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Harold W. Moore - One of the best experts on this subject based on the ideXlab platform.
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Rearrangements of Cyclobutenones. Synthesis of N‐Methyl‐7,8‐dihydrobenzophenanthridine‐9,12‐diols and Related Compounds.
ChemInform, 2010Co-Authors: Antonio R. Hergueta, Harold W. MooreAbstract:A useful synthetic route to benzophenanthridines and annulated derivatives is reported. These arise from the thermolysis (refluxing chlorobenzene) of squaric acid-derived 4-(3-N-methyl-N-arylpropynyl)-Cyclobutenones via a mechanism which involves an electrocyclic ring opening of the Cyclobutenone to the corresponding enynylketenes. Subsequent ring closure to a diradical intermediate followed by radical arylation gives the benzophenanthridines.
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Rearrangements of Cyclobutenones. Electrocyclic ring closure and thermal ring expansions of 3-allenyl- and 3-alkynyl-2-dienyl-4,4-dimethoxyCyclobutenones.
The Journal of organic chemistry, 2002Co-Authors: Antonio R. Hergueta, Harold W. MooreAbstract:Thermal rearrangements of 2-allenyl- and 2-alkynyl-3-(2-ethenylphenyl)-4,4-dimethoxyCyclobutenones were studied. At ambient temperature, the allenyl compounds undergo an electrocyclic cascade to give bicyclo[4.2.0]octadienyl-fused Cyclobutenones. These unusual tetracyclic Cyclobutenones were shown to be viable synthetic precursors to benzo[a]anthracene-7,12-diones, compounds representing the framework of the angucycline group of naturally occurring antibiotics. In contrast, the 2-alkynylCyclobutenones are stable at ambient temperature but undergo a facile rearrangement at 110 degrees C (toluene) to give the previously unknown naphthalene derivatives, 1,2-dihydro-2,2-dimethoxy-1-(3-alkenylidene)naphtho[2,1-b]furans.
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Cyclobutenone ethylenedithioacetals and their ready electrocyclic ring opening
Synthesis, 2001Co-Authors: Wilko Regenhardt, Ernst Schaumann, Harold W. MooreAbstract:PAPER Cyclobutenone Ethylenedithioacetals and Their Ready Electrocyclic Ring Opening a Synthesi and Subsequent Ring Openi g of Cyclobutenone Ethylen d Regenhardt, Wilko ithioacetals Ernst Schaumann,* a Harold W. Moore* b a Institut fur Organische Chemie, Technische Universitat Clausthal, Leibnizstrase 6, 38678 Clausthal-Zellerfeld, Germany Fax +49(5323)722858; E-mail: ernst.schaumann@tu-clausthal.de b Department of Chemistry, University of California-Irvine, Irvine, CA 92697–2025, USA Fax +1(949)8242210; E-mail: halmoore@uci.edu Received 5 February 2001; revised 12 March 2001 Key words: Cyclobutenones, dithioacetals, transthioacetalization, electrocyclic ring opening, Diels - Alder reaction Cyclobutenone derivatives have been efficiently used for the synthesis of highly substituted p-quinones and related annulated compounds over the last 15 years. 1–3 The ther- mal ring expansion is presumed to proceed via ring open- ing of the Cyclobutenone to a vinyl ketene intermediate which then undergoes elecrocyclic ring closure to form the six-membered ring. Starting materials of particular note are cyclobutenedione monoketals. Such compounds having predictable regiochemistry are readily prepared and serve as useful precursors to asymmetrically substi- tuted p-quinones. 4,5 Our interest in organosulfur derivatives of Cyclobutenones 6 led us to investigate the chemistry of cy- clobutenone dithioacetals. In particular, we were interest- ed in 1,3-dithiolane derivatives because of their potential utility for the generation of cyclobutenediones via a base induced [3 + 2] cycloreversion reaction. 