Allylic Selenides Research Articles

Electrochemical Stereoselective Synthesis of (Z)‐Allyl Aryl Selenides and Sulfides from Baylis‐Hillman Acetates

AbstractThis research presents a method for the oxidative selenylation and thiolylation of Morita‐Baylis‐Hillman adducts through constant‐current electrolysis in an undivided cell at room temperature. The reaction enables direct production of trisubstituted (Z)‐allyl aryl selenides and sulfides with yields of 27–98%. A wide variety of different functionalities are well tolerated under these reaction conditions. This strategy could be carried out on gram scale and several synthetic transformations were accomplished for the construction of other allyl selenide derivatives. Control experiments and mechanistic studies indicate a radical or an ionic addition pathway for this electrochemical transformation.

Thermally Driven Diselenide Metathesis: Polarization Process vs Radical Process.

Diselenide, as a dynamic covalent bond, has been widely applied in functional materials due to its response to light, heat, sonication, pH, and other stimuli. Herein, a polarization-induced metathesis mechanism for diselenides under heating conditions in the dark is proposed. First, a radical trap experiment is used to prove that the exchange reaction of diselenides in the dark does not involve any radicals. Second, the dynamic exchange reaction of diselenides is found to be affected not only by the polarity of the solvent but also by the introduction of polar groups into the molecular skeleton. Furthermore, DFT calculations also support the notion that polarity has a large effect on the heterolytic rather than homolytic bond dissociation energies. The experimental results for allyl selenide small molecules, polymers, and polymer materials catalyzed by diselenide all support the polarization-induced metathesis mechanism. In short, we successfully enhanced the understanding of the mechanism for diselenide metathesis.

Photoresponsive dynamic covalent bond based on addition–fragmentation chain transfer of allyl selenides

A new dynamic covalent bond allyl selenide that can undergo a reversible addition–fragmentation chain transfer reaction under ultraviolet irradiation.

Chiral Cobalt(II) Complex Catalyzed Asymmetric [2,3]-Sigmatropic Rearrangement of Allylic Selenides with α-Diazo Pyrazoleamides

Organoselenium compounds, due to their high structural diversity, special function, and biological activities, have drawn attention in synthetic chemistry. Herein, a novel example of chiral N,N′-di...

Intramolecular Thioether Migration in the Rhodium‐Catalyzed Ene‐Cycloisomerization of Alkenylidenecyclopropanes by a Metal‐Mediated β‐Sulfide Elimination

AbstractReported is the first example of a rhodium‐mediated β‐sulfide elimination, which represents a new mode of reactivity for late‐transition‐metal chemistry. This serendipitous discovery facilitates an ene‐cycloisomerization of allylic‐sulfide‐containing alkenylidenecyclopropanes (ACPs) to afford five‐membered carbo‐ and heterocyclic rings with concomitant intramolecular thioether migration. Interestingly, similar selectivity is obtained with both E‐ and Z‐allylic sulfides and the reaction is also feasible with an allylic selenide. Mechanistic studies are consistent with an inner‐sphere transfer of the sulfide, which is remarkable given the propensity for sulfides to poison transition‐metal catalysts. Finally, this type of atom‐economical rearrangement is envisioned to prompt the development of related processes given the utility of sulfides in target‐directed synthesis.

Intramolecular Thioether Migration in the Rhodium-Catalyzed Ene-Cycloisomerization of Alkenylidenecyclopropanes by a Metal-Mediated β-Sulfide Elimination.

Reported is the first example of a rhodium-mediated β-sulfide elimination, which represents a new mode of reactivity for late-transition-metal chemistry. This serendipitous discovery facilitates an ene-cycloisomerization of allylic-sulfide-containing alkenylidenecyclopropanes (ACPs) to afford five-membered carbo- and heterocyclic rings with concomitant intramolecular thioether migration. Interestingly, similar selectivity is obtained with both E- and Z-allylic sulfides and the reaction is also feasible with an allylic selenide. Mechanistic studies are consistent with an inner-sphere transfer of the sulfide, which is remarkable given the propensity for sulfides to poison transition-metal catalysts. Finally, this type of atom-economical rearrangement is envisioned to prompt the development of related processes given the utility of sulfides in target-directed synthesis.

ChemInform Abstract: [2,3]‐Sigmatropic Rearrangement of Allylic Selenimides: Strategy for the Synthesis of Peptides, Peptidomimetics, and N‐Aryl Vinyl Glycines.

