10-io (alkoxalyl alkoxycarbonyl)methanides were prepared from the corresponding selenoxides and activated acetylenes. In the reaction of 9-phenylselenoxanthene 10-oxide( 1c ) with methyl propiolate afforded an unexpected product, methyl 9-phenylselenoxanthen-9-ylpropiolate( 5 ) together with ylide( 2e ). The selenonium ylides underwent new reductive cyclization with sodium borohydride to afford new cyclic selenonium ylides.

Synthetic routes to cyclopropylidenecarbinols and to cyclopropylidienes

Functionalized alkylidine cyclopropanes have beeen prepared from 1-seleno 1-vinyl cyclopropanes using [2,3] sigmatropic rearrangement of their corresponding selenonium ylides. A comparison with sulphur analogues is presented.

Nitro ylides. 7. Synthesis and some reactions of alkyl-substituted selenonium nitro ylides

1. Stable dialkylselenonium nitro ylides have been synthesized. 2. In reactions with strong electrophilic reagents (halogens, hydrogen halides, and N-halo imides), the dialkylselenonium nitro ylides behave like their diphenylselenonium analogs: cleavage of the intermediate selenonium salt by the counterion and by a second molecule of electrophile takes place exclusively at the\(Se--C_{NO_2 } \) bond. 3. A study has been made of the ability of iodonium nitro ylides to transfer a nitromethylene fragment to sulfides and selenides to form the corresponding sulfonium and selenonium ylides. 4. The feature distinguishing the dialkylselenonium nitro ylides from their diaryl analogs is their ability to undergo a transylidation reaction with thiourea.

Reaction of carbonyl-stabilized selenonium ylides with derivatives of some group V trivalent elements

1. The “iodonium method” is an efficient way of synthesizing the selenonium ylides: 2-methylphenylselenuranylidenedimedon and methylphenylselenuranylidenedibenzoylmethane. 2. Similar to S-alkyl-substituted sulfonium ylides, 2-methylphenylselenuranylidenedimedon and methylphenylselenuraaylidenedibenzoylmethane when treated with Et3N or Ph3As in the presence of NaBPh4 are demethylated to give the corresponding ammonium and arsonium tetraphenylborates.

ChemInform Abstract: ADDITIONS OF DIBENZYL SELENOXIDES AND SELENONIUM YLIDES TO AN ELECTRON‐DEFICIENT ETHYLENE AND ACETYLENE

AbstractDie Dibenzylselenoxide (III) reagieren mit Dimethylacetylencarboxylat (II) und Tetracyanoäthylen (IV) zu den neuen Yliden (I) bzw. (V); neben (V) entstehen die Selenocyanide (VI) sowie entsprechende Selenide.

Additions of Dibenzyl Selenoxides and Selenonium Ylides to an Electron-Deficient Ethylene and Acetylene

Abstract Dibenzyl selenoxides reacted with dimethyl acetylenedicarboxylate and tetracyanoethylene to give new ylides, while the reaction of selenonium ylides produced new ylides or cyclopropane derivatives.

ChemInform Abstract: A NOVEL TETRAMETHYLTHIOUREA‐CATALYZED DECOMPOSITION OF STABILIZED SELENONIUM YLIDES

A few stabilized selenonium ylides react with a catalytic amount of tetramethylthiourea in the presence of acetic acid at room temperature to give the corresponding selenides and olefins in good yields.

A NOVEL TETRAMETHYLTHIOUREA-CATALYZED DECOMPOSITION OF STABILIZED SELENONIUM YLIDES

Abstract A few stabilized selenonium ylides react with a catalytic amount of tetramethylthiourea in the presence of acetic acid at room temperature to give the corresponding selenides and olefins in good yields.