7 Reported herein is an efficient preparation of cy- clobutenedione monodithioacetals involving the tran- sthioacetalization of the corresponding dialkyl acetals. Firouzabadi and Iranpoor 8 have developed a method for a selective transthioacetalization of open chain acetals in the presence of cyclic acetals by the use of catalytic amounts of ZrCl 4 . This methodology could be extended to the transthioacetalization of cyclobutenedione monoace- tals. Thus, the readily available dimethyl acetals 1 were converted to the corresponding 1,3-dithiolanes 2 in the presence of 1,2-ethanedithiol (1.05 equivalents) and ZrCl 4 (15 mol%) in very good yields and with complete control of chemoselectivity (Scheme 1). R 2 SH, HS ZrCl 4 , CH 2 Cl 2 OMe OMe R 1 O S R 1 O Scheme 1 Bisthioacetalization or other by-products were not ob- served for any of the examples listed above. It is noted that even a vinylic methoxy group was tolerated under these conditions (Table 1). Table 1 Transthioacetalization with ZrCl 4 Product R 1 R 2 Yield Mp (° C) 2a Bu Me oil 2b t-Bu Me 2c Ph Me 2d t-Bu vinyl oil 2e Bu OMe oil 2f t-Bu OMe 2g Ph OMe 2h C o C-Bu OMe oil The symmetrically substituted cyclobutenedione monoet- hylendithioacetal 2i was prepared by a BF 3 × OEt 2 cata- lyzed thioacetalization of 3,4-dimethylcyclobutenedione (3) (Scheme 2). The degree of the accompanying bisthio- acetalation was reduced by a very slow addition of a CH 2 Cl 2 solution of ethanedithiol and BF 3 × OEt 2 to a solu- tion of the dione in CH 2 Cl 2 at 0°C. However, under these conditions, we obtained 8% of the bisthioacetal 4 and 73% of the desired monoethylenedithioacetal 2i. O HS Synthesis 2001, No. 7, 01 06 2001. Article Identifier: 1437-210X,E;2001,0,07,1076,1080,ftx,en;E01401SS.pdf. © Georg Thieme Verlag Stuttgart · New York ISSN 0039-7881 S R 2 O SH S BF 3 OEt 2 , CH 2 Cl 2 S S O 2i Scheme 2 S S S Downloaded by: IP-Proxy University of California Irvine, University of California. Copyrighted material. Abstract: Reported here is a general regiospecific synthesis of cy- clobutenedione monoethylendithioacetals which readily undergo ring opening after addition of an organolithium reagent. The gener- ated acyclic enols either tautomerize to the corresponding carbonyl compounds or can be trapped as silylenol ethers, which serve as electron rich dienes in Diels - Alder additions with tetracyanoethyl- ene or maleic anhydride.
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Rearrangements of Cyclobutenones. Synthesis of N-Methyl-7,8-dihydrobenzophenanthridine-9,12-diols and Related Compounds
The Journal of Organic Chemistry, 1999Co-Authors: Antonio R. Hergueta, Harold W. MooreAbstract:A useful synthetic route to benzophenanthridines and annulated derivatives is reported. These arise from the thermolysis (refluxing chlorobenzene) of squaric acid-derived 4-(3-N-methyl-N-arylpropynyl)-Cyclobutenones via a mechanism which involves an electrocyclic ring opening of the Cyclobutenone to the corresponding enynylketenes. Subsequent ring closure to a diradical intermediate followed by radical arylation gives the benzophenanthridines.
Mingsheng Tang - One of the best experts on this subject based on the ideXlab platform.
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a computational study on the n heterocyclic carbene catalyzed csp2 csp3 bond activation 4 2 cycloaddition cascade reaction of Cyclobutenones with imines a new application of the conservation principle of molecular orbital symmetry
Physical Chemistry Chemical Physics, 2016Co-Authors: Yang Wang, Haoyang Zhang, Donghui Wei, Mingsheng TangAbstract:A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp2–Csp3 single bond activation of Cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to Cyclobutenone, C–C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the CN bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the CO bond to a dienolate intermediate. Moreover, the Re face addition of the CN bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C–C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction.
