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Mari G, De Crescentini L, Favi G, Golobič A, Santeusanio S, Mantellini F. Useful Access to Uncommon Thiazolo[3,2- a]indoles. J Org Chem 2024; 89:1184-1192. [PMID: 38193441 PMCID: PMC10804410 DOI: 10.1021/acs.joc.3c02338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 12/21/2023] [Accepted: 12/26/2023] [Indexed: 01/10/2024]
Abstract
A practical and environmentally benign protocol for the assembly of poly substituted-thiazolo[3,2-a]indoles from 3-alkylated indoline-2-thiones and 2-halo-ketones has been developed. This metal-free approach consists in a complete chemo/regioselective formal [3 + 2] annulation that occurs in air, at 60 °C, and in water as the sole reaction medium. The opportunity to vary the substitution pattern up to six different positions, odorless manipulation of sulfurylated compounds, very easy product isolation, and mild reaction conditions are the main synthetic features of this method. The scaled-up experiment and the successive transformations of the products further demonstrate the utility of this chemistry.
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Affiliation(s)
- Giacomo Mari
- Department
of Biomolecular Sciences, Section of Chemistry and Pharmaceutical
Technologies, University of Urbino “Carlo
Bo”, Via I Maggetti
24, 61029 Urbino
(PU), Italy
| | - Lucia De Crescentini
- Department
of Biomolecular Sciences, Section of Chemistry and Pharmaceutical
Technologies, University of Urbino “Carlo
Bo”, Via I Maggetti
24, 61029 Urbino
(PU), Italy
| | - Gianfranco Favi
- Department
of Biomolecular Sciences, Section of Chemistry and Pharmaceutical
Technologies, University of Urbino “Carlo
Bo”, Via I Maggetti
24, 61029 Urbino
(PU), Italy
| | - Amalija Golobič
- Faculty
of Chemistry and Chemical Technology, University
of Ljubljana, Večna
pot 113, 1000 Ljubljana, Slovenia
| | - Stefania Santeusanio
- Department
of Biomolecular Sciences, Section of Chemistry and Pharmaceutical
Technologies, University of Urbino “Carlo
Bo”, Via I Maggetti
24, 61029 Urbino
(PU), Italy
| | - Fabio Mantellini
- Department
of Biomolecular Sciences, Section of Chemistry and Pharmaceutical
Technologies, University of Urbino “Carlo
Bo”, Via I Maggetti
24, 61029 Urbino
(PU), Italy
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2
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Mari G, De Crescentini L, Favi G, Santeusanio S, Mantellini F. Straightforward Access to Pyrazine‐(2,3)‐diones through Sequential Three‐Component Reaction. European J Org Chem 2023. [DOI: 10.1002/ejoc.202201080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Giacomo Mari
- Department of Biomolecular Sciences Section of Organic Chemistry and Pharmaceutical Technologies University of Urbino “Carlo Bo” Via I Maggetti 24 61029 Urbino PU Italy
| | - Lucia De Crescentini
- Department of Biomolecular Sciences Section of Organic Chemistry and Pharmaceutical Technologies University of Urbino “Carlo Bo” Via I Maggetti 24 61029 Urbino PU Italy
| | - Gianfranco Favi
- Department of Biomolecular Sciences Section of Organic Chemistry and Pharmaceutical Technologies University of Urbino “Carlo Bo” Via I Maggetti 24 61029 Urbino PU Italy
| | - Stefania Santeusanio
- Department of Biomolecular Sciences Section of Organic Chemistry and Pharmaceutical Technologies University of Urbino “Carlo Bo” Via I Maggetti 24 61029 Urbino PU Italy
| | - Fabio Mantellini
- Department of Biomolecular Sciences Section of Organic Chemistry and Pharmaceutical Technologies University of Urbino “Carlo Bo” Via I Maggetti 24 61029 Urbino PU Italy
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3
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Diaza-1,3-butadienes as Useful Intermediate in Heterocycles Synthesis. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27196708. [PMID: 36235245 PMCID: PMC9573662 DOI: 10.3390/molecules27196708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 07/26/2022] [Accepted: 07/26/2022] [Indexed: 11/05/2022]
Abstract
Many heterocyclic compounds can be synthetized using diaza-1,3-butadienes (DADs) as key structural precursors. Isolated and in situ diaza-1,3-butadienes, produced from their respective precursors (typically imines and hydrazones) under a variety of conditions, can both react with a wide range of substrates in many kinds of reactions. Most of these reactions discussed here include nucleophilic additions, Michael-type reactions, cycloadditions, Diels–Alder, inverse electron demand Diels–Alder, and aza-Diels–Alder reactions. This review focuses on the reports during the last 10 years employing 1,2-diaza-, 1,3-diaza-, 2,3-diaza-, and 1,4-diaza-1,3-butadienes as intermediates to synthesize heterocycles such as indole, pyrazole, 1,2,3-triazole, imidazoline, pyrimidinone, pyrazoline, -lactam, and imidazolidine, among others. Fused heterocycles, such as quinazoline, isoquinoline, and dihydroquinoxaline derivatives, are also included in the review.
