- Phosphetane oxides as redox cycling catalysts in the catalytic wittig reaction at room temperature
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Recently, phosphorus redox cycling has gained significant importance for a number of transformations originally requiring the use of stoichiometric amounts of phosphorus reagents. While these methodologies have several benefits, high catalyst loadings (≥10 mol percent) and harsh reaction conditions (T ≥ 100 °C) often limit their versatility and applicability. Herein, we report differently substituted phosphetane oxides as efficient catalysts for the catalytic Wittig reaction. The phosphetane scaffold is easy to modify, and a number of catalysts can be obtained in a simple two-step synthesis. The activity in the Wittig reaction significantly surpasses previously reported phospholane-based catalysts and the reaction can be conducted with catalyst loadings as low as 1.0 mol percent even at room temperature. Furthermore, a Br?nsted acid additive is no longer required to achieve high yields at these mild conditions. A methyl-substituted phosphetane oxide was employed to synthesize 25 different alkenes with yields of up to 97percent. The methodology has a good functional group tolerance and the reaction can be performed starting with alkyl chlorides, bromides, or iodides. Additionally, it was possible to use poly(methylhydrosiloxane) as the terminal reductant in the catalytic Wittig reaction employing 2-MeTHF as a renewable solvent. The intermediates of the Wittig reaction were analyzed by 31P NMR spectroscopy, and in situ NMR experiments confirmed phosphane oxide as the resting state of the catalyst. Further kinetic investigations revealed a striking influence of the base on the rate of phosphane oxide reduction.
- Longwitz, Lars,Spannenberg, Anke,Werner, Thomas
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p. 9237 - 9244
(2019/10/08)
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- Copper-catalyzed vinylogous aerobic oxidation of unsaturated compounds with air
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A mild and operationally simple copper-catalyzed vinylogous aerobic oxidation of β,γ- and α,β-unsaturated esters is described. This method features good yields, broad substrate scope, excellent chemo- and regioselectivity, and good functional group tolerance. This method is additionally capable of oxidizing β,γ- and α,β-unsaturated aldehydes, ketones, amides, nitriles, and sulfones. Furthermore, the present catalytic system is suitable for bisvinylogous and trisvinylogous oxidation. Tetramethylguanidine (TMG) was found to be crucial in its role as a base, but we also speculate that it serves as a ligand to copper(II) triflate to produce the active copper(II) catalyst. Mechanistic experiments conducted suggest a plausible reaction pathway via an allylcopper(II) species. Finally, the breadth of scope and power of this methodology are demonstrated through its application to complex natural product substrates.
- Zhang, Hai-Jun,Schuppe, Alexander W.,Pan, Shi-Tao,Chen, Jin-Xiang,Wang, Bo-Ran,Newhouse, Timothy R.,Yin, Liang
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supporting information
p. 5300 - 5310
(2018/04/24)
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- Stereoselective Organocatalytic Synthesis of α,α-Difluoro-γ,γ-Disubstituted Butenals
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A highly stereoselective reaction of α,α-difluoro-γ,γ-disubstituted butenals 2 bearing two different substituents at the γ position has been developed with an organocatalytic system of l-proline (30 mol %) and salicylic acid (60 mol %). This novel reactio
- Arimitsu, Satoru,Nakasone, Makoto
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p. 6707 - 6713
(2016/08/16)
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- Enantioselective α-and γ-alkylation of α,β- unsaturated aldehydes using dienamine activation
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The enantioselective alkylation of α,β-unsaturated aldehydes with stabilized carbocations as electrophiles via the activation as dienamine intermediates is described. This unique application of dienamine catalysis allows for the first enantioselective γ-a
- Stiller, Julian,Marques-Lopez, Eugenia,Herrera, Raquel P.,Froehlich, Roland,Strohmann, Carsten,Christmann, Mathias
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supporting information; experimental part
p. 70 - 73
(2011/03/22)
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- Stereoselective olefination reactions promoted by Rieke manganese
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A study of the advantages of using manganese, an inexpensive and nontoxic metal, to perform stereoselective β-elimination reactions and to promote sequential olefination reactions of aldehydes to obtain α,β- unsaturated esters and amides is presented. Various elimination reactions, all of them characterized by occurring with complete stereoselectivity and in high yields, were performed using active manganese (Mn*) as metalating agent. This ability of manganese has been applied to develop a novel and direct synthesis of (E)-α,β-unsaturated esters or amides and (Z)-α,β-unsaturated α-halo esters and α-choroamides through a Mn*-mediated sequential olefination protocol of aldehydes with dichloro esters or amides and trihalo esters or trichloroamides, respectively. Georg Thieme Verlag Stuttgart.
- Concellon, Jose M.,Rodriguez-Solla, Humberto,Del Amo, Vicente,Diaz, Pamela
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experimental part
p. 2634 - 2645
(2009/12/06)
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- Highly (E)-selective wadsworth-emmons reactions promoted by methylmagnesium bromide
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(Chemical Equation Presented) An experimentally simple protocol for the very highly (E)-selective Wadsworth-Emmons reaction [(E):(Z) selectivities in excess of 180:1 in some cases] of a range of straight-chain and branched aliphatic, substituted aromatic, and base-sensitive aldehydes via reaction with an alkyl diethylphosphonoacetate and MeMgBr is reported.