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A computational study on the N-heterocyclic carbene-catalyzed Csp2–Csp3 bond activation/[4+2] cycloaddition cascade reaction of Cyclobutenones with imines: a new application of the conservation principle of molecular orbital symmetry
Physical chemistry chemical physics : PCCP, 2016Co-Authors: Yang Wang, Haoyang Zhang, Donghui Wei, Mingsheng TangAbstract:A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp2–Csp3 single bond activation of Cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to Cyclobutenone, C–C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the CN bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the CO bond to a dienolate intermediate. Moreover, the Re face addition of the CN bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C–C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction.
Lanny S. Liebeskind - One of the best experts on this subject based on the ideXlab platform.
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A Synthesis of Substituted 2‐Pyrones by Carbonylative Cross‐Coupling Thermolysis of 4‐HaloCyclobutenones with Alkenyl‐, Aryl‐, and Heteroarylstannanes.
ChemInform, 2010Co-Authors: Lanny S. Liebeskind, Jeng Han WangAbstract:Abstract Palladium catalyzed carbonylative cross-coupling of 4-chloro-2,3-disubstituted-2-Cyclobutenones with alkenyl-, aryl-, and heteroaryltin reagents and thermolysis provides a general method for the synthesis of 2,3,6-trisubstituted-2-pyrones. The reaction is regiospecific, coupling occurring preferentially at the 4-position of the Cyclobutenone.
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The regiospecific synthesis of angularly-fused xanthones via the benzannulation of 1,2-adducts derived from 3-(o-anisoyl)-4-substituted cyclobutenediones and their dithianyl derivatives
Tetrahedron Letters, 1997Co-Authors: L. Sun, Lanny S. LiebeskindAbstract:Abstract Described in this paper is a new synthetic approach to angularly-fused and simpler substituted xanthones that is based upon the benzannulation of 2-(o-anisoyl)-4-heteroaryl-2-Cyclobutenones and 2-(2-(o-anisyl)-1,3-dithian-2-yl)-4-alkenyl-2-Cyclobutenones followed by facile intramolecular loss of methanol and cyclization to the xanthone.
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benzannulation of aromatic heterocycles a regiocontrolled method for construction of substituted benzo and dibenzofurans and benzo and dibenzothiophenes
Journal of Organic Chemistry, 1993Co-Authors: Lanny S. Liebeskind, Jeng Han WangAbstract:4-Chloro-2,3-disubstituted-2-Cyclobutenones undergo palladium-catalyzed cross-coupling with oxygen and sulfur heteroaryl tin reagents, and upon thermolysis at 100 o C, good to high yields of substituted benzannulated heteroaromatics are formed. Relying on the control inherent in the construction of 4-chloro-2,3-disubstituted-2-Cyclobutenones, regioisomeric substituted heteroaromatics are easily prepared
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A synthesis of substituted 2-pyrones by carbonylative cross-coupling-thermolysis of 4-haloCyclobutenones with alkenyl-, aryl-, and heteroarylstannanes
Tetrahedron, 1993Co-Authors: Lanny S. Liebeskind, Jeng Han WangAbstract:Abstract Palladium catalyzed carbonylative cross-coupling of 4-chloro-2,3-disubstituted-2-Cyclobutenones with alkenyl-, aryl-, and heteroaryltin reagents and thermolysis provides a general method for the synthesis of 2,3,6-trisubstituted-2-pyrones. The reaction is regiospecific, coupling occurring preferentially at the 4-position of the Cyclobutenone.
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A synthesis of highly substituted aromatics through regiocontrolled construction of Cyclobutenones bearing unsaturated substituents at the 4-position
Journal of the American Chemical Society, 1992Co-Authors: Damian J. Krysan, Angela Gurski, Lanny S. LiebeskindAbstract:2,3-Substituted 4-chloro-2-Cyclobutenones, prepared by regiospecific transformations of substituted cyclobutenediones, undergo palladium-catalyzed cross-coupling with vinyl- and arylstannanes and vinylzirconium reagents to form 4-R unsat -2-Cyclobutenones. On thermolysis (100 o C), these substrates transform into substituted phenols in high yield. A pentasubstituted aromatic and a variety of tri- and tetrasubstituted aromatic compounds were prepared in a regiospecific fashion using this chemistry
Samuel J. Danishefsky - One of the best experts on this subject based on the ideXlab platform.