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4
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Starosotnikov AM, Bastrakov MA. Heterocycles
via
Dearomatization Reactions. HETEROCYCLES 2022. [DOI: 10.1002/9783527832002.ch2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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5
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Diastereodivergent formal [4 + 1] cycloaddition of azoalkenes as one-carbon synthons. GREEN SYNTHESIS AND CATALYSIS 2022. [DOI: 10.1016/j.gresc.2022.05.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
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6
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Ghouse S, Sreenivasulu C, Kishore DR, Satyanarayana G. Recent developments by zinc based reagents/catalysts promoted organic transformations. Tetrahedron 2022. [DOI: 10.1016/j.tet.2021.132580] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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7
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Corrieri M, De Crescentini L, Mantellini F, Mari G, Santeusanio S, Favi G. Synthesis of Azacarbolines via PhIO 2-Promoted Intramolecular Oxidative Cyclization of α-Indolylhydrazones. J Org Chem 2021; 86:17918-17929. [PMID: 34871002 PMCID: PMC8689645 DOI: 10.1021/acs.joc.1c02217] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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An unprecedented
synthesis of polysubstituted indole-fused pyridazines
(azacarbolines) from α-indolylhydrazones under oxidative conditions
using a combination of iodylbenzene (PhIO2) and trifluoroacetic
acid (TFA) has been developed. This transformation is conducted without
the need for transition metals, harsh conditions, or an inert atmosphere.
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Affiliation(s)
- Matteo Corrieri
- Department of Biomolecular Sciences, Section of Chemistry and Pharmaceutical Technologies, University of Urbino "Carlo Bo", Via I Maggetti 24, 61029 Urbino, Italy
| | - Lucia De Crescentini
- Department of Biomolecular Sciences, Section of Chemistry and Pharmaceutical Technologies, University of Urbino "Carlo Bo", Via I Maggetti 24, 61029 Urbino, Italy
| | - Fabio Mantellini
- Department of Biomolecular Sciences, Section of Chemistry and Pharmaceutical Technologies, University of Urbino "Carlo Bo", Via I Maggetti 24, 61029 Urbino, Italy
| | - Giacomo Mari
- Department of Biomolecular Sciences, Section of Chemistry and Pharmaceutical Technologies, University of Urbino "Carlo Bo", Via I Maggetti 24, 61029 Urbino, Italy
| | - Stefania Santeusanio
- Department of Biomolecular Sciences, Section of Chemistry and Pharmaceutical Technologies, University of Urbino "Carlo Bo", Via I Maggetti 24, 61029 Urbino, Italy
| | - Gianfranco Favi
- Department of Biomolecular Sciences, Section of Chemistry and Pharmaceutical Technologies, University of Urbino "Carlo Bo", Via I Maggetti 24, 61029 Urbino, Italy
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8
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Crescentini LD, Favi G, Mari G, Ciancaleoni G, Costamagna M, Santeusanio S, Mantellini F. Experimental and Theoretical DFT Investigations in the [2,3]-Wittig-Type Rearrangement of Propargyl/Allyl-Oxy-Pyrazolones. Molecules 2021; 26:6557. [PMID: 34770965 PMCID: PMC8587800 DOI: 10.3390/molecules26216557] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 10/21/2021] [Accepted: 10/26/2021] [Indexed: 11/16/2022] Open
Abstract
Here we report the synthesis of interesting 3-alkyl-4-hydroxy-1-aryl-4-(propa-1,2-dienyl)1H-pyrazol-5(4H)-ones and 9-alkyl-7-aryl-1-oxa-7,8-diazaspiro[4.4]nona-3,8-dien-6-ones, starting from 1,2-diaza-1,3-dienes (DDs) and propargyl alcohol. The reaction proceeds through a sequence Michael-type nucleophilic attack/cyclization/[2,3]-Wittig rearrangement. In the same way, the reaction between the aforementioned DDs and allyl alcohol furnished 4-allyl-4-hydroxy-3-alkyl-1-aryl-1H-pyrazol-5(4H)-ones. A DFT study was also carried out, in order to have decisive clarifications about the mechanism.
