Preparation of Heterocycles: The Boukouvalas Synthesis of (-)-Auxofuran
Nabyl Merbouh and Robert Britton of Simon Fraser University developed (Eur. J. Org. Chem. 2013, 3219. DOI: 10.1002/ejoc.201300305) a general route to a 2,5-disubstituted furan 3 by taking advantage of the ready α-chlorination of an aldehyde 1. Jérôme Waser of the Ecole Polytechnique Fédérale de Lausanne used (Angew. Chem. Int. Ed. 2013, 52, 6743. DOI: 10.1002/anie.201302210) 5 to oxidize the allene 4 to the furan 6.
Qian Zhang and Xihe Bi of Northeast Normal University used (Angew. Chem. Int. Ed. 2013, 52, 6953. DOI: 10.1002/anie.201302024) Ag catalysis to prepare the pyrrole 9 by coupling the alkyne 7 with the isonitrile 8. Aiwen Lei of Wuhan University reported (Angew. Chem. Int. Ed. 2013, 52, 6958. DOI: 10.1002/anie.201302604) similar results. Professor Lei also developed (Chem. Commun. 2013, 49, 5853. DOI: 10.1039/C3CC42307G) the Pd-catalyzed oxidation of the allyl imine 10 to the pyrrole 11.
Kamal K. Kapoor of the University of Jammu reduced (Tetrahedron Lett. 2013, 54, 5699. DOI: 10.1016/j.tetlet.2013.08.007) the Michael adduct 12 to the pyrrole 13 with triethyl phosphite. Edgar Haak of the Otto-von-Guericke-Universität, Magdeburg condensed (Eur. J. Org. Chem. 2013, 7354. DOI: 10.1002/ejoc.201300803) the alkynyl carbinol 14 with aniline to give the N-phenyl pyrrole 15.
Jean Rodriguez and Thierry Constantieux of Aix-Marseille Université prepared (Eur. J. Org. Chem. 2013, 4131. DOI: 10.1002/ejoc.201300246) the pyridine 18 by combining the ketone 16 and the unsaturated aldehyde 17 with NH4OAc. Teck-Peng Loh of the University of Sciences and Technology of China and Nanyang Technological University found (Angew. Chem. Int. Ed. 2013, 52, 8584. DOI: 10.1002/anie.201301519) that TMEDA was an effective organocatalyst for the assembly of the pyridine 21 from 19 and 20. Andrew D. Smith of the University of St Andrews showed (Angew. Chem. Int. Ed. 2013, 52, 11642. DOI: 10.1002/anie.201306786) that the pyridyl tosylate 24, available by the combination of 22 and 23, readily coupled with both carbon and amine nucleophiles. In a related development, D. Tyler McQuade of Florida State University prepared (Org. Lett. 2013, 15, 5298. DOI: 10.1021/ol4025265) the 2-bromopyridine 26 from the alkylidene malononitrile 25.
Two versatile approaches to substituted indoles were recently described. David F. Wiemer of the University of Iowa cyclized (J. Org. Chem. 2013, 78, 9291. DOI: 10.1021/jo4014244) the Stobbe product 27 to the 3-bromo indole 28. Huw M. L. Davies of Emory University condensed (J. Am. Chem. Soc. 2013, 135, 11712. DOI: 10.1021/ja405043g) the alkyne 29 with tosyl azide to give an adduct that was further cyclized and oxidized to the indole 30.
There are many furan-containing natural products. En route to (-)-Auxofuran (34), John Boukouvalas of the Université Laval took advantage (Org. Lett. 2013, 15, 4912. DOI: 10.1021/ol402345x) of the cycloaddition-retro cycloaddition of 32 with the enantiomerically-pure 31.