- Claridge, Timothy D. W.,Davies, Stephen G.,Lee, James A.,Nicholson, Rebecca L.,Roberts, Paul M.,Russell, Angela J.,Smith, Andrew D.,Toms, Steven M.
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supporting information; experimental part
p. 5437 - 5440
(2009/06/18)
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- The first sequential reaction promoted by manganese: Complete stereoselective synthesis of (E)-α,β-unsaturated esters from 2,2-dichloroesters and aldehydes
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(Chemical Equation Presented) α,β-Unsaturated esters were obtained with complete control of stereoselectivity utilizing a sequential reaction of dichloroesters with a variety of aldehydes, promoted by active manganese. This methodology is generally applicable, and the C-C double bond can be di- or trisubstituted. A mechanism based on a successive aldol-type reaction/β-elimination is proposed to explain these results.
- Concellon, Jose M.,Rodriguez-Solla, Humberto,Diaz, Pamela,Llavona, Ricardo
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p. 4396 - 4400
(2008/02/05)
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- An efficient synthesis of (E)-α,β-unsaturated ketones and esters with total stereoselectivity by using chromium dichloride
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(E)-α,β-Unsaturated ketones 1 or esters 2 can be obtained with complete stereoselectivity by reaction of different 2-chloro-3-hydroxy ketones 3 or esters 4 and CrCl2. A comparative study of the results of synthesis of ketones 1 with CrCl2 or samarium is performed. A mechanism to explain both β-elimination reactions has been proposed.
- Concellón, José M.,Rodríguez-Solla, Humberto,Méjica, Carmen
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p. 3292 - 3300
(2007/10/03)
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- A highly stereospecific synthesis of (E)-α,β-unsaturated esters
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CrCl2-induced olefination of aldehydes using methyl dichloroacetate exclusively generates (E)-α,β-unsaturated esters in excellent yields. The intermediate α-chloro-β-hydroxy adducts could also be isolated in good yields under conditions of limited reagent.
- Barma, Deb K.,Kundu, Asish,Bandyopadhyay, Anish,Kundu, Abhijit,Sangras, Bhavani,Briot, Anne,Mioskowski, Charles,Falck
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p. 5917 - 5920
(2007/10/03)
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- Synthesis of (E)-α,β-unsaturated esters with total diastereoselectivity by using chromium dichloride
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Synthesis of di- and trisubstituted (E)-α,β-unsaturated esters is easily achieved by using chromium dichloride through an elimination reaction of a diastereoisomeric mixture of α-halo-β-hydroxy esters. The starting materials were easily prepared by the aldol reaction of lithium enolates of α-chloroesters with aldehydes. A mechanism to explain this elimination process is proposed.
- Concellón, José M.,Rodríguez-Solla, Humberto,Méjica, Carmen
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p. 2977 - 2979
(2007/10/03)
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- Synthesis of (E)-α,β-unsaturated esters with total or high diastereoselectivity from α,β-epoxyesters
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Chemical equation presented High stereoselective β-elimination in 2,3-epoxyesters 1 was achieved using samarium diiodide, yielding α,β-unsaturated esters 2, in which the C=C bond is di-, tri- or tetrasubstituted. The starting compounds 1 are easily prepared by reaction of the corresponding lithium enolates of a-chloroesters with aldehydes or ketones at -78 °C. The influence of the reaction conditions and the structure of the starting compounds in the stereoselectivity of the β-elimination reaction is also discussed.
- Concellon, Jose M.,Bardales, Eva
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p. 189 - 191
(2007/10/03)
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- STEREOSPECIFIC CROSS-COUPLING REACTIONS OF 3-ARYLSULFINYLPROPENOATES WITH ORGANOMETALLIC REAGENTS
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(E)- or (Z)-3-arylsulfinylpropenoates have been reacted with several organometallic reagents.Grignard reagents were found to promote only the complete substitution of the arylsulfinyl group in good yields (up to 92percent).The reaction followed a stereochemical course of retention of configuration with high values of stereospecificity (up to 99percent) in most cases.The observation made are discussed in the light of current views concerning nucleophilic substitution at a vinyl carbon atom.The addition-elimination pathway is considered valid, whereas a route involving the formation of a sulfurane as an intermediate, followed by a ligand coupling, is considered less likely.
- Cardellicchio, Cosimo,Cicciomessere, Angela Rosa,Naso, Francesco,Tortorella, Paolo
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p. 555 - 558
(2007/10/03)
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- Carbonyl olefination with α-stannyl ester enolates: a new synthesis of α,β-unsaturated esters
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The reaction of α-stannyl ester enolates with carbonyl compounds is described. α,β-Unsaturated esters are obtained in good yields.A reaction mechanism is proposed.
- Zapata, Antonio,Nunez, Beatriz M.,Ferrer, Fernando J.
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- Reactions of N-Sulfinyl Compounds, XV. - Synthesis of 2-Alkenesulfinic Acid Amides - Structure-Reactivity Relationships for N-Sulfinyl Compounds as Enophiles
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The reactivity of N-sulfinyl compounds R6NSO 2 in ene-reactions shows a large variation depending on the nature of the group R6.Haloalkanesulfonamide derivatives react even with very unreactive alkenes.The scope of this method for the synthesis of sulfinic acid amides and the side reactions are discussed.
- Bussas, Reinhard,Kresze, Guenter
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p. 545 - 563
(2007/10/02)
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