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Affiliation(s)
- Lucia De Crescentini
- Department of Biomolecular Sciences, Section of Organic Chemistry and Organic Natural Compounds, University of Urbino “Carlo Bo”, Via I Maggetti 24, 61029 Urbino, PU, Italy; (G.F.); (G.M.); (S.S.)
| | - Gianfranco Favi
- Department of Biomolecular Sciences, Section of Organic Chemistry and Organic Natural Compounds, University of Urbino “Carlo Bo”, Via I Maggetti 24, 61029 Urbino, PU, Italy; (G.F.); (G.M.); (S.S.)
| | - Giacomo Mari
- Department of Biomolecular Sciences, Section of Organic Chemistry and Organic Natural Compounds, University of Urbino “Carlo Bo”, Via I Maggetti 24, 61029 Urbino, PU, Italy; (G.F.); (G.M.); (S.S.)
| | - Gianluca Ciancaleoni
- Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, PI, Italy; (G.C.); (M.C.)
| | - Marcello Costamagna
- Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, PI, Italy; (G.C.); (M.C.)
| | - Stefania Santeusanio
- Department of Biomolecular Sciences, Section of Organic Chemistry and Organic Natural Compounds, University of Urbino “Carlo Bo”, Via I Maggetti 24, 61029 Urbino, PU, Italy; (G.F.); (G.M.); (S.S.)
| | - Fabio Mantellini
- Department of Biomolecular Sciences, Section of Organic Chemistry and Organic Natural Compounds, University of Urbino “Carlo Bo”, Via I Maggetti 24, 61029 Urbino, PU, Italy; (G.F.); (G.M.); (S.S.)
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9
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Allred TK, Shaghafi MB, Chen PP, Tran Q, Houk KN, Overman LE. Constructing Saturated Guanidinum Heterocycles by Cycloaddition of N-Amidinyliminium Ions with Indoles. Org Lett 2021; 23:7618-7623. [PMID: 34546759 DOI: 10.1021/acs.orglett.1c02832] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
We report that structurally complex guanidinium heterocycles can be prepared in one step by regio- and stereoselective [4 + 2]-cycloadditions of N-amidinyliminium ions with indoles or benzothiophene. In contrast to reactions of these heterodienes with alkenes, density functional theory (DFT) calculations show that these cycloadditions take place in a concerted asynchronous fashion. The [4 + 2]-cycloaddition of N-amidinyliminium ions (1,3-diaza-1,3-dienes) with indoles and benzothiophene are distinctive, as related [4 + 2]-cycloadditions of N-acyliminium ions (1-oxa-3-aza-1,3-dienes) are apparently unknown.