AbstractThe scope of the NCS‐mediated amination/[2,3]‐sigmatropic rearrangement of enantioenriched allylic selenides is expanded to provide access to the product classes listed in title.

2,3]-Sigmatropic Rearrangement of Allylic Selenimides: Strategy for the Synthesis of Peptides, Peptidomimetics, and N-Aryl Vinyl Glycines

The scope of the NCS-mediated amination/[2,3]-sigmatropic rearrangement of enantioenriched allylic selenides has been expanded to provide access to three new product classes. The use of N-protected amino acid amides provides a novel strategy for accessing peptide chains containing unnatural vinyl glycine amino acid residues. Also reported is the use of amino acid esters, allowing the diastereoselective synthesis of N,N-dicarboxymethylamines, a motif found in a number of pharmaceuticals. Furthermore, use of a range of N-aromatic and N-heteroaromatic amines allows the formation of enantioenriched N-arylamino acids, a motif found in a number of synthetically and biologically interesting compounds.

Fluxional Cyclic Seleninate Ester: NMR and Computational Studies, Glutathione Peroxidase-like Behavior, and Unexpected Rearrangement

The oxidation of allyl selenide 12 with hydrogen peroxide produced the corresponding allyl selenurane 14, the cyclic seleninate ester 4, or the rearranged O-allyl seleninate ester 18, dependng on the conditions. Crossover experiments with selenide 12 and its deuterated crotyl analogue 27 indicated an intramolecular rearrangement that proceeds by an intramolecular pathway where the allyl or crotyl group is translocated via its distal carbon atom to the hydroxymethyl functionality. Variable-temperature NMR experiments with cyclic seleninate ester 4 revealed fluxional behavior at room temperature that was catalyzed by trifluoroacetic acid. Computational studies indicated an activation energy of 12.3 kcal mol(-1) for hydroxyl interchange at selenium, comparable to the value of 15.5 kcal mol(-1) derived from the NMR experiments. The glutathione peroxidase-like activity of 4 was measured in an assay where the catalysis of the reduction of hydrogen peroxide with benzyl thiol was monitored by the appearance of dibenzyl disulfide. The catalytic activity of 4 was double that observed with the unsubstituted seleninate ester 2 but was limited by the competing accumulation of the relatively inert selenenyl sulfide 32, resulting in a deactivation pathway that competes with the primary catalytic cycle.

Synthesis and reactions of the optically active selenols derived from monoterpenes

A convenient methodology for the synthesis of optically active selenols, derived from p-menthane, carane, and pinane, is described. The selenols were oxidized with air to give the optically active diselenides, and were also converted into the corresponding allylic selenides via reaction with Z- and E-cinnamyl, geranyl, and neryl chlorides. Oxidation of the allylic selenides with mCPBA gave the optically active alcohols via [2,3]-sigmatropic rearrangement of the in situ generated allylic selenoxides.

ChemInform Abstract: Enantioselective Synthesis of α‐Alkyl, α‐Vinyl Amino Acids via [2,3]‐Sigmatropic Rearrangement of Selenimides.

Chiral α-alkyl,α-vinyl amino acids (quaternary vinyl glycine derivatives) are prepared with high levels of enantiomeric purity by [2,3]-sigmatropic rearrangement of allylic selenimides. The required trisubstituted allylic selenides are prepared by an organocatalytic α-selenenylation of aldehydes followed by Horner−Wadsworth−Emmons (HWE) olefination. Both (E)-and (Z)-geometrical isomers are available giving access to both enantiomers of the desired products.

Enantioselective Synthesis of α-Alkyl,α-Vinyl Amino Acids via [2,3]-Sigmatropic Rearrangement of Selenimides

Chiral α-alkyl,α-vinyl amino acids (quaternary vinyl glycine derivatives) are prepared with high levels of enantiomeric purity by [2,3]-sigmatropic rearrangement of allylic selenimides. The required trisubstituted allylic selenides are prepared by an organocatalytic α-selenenylation of aldehydes followed by Horner-Wadsworth-Emmons (HWE) olefination. Both (E)-and (Z)-geometrical isomers are available giving access to both enantiomers of the desired products.

