- Asymmetric oxidative coupling of hydroxycarbazoles: Facile synthesis of (+)-bi-2-hydroxy-3-methylcarbazole
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Asymmetric oxidative coupling reactions of hydroxycarbazoles have been established using a chiral dinuclear vanadium complex. To demonstrate the utility of vanadium-catalyzed reactions, we have used them to synthesize (+)-bi-2-hydroxy-3-carbazole in three steps from cyclohexanone and commercially available aniline derivatives.
- Sako, Makoto,Sugizaki, Akimasa,Takizawa, Shinobu
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p. 2751 - 2753
(2018/03/05)
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- Divergent and Orthogonal Approach to Carbazoles and Pyridoindoles from Oxindoles via Indole Intermediates
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The previously unexplored Grignard addition to oxindoles provides a regiospecific approach to 2- and 2,3-disubstituted indole derivatives in high yields via a one-pot aromatization driven dehydration pathway. This method allows a convenient preparation of diallyl indoles that are used as ring-closing metathesis (RCM) precursors for the orthogonal synthesis of pyrido[1,2-a]indoles and carbazoles. The synthetic utility of this method is illustrated by the synthesis of a microtubulin inhibitor and naturally occurring carbazole alkaloids.
- Mandal, Tirtha,Chakraborti, Gargi,Karmakar, Shilpi,Dash, Jyotirmayee
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p. 4759 - 4763
(2018/08/24)
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- Pyrano[3,2-a]carbazole alkaloids as effective agents against ischemic stroke in vitro and in vivo
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A series of pyrano[3,2-a]carbazole alkaloids were designed and synthesized as analogues of Claulansine F (Clau F, 10a) isolated from Clausena lansium. Some of compounds showed strong neuroprotective effects and were promising agents against ischemic stroke. Among these compounds, 7c was the most active in inhibiting the programmed death of PC12 cells and primary cortical neurons. This compound induced neuroprotection following ischemic reperfusion and decreased neurological deficit scores in treated animals. Furthermore, 7c could penetrate the blood-brain barrier (BBB) in rats, and its exposure in the brain was 4.3-fold higher than that in plasma. More importantly, compared to edaravone, 7c exhibited stronger free radical scavenging activity. Our findings suggest that 7c may be promising for further evaluation as an intervention for ischemic stroke.
- Zang, Yingda,Song, Xiuyun,Li, Chuangjun,Ma, Jie,Chu, Shifeng,Liu, Dandan,Ren, Qian,Li, Yan,Chen, Naihong,Zhang, Dongming
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p. 438 - 448
(2017/12/07)
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- Enantioselective Vanadium-Catalyzed Oxidative Coupling: Development and Mechanistic Insights
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The evolution of a more reactive chiral vanadium catalyst for enantioselective oxidative coupling of phenols is reported, ultimately resulting in a simple monomeric vanadium species combined with a Br?nsted or Lewis acid additive. The resultant vanadium complex is found to effect the asymmetric oxidative ortho-ortho coupling of simple phenols and 2-hydroxycarbazoles with good to excellent levels of enantioselectivity. Experimental and quantum mechanical studies of the mechanism indicate that the additives aggregate the vanadium monomers. In addition, a singlet to triplet crossover is implicated prior to carbon-carbon bond formation. The two lowest energy diastereomeric transition states leading to the enantiomeric products differ substantially with the path to the minor enantiomer involving greater torsional strain between the two phenol moieties.
- Kang, Houng,Herling, Madison R.,Niederer, Kyle A.,Lee, Young Eun,Vasu Govardhana Reddy, Peddiahgari,Dey, Sangeeta,Allen, Scott E.,Sung, Paul,Hewitt, Kirsten,Torruellas, Carilyn,Kim, Gina J.,Kozlowski, Marisa C.
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p. 14362 - 14384
(2018/11/23)
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- Asymmetric Oxidative Coupling of Phenols and Hydroxycarbazoles
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The first examples of asymmetric oxidative coupling of simple phenols and 2-hydroxycarbazoles are outlined. Generation of a more vanadium catalyst by ligand design and by addition of an exogenous Br?nsted or Lewis acid was found to be key to coupling the more oxidatively resistant phenols. The resultant vanadium complex is both more Lewis acidic and more strongly oxidizing. Good to excellent levels of enantioselectivity could be obtained, and simple trituration readily provided the products with ≥95% ee.