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Affiliation(s)
- Tyler K Allred
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Michael B Shaghafi
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Pan-Pan Chen
- Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - Quan Tran
- Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - K N Houk
- Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - Larry E Overman
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
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10
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Li P, Yang F, Hu G, Zhang X. Palladium-Catalyzed One-Pot Synthesis of Pyrroloindolines from 2-Alkynyl Arylazides and Thioacetamides. J Org Chem 2021; 86:10360-10367. [PMID: 34281342 DOI: 10.1021/acs.joc.1c01058] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A novel and efficient synthetic method for the preparation of various pyrroloindolines from 2-alkynyl arylazides and thioacetamides was developed. The reaction was carried out in a one-pot process under mild reaction conditions to afford the products in moderate to good yields, which has the potential to be used in organic synthesis.
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Affiliation(s)
- Ping Li
- Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, People's Republic of China
| | - Fan Yang
- Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, People's Republic of China
| | - Guiwen Hu
- Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, People's Republic of China
| | - Xiaoxiang Zhang
- Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, People's Republic of China
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11
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Yao Z, Feng H, Xi H, Xi C, Liu W. CF 3SO 3H-enabled cascade ring-opening/dearomatization of indole derivatives to polycyclic heterocycles. Org Biomol Chem 2021; 19:4469-4473. [PMID: 33913995 DOI: 10.1039/d1ob00712b] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel dearomatization process to produce fused polycyclic indolines via a CF3SO3H-mediated cascade ring-opening of a β-lactam and hydroaminative cyclization is demonstrated. It provides a new strategy for the synthesis of important polycyclic indoline-2-amine derivatives in moderate to excellent yields, as well as with good functional group tolerance. Moreover, transformation of the product was performed to deliver the corresponding acid, alcohol and amide smoothly.
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Affiliation(s)
- Zhengdong Yao
- College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China.
| | - Huangdi Feng
- College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China.
| | - Hui Xi
- Key Laboratory of Tobacco Flavor Basic Research of CNTC, Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou 450001, China
| | - Chuanjun Xi
- College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China.
| | - Weiping Liu
- College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China.
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12
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Mlostoń G, Urbaniak K, Sobiecka M, Heimgartner H, Würthwein EU, Zimmer R, Lentz D, Reissig HU. Hetero-Diels-Alder Reactions of In Situ-Generated Azoalkenes with Thioketones; Experimental and Theoretical Studies. Molecules 2021; 26:2544. [PMID: 33925483 PMCID: PMC8123831 DOI: 10.3390/molecules26092544] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 04/20/2021] [Accepted: 04/22/2021] [Indexed: 11/18/2022] Open
Abstract
The hetero-Diels-Alder reactions of in situ-generated azoalkenes with thioketones were shown to offer a straightforward method for an efficient and regioselective synthesis of scarcely known N-substituted 1,3,4-thiadiazine derivatives. The scope of the method was fairly broad, allowing the use of a series of aryl-, ferrocenyl-, and alkyl-substituted thioketones. However, in the case of N-tosyl-substituted cycloadducts derived from 1-thioxo-2,2,4,4-tetramethylcyclobutan-3-one and the structurally analogous 1,3-dithione, a more complicated pathway was observed. By elimination of toluene sulfinic acid, the initially formed cycloadducts afforded 2H-1,3,4-thiadiazines as final products. Advanced DFT calculations revealed that the observed high regioselectivity was due to kinetic reaction control and that the (4 + 2)-cycloadditions of sterically less unhindered thiones occurred via highly unsymmetric transition states with shorter C..S-distances (2.27-2.58 Å) and longer N..C-distances (3.02-3.57 Å). In the extreme case of the sterically very hindered 2,2,4,4-tetramethylcyclobutan-1,3-dione-derived thioketones, a zwitterionic intermediate with a fully formed C‒S bond was detected, which underwent ring closure to the 1,3,4-thiadiazine derivative in a second step. For the hypothetical formation of the regioisomeric 1,2,3-thiadiazine derivatives, the DFT calculations proposed more symmetric transition states with considerably higher energies.