Conjugate addition of vinylic organocuprates generated via transmetalation of phenylseleno‐substituted vinylzirconates: Functionalization at the 4‐position of enones

AbstractHydrozirconation of propargylic selenides (1) or 4‐phenylseleno‐1‐butyne (2) with Cp2ZrHCl, followed by in situ transmetalation to cuprate (Me2Cu(CN)Li2) and addition of enones, led to the formation of 1,4‐adducts in good yields. The adducts derived from 1 were subjected to oxidation with H2O2 to afford allylic alcohol derivatives via [2,3] sigmatropic rearrangement of allylic selenides. On the other hand, the oxidation of the products derived from 2 gave the corresponding ketones having a conjugated diene moiety at the β‐position via selenoxide elimination. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:545–552, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20720

Olefin Cross-Metathesis on Proteins: Investigation of Allylic Chalcogen Effects and Guiding Principles in Metathesis Partner Selection

Olefin metathesis has recently emerged as a viable reaction for chemical protein modification. The scope and limitations of olefin metathesis in bioconjugation, however, remain unclear. Herein we report an assessment of various factors that contribute to productive cross-metathesis on protein substrates. Sterics, substrate scope, and linker selection are all considered. It was discovered during this investigation that allyl chalcogenides generally enhance the rate of alkene metathesis reactions. Allyl selenides were found to be exceptionally reactive olefin metathesis substrates, enabling a broad range of protein modifications not previously possible. The principles considered in this report are important not only for expanding the repertoire of bioconjugation but also for the application of olefin metathesis in general synthetic endeavors.

ChemInform Abstract: Transition Metal Catalyzed Cleavage of Carbon—Selenium Bond and Addition to Alkynes and Allenes

AbstractReview: 75 refs.

ChemInform Abstract: A Novel Synthesis of Allyl Selenides by Reaction of an Organosamarium Reagent with Alkyl Selenocyanates.

Abstract Allyl samarium bromide is prepared by direct reaction of allyl bromide with samarium metal in the presence of a catalytic amount of iodine. This reacts with alkyl selenocyanates to give the corresponding allyl selenides in excellent yields under neutral and mild conditions.

Asymmetric, organocatalytic, three-step synthesis of alpha-hydroxy-(E)-beta,gamma-unsaturated esters.

An efficient and enantiocontrolled three-step synthesis of alpha-hydroxy-(E)-beta,gamma-unsaturated esters is reported. Enantioenriched alpha-selenyl aldehydes, prepared in one step by asymmetric, organocatalytic alpha-selenylation of aldehydes, were directly subjected to a Wittig reaction followed by allylic selenide to selenoxide oxidation and final spontaneous [2,3]-sigmatropic rearrangement to yield the target compounds in 43-65% overall yield and in 94-97% ee.

Transition-metal-catalyzed cleavage of carbon–selenium bond and addition to alkynes and allenes

This account summarizes our recent results on transition-metal-catalyzed cleavage of C–Se bond and addition to unsaturated hydrocarbons such as alkynes and allenes. Pd(0)-catalyzed intramolecular carbamoselenation of alkynes forms four- to eight-membered α-alkylidenelactams. Interestingly, four-membered ring formation is faster than five- and six-membered ring formation. Intramolecular vinylselenation of suitably structured alkynes offers pathways to conjugated δ-lactam frameworks. Electron-withdrawing groups on the vinyl moiety are essential to promote this reaction. Intermolecular 1,2-addition of selenol esters onto allenes proceeds with excellent regioselectivity and high stereoselectivity in the presence of a Pd(0) catalyst, producing functionalized allyl selenides. In addition, Pd(0)-catalyzed intramolecular selenocarbamoylation of allenes gives α,β-unsaturated γ- and δ-lactams with perfect regioselectivity. The scope and limitations, as well as reaction pathways, are discussed.

Palladium‐Catalyzed Intramolecular Selenocarbamoylation of Allenes with Carbamoselenoates: A New Entry to α,β‐Unsaturated Lactams

AbstractPd(PPh3)4‐catalyzed intramolecular selenocarbamoylation of allenes led to the regioselective formation of α,β‐unsaturated five‐ and six‐membered lactams having an allyl selenide unit. This procedure could be applied to the synthesis of the corresponding sulfur analogue by thiocarbamoylation as well as a cyclopentenone. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

ChemInform Abstract: Palladium‐Catalyzed Selenoacylation of Allenes Leading to the Regioselective Formation of Functionalized Allyl Selenides.

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