Synthesis of Heteroaromatics
Yasutaka Ishii of Kansai University has developed (J. Org. Chem. 2007, 72, 8820. ) a novel route to furans, using a mixed-metal catalyst to effect condensation of an aldehyde or 1,3-diketone such as 1 with an acceptor such as 2 to give the 3-furoate 3. In a complementary approach, Yong-Min Liang of Lanzhou University has found (J. Org. Chem. 2007, 72, 10276. ) that diazoacetate 5 will condense with an alkynyl ketone to give the 2-furoate 6. David W. Knight of Cardiff University has shown (Tetrahedron Lett. 2007, 48, 7709. ) that an alkynyl diol such as 7, readily available by dihydroxylation of the corrresponding alkenyl alkyne, cyclized to the furan on exposure to AgNO3 on silica gel.
Professor Knight has also (Tetrahedron Lett. 2007, 48, 7906. ) established a route to polysubstituted pyrroles 10, by iodination of alkynyl sulfonamides such as 9. Similarly, Richard C. Larock of Iowa State University found (J. Org. Chem. 2007, 72, 9643. ) that I-Cl cyclized methoximes such as 11 to the corresponding iodo isoxazole 12, and Stephen L. Buchwald of MIT uncovered (Org. Lett. 2007, 9, 5521. ) the cyclization of an enamide such as 13 with I2 to the corresponding oxazole 14. In developing a more efficient route to a new class of materials that he has named “triazolamers”, Paramjit S. Arora of New York University was able (J. Org. Chem. 2007, 72, 7963. ) to effect diazo transfer to the amine 15 and subsequent condensation with 16 to give 17, without isolation of the intermediate azide.
C. V. Asokan and E. R. Anabha of Mahatma Gandhi University have described (Tetrahedron Lett. 2007, 48, 5641. ) the activation of a ketone 18 followed by condensation with malononitrile 19 to give the pyridine 20. Hans-Ulrich Reissig of the Freie Universität Berlin has established (Org. Lett. 2007, 9, 5541. ) a complementary three-component coupling of a nitrile 21 with the allenyl anion 22, followed by a carboxylic acid 23 to deliver the pyridine 24. Akio Saito and Yuji Hanzawa of the Showa Pharmaceutical University have reported (Tetrahedron Lett. 2007, 48, 6852. ) the intramolecular Rh-catalyzed cyclization of a methoxime lactone such as 25 to the pyridine 26. Paul Knochel of the Ludwig-Maximilians-Universität München has demonstrated (J. Am. Chem. Soc. 2007, 129, 12358. ) that halogen exchange can be directed by an adjacent carbamate, enabling homologation of 27 to 28.
Professor Buchwald has also developed (Angew. Chem. Int. Ed. 2007, 46, 7236. ) a protocol for the Pd-mediated α-arylation of aldehydes. This procedure converted an o-halo aniline 29 to the indole 31. In a C-H activation-based approach, Mark Lautens of the University of Toronto demonstrated (Org. Lett. 2007, 9, 5255. ) that Pd-catalyzed condensation of 32 with the aniline 33 led to the indole 34.