- Kang, Houng,Lee, Young Eun,Reddy, Peddiahgari Vasu Govardhana,Dey, Sangeeta,Allen, Scott E.,Niederer, Kyle A.,Sung, Paul,Hewitt, Kirsten,Torruellas, Carilyn,Herling, Madison R.,Kozlowski, Marisa C.
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p. 5505 - 5508
(2017/10/25)
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- Synthesis of Carbazoles and Carbazole-Containing Heterocycles via Rhodium-Catalyzed Tandem Carbonylative Benzannulations
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Polycyclic aromatic compounds are important constituents of pharmaceuticals and other materials. We have developed a series of Rh-catalyzed tandem carbonylative benzannulations for the synthesis of tri-, tetra-, and pentacyclic heterocycles from different types of aryl propargylic alcohols. These tandem reactions provide efficient access to highly substituted carbazoles, furocarbazoles, pyrrolocarbazoles, thiophenocarbazoles, and indolocarbazoles. While tricyclic heterocycles could be derived from vinyl aryl propargylic alcohols, tetra- and pentacyclic heterocycles were synthesized from diaryl propargylic alcohols. The tandem carbonylative benzannulation is initiated by a π-acidic rhodium(I) catalyst-mediated nucleophilic addition to alkyne to generate a key metal-carbene intermediate, which is then trapped by carbon monoxide to form a ketene species for 6π electrocyclization. Overall, three bonds and two rings are formed in all of these tandem carbonylative benzannulation reactions.
- Song, Wangze,Li, Xiaoxun,Yang, Ka,Zhao, Xian-Liang,Glazier, Daniel A.,Xi, Bao-Min,Tang, Weiping
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p. 2930 - 2942
(2016/04/26)
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- Synthesis of Carbazole Alkaloids by Ring-Closing Metathesis and Ring Rearrangement-Aromatization
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Aprocess for the assembly of carbazole alkaloids has been developed on the basis of ring-closing metathesis (RCM) and ringrearrangement-aromatization (RRA) as the key steps. This method is based on allyl Grignard addition to isatin derivatives to provide smooth access to 2,2-diallyl 3-oxindole derivatives through a 1,2-allyl shift. The diallyl derivatives were used as RCM precursors to afford a novel class of spirocyclopentene-3-oxindole derivatives, which underwent a novel RRA reaction to afford carbazole derivatives. The synthetic sequence to carbazoles was shortened by combining the RCM and RRA steps in an orthogonal tandem catalytic process. The utility of this methodology was further demonstrated by the straightforward synthesis of carbazole alkaloids, including amukonal derivative, girinimbilol, heptaphylline, and bis(2-hydroxy-3-methylcarbazole). Just a hop, skip, and a jump away: The addition of allyl Grignard/indium reagents to isatins, ring-closing metathesis (RCM), and ring rearrangement-aromatization (RRA) provided carbazole derivatives in high overall yield (see scheme). The RCM step afforded spirocyclic 3-oxindoles, which underwent acid-catalyzed RRA to give carbazoles. A step-economical tandem RCM/RRA process was also developed and applied to the synthesis of carbazole alkaloids.
- Dhara, Kalyan,Mandal, Tirtha,Das, Joydeb,Dash, Jyotirmayee
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supporting information
p. 15831 - 15835
(2016/01/29)
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- Enantiospecific total syntheses and assignment of absolute configuration of cannabinol-skeletal carbazole alkaloids murrayamines-O and -P
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First enantiospecific total syntheses of the cannabinol-skeletal carbazole alkaloids murrayamines-O and -P isolated from root barks of Murraya euchrestifoli, have been accomplished by highly diastereoselective, Lewis acid catalyzed coupling reactions of commercially available monoterpenes with carbazole derivative, which in addition to confirming the structure also established the absolute configuration of the natural products. Synthesis of both natural products and their enantiomers was achieved with high atom economy, in a protecting-group free manner and in six steps longest linear sequence from commercially available aniline derivative and verbenol.
- Dethe, Dattatraya H.,Das, Saikat,Dherange, Balu D.,Mahapatra, Samarpita
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p. 8347 - 8350
(2015/06/02)
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- Total syntheses of murrayamine E, I, and K
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We describe efficient synthetic routes to murrayamine A (mukoenine C), O-methylmurrayamine A, mahanine, O-methylmahanine, and murrayamine D and the first total syntheses of murrayamine E, I, and K. Key steps are a palladium-catalyzed construction of the carbazole framework and an annulation of the pyran ring, which is either catalyzed by phenylboronic acid or promoted by a Lewis acid.