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Organic Syntheses - Preparation of Cyclobutenone
Organic Syntheses, 2014Co-Authors: Audrey G. Ross, Samuel J. DanishefskyAbstract:3-Oxocyclobutanecarboxylic acid Mercury (II) oxide red Bromine 3-Bromocyclobutanone Tri-n-butylamine Cyclobutenone Deuterated chloroform Keywords: Cyclobutenone; Toxicity; Storage; Diels-Alder reactions; Safety; Waste disposal
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preparation of Cyclobutenone
Organic Syntheses, 2014Co-Authors: Audrey G. Ross, Samuel J. DanishefskyAbstract:3-Oxocyclobutanecarboxylic acid Mercury (II) oxide red Bromine 3-Bromocyclobutanone Tri-n-butylamine Cyclobutenone Deuterated chloroform Keywords: Cyclobutenone; Toxicity; Storage; Diels-Alder reactions; Safety; Waste disposal
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Intramolecular Diels–Alder Reactions of Cycloalkenones: Translation of High Endo Selectivity to Trans Junctions
2012Co-Authors: Audrey G. Ross, Samuel J. DanishefskyAbstract:Intramolecular Diels–Alder reactions of Cyclobutenone and larger cycloalkenones are described. High levels of endo addition attained from Lewis acid catalysis translate to trans hydrindene junctions upon fragmentation of the tricyclic adducts
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Cyclobutenone as a highly reactive dienophile expanding upon diels alder paradigms
ChemInform, 2010Co-Authors: Samuel J. DanishefskyAbstract:Cyclobutenone was employed as a dienophile in Diels−Alder cycloadditions, provide diverse and complex cycloadducts in good yields. Experimental outcomes indicated Cyclobutenone to be more reactive than either cyclopentenone or cyclohexenone. In addition, cycloadducts bearing a strained cyclobutanone moiety were able to undergo regioselective ring expansions to produce corresponding cyclopentanones, lactones, and lactams, which are otherwise difficultly obtained by direct Diels−Alder reactions.
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Cyclobutenone as a Highly Reactive Dienophile: Expanding Upon Diels—Alder Paradigms.
ChemInform, 2010Co-Authors: Samuel J. DanishefskyAbstract:Cyclobutenone was employed as a dienophile in Diels−Alder cycloadditions, provide diverse and complex cycloadducts in good yields. Experimental outcomes indicated Cyclobutenone to be more reactive than either cyclopentenone or cyclohexenone. In addition, cycloadducts bearing a strained cyclobutanone moiety were able to undergo regioselective ring expansions to produce corresponding cyclopentanones, lactones, and lactams, which are otherwise difficultly obtained by direct Diels−Alder reactions.
Yang Wang - One of the best experts on this subject based on the ideXlab platform.
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a computational study on the n heterocyclic carbene catalyzed csp2 csp3 bond activation 4 2 cycloaddition cascade reaction of Cyclobutenones with imines a new application of the conservation principle of molecular orbital symmetry
Physical Chemistry Chemical Physics, 2016Co-Authors: Yang Wang, Haoyang Zhang, Donghui Wei, Mingsheng TangAbstract:A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp2–Csp3 single bond activation of Cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to Cyclobutenone, C–C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the CN bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the CO bond to a dienolate intermediate. Moreover, the Re face addition of the CN bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C–C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction.
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A computational study on the N-heterocyclic carbene-catalyzed Csp2–Csp3 bond activation/[4+2] cycloaddition cascade reaction of Cyclobutenones with imines: a new application of the conservation principle of molecular orbital symmetry
Physical chemistry chemical physics : PCCP, 2016Co-Authors: Yang Wang, Haoyang Zhang, Donghui Wei, Mingsheng TangAbstract:A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp2–Csp3 single bond activation of Cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to Cyclobutenone, C–C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the CN bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the CO bond to a dienolate intermediate. Moreover, the Re face addition of the CN bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C–C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction.
