Heteroaromatic Construction: The Wipf Synthesis of Cycloclavine

Wesley J. Moran of the University of Huddersfield cyclized (Tetrahedron Lett. 2011, 52, 2605. DOI: 10.1016/j.tetlet.2011.03.086) a propargylated ketone 1 with Au to give the furan 2. Shengming Ma of the Shanghai Institute of Organic Chemistry found (Synlett 2011, 931. DOI: 10.1055/s-0030-1259904) that tri(2-furyl)phosphine catalyzed the rearrangement of cyclopropene diesters, prepared by the addition of diazomalonate to alkynes, to the corresponding alkoxy furan 4.

Xihe Bi and Qian Zhang of Northeast Normal University established (Chem. Commun. 2011, 47, 809. DOI: 10.1039/C0CC03802D) that a simple Fe catalyst effected the condensation of 5 with 6 to give the pyrrole 7. Gianfranco Favi of the Università degli Studi di Urbino showed (J. Org. Chem. 2011, 76, 2860. DOI: 10.1021/jo200287k) that the three-component coupling of 8 with an amine 9 and a keton 10 proceeded without catalyst to deliver the pyrrole 11.

Timothy J. Donohoe of the University of Oxford homologated (Org. Lett. 2011, 13, 1036. DOI: 10.1021/ol103088r) 12 by cross metathesis with methyl vinyl ketone, to give, after oxidation and condensation with NH₄OAc, the substituted pyridine 13. Dale L. Boger of Scripps/La Jolla condensed (Org. Lett. 2011, 13, 2492. DOI: 10.1021/ol2007428) the unsubstitued 1,2,3-triazine 15 with an enamine 14 to give 16. Shunsuke Chiba of Nanyang Technological University prepared (J. Am. Chem. Soc. 2011, 133, 6411. DOI: 10.1021/ja200879w) the pyridine 19 by oxidizing the cyclopropanol 17 in the presence of the alkenyl azide 18. Limin Wang of the East China University of Science and Technology prepared (Tetrahedron Lett. 2011, 52, 509. DOI: 10.1016/j.tetlet.2010.11.102) the 2-aminopyridine 23 by the four-component coupling of the aldehyde 20 and the ketone 22 with NH₄OAc and malononitrile 21.

Taking advantage of the Knochel protocol for aryl Grignard formation, Christopher J. Moody of the University of Nottingham combined (Chem. Commun. 2011, 47, 788. DOI: 10.1039/C0CC04306K) the adduct from 24 with the ketone 25 to give the indole 26. Carsten Bolm of RWTH Aachen extended (Org. Lett. 2011, 13, 2012. DOI: 10.1021/ol2004066) the Fe catalysis reported by Zheng to the azide 27 to give 28. Sang-gi Lee of Ewha Womans University found (Org. Lett. 2011, 13, 1350. DOI: 10.1021/ol200045q) that the Blaise adduct from the addition of 29 to the nitrile could be cyclized to the indole 30. Jianbo Wang of Peking University applied (Org. Lett. 2011, 13, 968. DOI: 10.1021/ol103009n) the allene synthesis that he had developed to the aniline 31, to give 33.

We (Tetrahedron 2011, 67, 7195. DOI: 10.1016/j.tet.2011.06.040) reported a systemization of the nine fundamental strategies for indole synthesis. Of those strategies, the rarest is the construction of both rings at once. That approach is elegantly illustrated by the assembly of Cycloclavine 37 devised (J. Am. Chem. Soc. 2011, 133, 7704. DOI: 10.1021/ja2026882) by Peter Wipf of the University of Pittsburgh.