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Affiliation(s)
- Grzegorz Mlostoń
- Department of Organic and Applied Chemistry, Faculty of Chemistry, University of Lodz, 12 Tamka Street, 91-403 Lodz, Poland; (K.U.); (M.S.)
| | - Katarzyna Urbaniak
- Department of Organic and Applied Chemistry, Faculty of Chemistry, University of Lodz, 12 Tamka Street, 91-403 Lodz, Poland; (K.U.); (M.S.)
| | - Malwina Sobiecka
- Department of Organic and Applied Chemistry, Faculty of Chemistry, University of Lodz, 12 Tamka Street, 91-403 Lodz, Poland; (K.U.); (M.S.)
| | - Heinz Heimgartner
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland;
| | - Ernst-Ulrich Würthwein
- Organisch-Chemisches Institut and Center for Multiscale Theory and Computation (CMTC), Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
| | - Reinhold Zimmer
- Institut für Chemie und Biochemie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin, Germany; (R.Z.); (D.L.)
| | - Dieter Lentz
- Institut für Chemie und Biochemie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin, Germany; (R.Z.); (D.L.)
| | - Hans-Ulrich Reissig
- Institut für Chemie und Biochemie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin, Germany; (R.Z.); (D.L.)
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13
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Nishi T, Mishima N, Kato H, Yamada K. Syntheses of Heterocycle-2,3-Fused Indoline and Azaindoline Derivatives. Synlett 2021. [DOI: 10.1055/s-0037-1610771] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
AbstractWe describe a practical method for synthesizing heterocycle-2,3-fused indoline or azaindoline derivatives through haloetherification and cyclization. We applied this method in syntheses of six- to eight-membered heterocycle-2,3-fused indoline and azaindoline derivatives. These derivatives, which contain sp3-hybridized carbons, might be useful as new scaffolds in medicinal chemistry.
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14
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Duan SB, Zhang HY, Hao BY, Zhao J, Han YP, Zhang Y, Liang YM. Palladium-catalyzed intramolecular diastereoselective dearomatization reaction of indoles with N-tosylhydrazones. Org Chem Front 2021. [DOI: 10.1039/d1qo00893e] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A novel, highly diastereoselective palladium-catalyzed dearomative reaction of N-halobenzoyl o-haloaniline derivatives has been developed using functionalized N-tosylhydrazones as the coupling partners.
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Affiliation(s)
- Shao-Bo Duan
- School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, People's Republic of China
| | - Hong-Yu Zhang
- School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, People's Republic of China
| | - Bo-Ya Hao
- School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, People's Republic of China
| | - Jiquan Zhao
- School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, People's Republic of China
| | - Ya-Ping Han
- School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, People's Republic of China
| | - Yuecheng Zhang
- School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, People's Republic of China
| | - Yong-Min Liang
- State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, People's Republic of China
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15
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Ciccolini C, De Crescentini L, Mantellini F, Mari G, Santeusanio S, Favi G. Construction of Unusual Indole-Based Heterocycles from Tetrahydro-1 H-pyridazino[3,4- b]indoles. Molecules 2020; 25:molecules25184124. [PMID: 32916997 PMCID: PMC7571100 DOI: 10.3390/molecules25184124] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 09/04/2020] [Accepted: 09/07/2020] [Indexed: 11/21/2022] Open
Abstract
Herein, we report the successful syntheses of scarcely represented indole-based heterocycles which have a structural connection with biologically active natural-like molecules. The selective oxidation of indoline nucleus to indole, hydrolysis of ester and carbamoyl residues followed by decarboxylation with concomitant aromatization of the pyridazine ring starting from tetrahydro-1H-pyridazino[3,4-b]indole derivatives lead to fused indole-pyridazine compounds. On the other hand, non-fused indole-pyrazol-5-one scaffolds are easily prepared by subjecting the same C2,C3-fused indoline tetrahydropyridazines to treatment with trifluoroacetic acid (TFA). These methods feature mild conditions, easy operation, high yields in most cases avoiding the chromatographic purification, and broad substrate scope. Interestingly, the formation of indole linked pyrazol-5-one system serves as a good example of the application of the umpolung strategy in the synthesis of C3-alkylated indoles.
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