Academic literature on the topic 'Tricyclic pyrone'

Peter Wipf at the University of Pittsburgh utilized (J. Org. Chem. 2013, 78, 167) an alkynol-furan Diels-Alder reaction to convert 1 into the hydroxyindole 2. An intramolecular Larock indole synthesis was employed (Angew. Chem. Int. Ed. 2013, 52, 4902) by Yanxing Jia at Peking University for the conversion of aniline 3 to tricyclic indole 4. The reaction of boronodiene 5 with nitrosobenzene to produce pyrrole 6 was reported (Chem. Commun. 2013, 49, 5414) by Bertrand Carboni at CNRS University of Rennes and Andrew Whiting at Durham University. The merger of imine 7 with propargyl amine 8 in the presence of a strong base, leading to pyrrole 9, was disclosed (Org. Lett. 2013, 15, 3146) by Boshun Wan at the Chinese Academy of Sciences. Bin Li and Baiquan Wang at Nankai University found (Org. Lett. 2013, 15, 136) that pyrrole 12 could be prepared by the oxidative annulation of enamide 10 with alkyne 11 via ruthenium catalysis in the presence of copper(II). Naohiko Yoshikai at Nanyang Technological University demonstrated (Org. Lett. 2013, 15, 1966) that N-allyl imine 13 could be cyclized to pyrrole 14 via dehydrogenative intramolecular Heck cyclization. Rhett Kempe at the University of Bayreuth developed (Nature Chem. 2013, 5, 140) a “sustainable” pyrrole synthesis in which iridium complex 17 catalyzed the dehydrogenative coupling of alcohol 15 and phenylalaninol (16) to produce pyrrole 18. In a related process, David Milstein at the Weizmann Institute of Science found (Angew. Chem. Int. Ed. 2013, 52, 4012) that the ruthenium complex 20 effected the transformation of 2-octanol (19) and 16 to furnish pyrrole 21. An alternative ruthenium-catalyzed pyrrole synthesis from readily available components was developed (Angew. Chem. Int. Ed. 2013, 52, 597) by Matthias Beller, allowing for the preparation of 25 from ketone 22, diol 23, and amine 24. Meanwhile, with a bit of hetero-aromatic alchemy, Huw M.L. Davies at Emory University converted (J. Am. Chem. Soc. 2013, 135, 4716) the furan 26 to pyrrole 28 by reaction with triazole 27 under rhodium catalysis. Professor Kempe also developed (Angew. Chem. Int. Ed. 2013, 52, 6326) a method for the synthesis of pyridine 30 from amino alcohol 29 and propanol using an iridium catalyst closely related to 17.

The pentacyclic Apocynaceae alkaloid aspidophylline A 3 reverses drug resistance in resistant KB cells. In developing a strategy for the assembly of 3, Neil K. Garg of UCLA envisioned (J. Am. Chem. Soc. 2011, 133, 8877) the intramolecular Pd-catalyzed cyclization of 1 to 2. The starting material for the cyclohexenone derivative 1 was the known tricyclic anhydride 7. This was readily available in gram quantities by oxidation of the commercial pyridone 4. The double decarboxylation to 8 was delicate but could be effected by iterative small-batch microwave heating. Protection of 8 followed by fragmentation and alkylation than delivered 1. The intramolecular Heck cyclization of 1 indeed proceeded smoothly, giving the bicyclic diene 2. Deprotection of the ketone revealed a doubly activated enone, which could be selectively reduced under modifi ed dissolving metal conditions to give the keto ester 12. Alkylation of the lithium enolate with allyl iodide then gave 13, predominantly as the diastereomer illustrated. Reduction followed by selective Johnson-Lemieux oxidative cleavage of the terminal alkene then completed the construction of the diol 14. The vision for the final assembly of the alkaloid was to effect interrupted Fischer indolization of an alkylated cyclohexanone such as 15. To this end, several bicyclic ketones were explored, but none was successful. Finally, attention was turned to the more rigid tricyclic lactone 15. Happily, exposure of 15 to phenylhydrazine in the presence of trifluoroacetic acid led to an intermediate that was not isolated, but directly combined with methanolic K2CO3 to open the lactone, allowing closure of the tetrahydrofuran ring, to give 16. Simple arene sulfonamides can be advantageous in synthesis, as they do not appear as rotameric mixtures in NMR, and are often crystalline. Nevertheless, they have not commonly been used because of the perceived difficulty of deprotection. Sonication of 16 with Mg powder in methanol containing solid NH4Cl led to smooth desulfonylation. Formylation then completed the synthesis of aspidophylline A 3.

Kyungsoo Oh of Chung-Ang University cyclized (Org. Lett. 2015, 17, 450) the chloro enone 1 with NBS to the furan 2. Hongwei Zhou of Zhejiang University acylated (Adv. Synth. Catal. 2015, 357, 389) the imine 3, leading to the furan 4. H. Surya Prakash Rao of Pondicherry University found (Synlett 2014, 26, 1059) that under Blaise conditions, exposure of 5 to three equivalents of 6 led to the pyrrole 7. Yoshiaki Nishibayashi of the University of Tokyo and Yoshihiro Miyake, now at Nagoya University, prepared (Chem. Commun. 2014, 50, 8900) the pyrrole 10 by adding the silane 9 to the enone 8. Barry M. Trost of Stanford University developed (Org. Lett. 2015, 17, 1433) the phosphine-mediated cyclization of 11 to an intermediate that on brief exposure to a Pd catalyst was converted to the pyridine 12. Nagatoshi Nishiwaki of the Kochi University of Technology added (Chem. Lett. 2015, 44, 776) the dinitrolactam 14 to the enone 13 to give the pyridine 15. Metin Balci of the Middle East Technical University assembled (Org. Lett. 2015, 17, 964) the tricyclic pyridine 18 by adding propargyl amine 17 to the aldehyde 16. Chada Raji Reddy of the Indian Institute of Chemical Technology cyclized (Org. Lett. 2015, 17, 896) the azido enyne 19 to the pyridine 20 by simple exposure to I2. Björn C. G. Söderberg of West Virginia University used (J. Org. Chem. 2015, 80, 4783) a Pd catalyst to simultaneously reduce and cyclize 21 to the indole 22. Ranjan Jana of the Indian Institute of Chemical Biology effected (Org. Lett. 2015, 17, 672) sequential ortho C–H activation and cyclization, adding 23 to 24 to give the 2-substituted indole 25. In a complementary approach, Debabrata Maiti of the Indian Institute of Technology Bombay added (Chem. Eur. J. 2015, 21, 8723) 27 to 26 to give the 3-substituted indole 28. In a Type 8 construction, Nobutaka Fujii and Hiroaki Ohno of Kyoto University employed (Chem. Eur. J. 2015, 21, 1463) a gold catalyst to add 30 to 29, leading to 31.