- Schuster, Christian,Julich-Gruner, Konstanze K.,Schnitzler, Heinrich,Hesse, Ronny,J?ger, Anne,Schmidt, Arndt W.,Kn?lker, Hans-Joachim
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p. 5666 - 5673
(2015/06/16)
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- Amino-directed RhIII-catalyzed C-H activation leading to one-pot synthesis of N-H carbazoles
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One-pot synthesis: An efficient amino-directed one-pot synthesis of N-H carbazoles from unprotected 2-aminobiaryl compounds is reported. The free amino unit acts as both a directing group for ortho C-H activation and a functional group for construction of an N-heterocyclic ring (see scheme). Copyright
- Jiang, Qibai,Duan-Mu, Dandan,Zhong, Wei,Chen, Hao,Yan, Hong
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p. 1903 - 1907
(2013/03/28)
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- Rhodium-catalyzed tandem annulation and (5 + 1) cycloaddition: 3-hydroxy-1,4-enyne as the 5-carbon component
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A Rh-catalyzed tandem annulation and (5 + 1) cycloaddition was realized. 3-Hydroxy-1,4-enyne served as the new 5-carbon component for the (5 + 1) cycloaddition. Substituted carbazoles, dibenzofurans, and tricyclic compounds containing a cyclohexadienone moiety could be prepared efficiently. The identification of a byproduct suggests that metal carbene and ketene intermediates may be involved in the (5 + 1) cycloaddition.
- Li, Xiaoxun,Song, Wangze,Tang, Weiping
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supporting information
p. 16797 - 16800
(2013/12/04)
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- Efficient construction of pyrano [3, 2-a]carbazoles: Application to a biomimetic total synthesis of cyclized monoterpenoid pyrano [3, 2-a]carbazole Alkaloids
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We have developed a highly efficient route to 2-hydroxy-3-methyl-carbazole (1) via a palladium-catalyzed construction of the carbazole skeleton. Using 1 as relay compound, different methods for annulations of pyran rings by reaction with terpenoid building blocks have been tested. The Lewis acid promoted reaction of 1 with prenal (21) opened up an efficient route to girinimbine (3) and the corresponding reaction with citral (25) afforded mahanimbine (5). Oxidation of compounds 3 and 5 provided murraya-cine (4) and murrayacinine (6). Following the biogenetic proposal, mahanim-bine (5) has been exploited for efficient biomimetic syntheses of the cyclized monoterpenoid pyrano[3, 2-a]carbazole alkaloids cyclomahanimbine (7), maha-nimbidine (8) and bicyclomahanimbine (9). The interconversions of 5, 7, 8 and 9 are described and mechanistic implications are discussed. Structural assignments are unambiguously verified by X-ray crystal structure determinations. Moreover, cyclomahanimbine (7) was transformed into murrayazolinine (10) and exozoline (11).
- Hesse, Ronny,Gruner, Konstanze K.,Kataeva, Olga,Schmidt, Arndt W.,Kn?lker, Hans-Joachim
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p. 14098 - 14111
(2013/11/06)
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- Total synthesis of the biscarbazole alkaloids murrafolinea a-d by a domino sonogashira coupling/claisen rearrangement/electrocyclization reaction
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Why take things one step at a time? Aryl-pyran-linked biscarbazole alkaloids of the murrafoline group (see crystal structure of murrafolinea A; dark gray: C, red: O, blue: N) were accessed readily by a novel domino reaction sequence involving Sonogashira
- Kumar, V. Pavan,Gruner, Konstanze K.,Kataeva, Olga,Knoelker, Hans-Joachim
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p. 11073 - 11077
(2013/10/22)
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- Biomimetic Hydroxylation Studies on Carbazole Alkaloids
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3-Methylcarbazole on biomimetic hydroxylation produces 1-hydroxy- and 2-hydroxy-3-methylcarbazoles, a dimeric carbazole (V) and 3-formyl-6-hydroxylcarbazole (VII).
- Roy, Shyamali,Guha, R.,Ghosh, S.,Chakraborty, D. P.
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p. 617 - 618
(2007/10/02)
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- Constituents of Clausena anisata (Willd.) Oliv. (Rutaceae), IV- Synthesis of Mupamine
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This contribution reports on the synthesis of mupamine (6), a pyranocarbazole alkaloid from the root bark of Clausena anisata.
- Mester, Iuliu,Choudhury, Manash Kumar,Reisch, Johannes
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p. 241 - 245
(2007/10/02)
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