Heteroaromatic Construction: The Sato Synthesis of (-)-Herbindole

Troels Skrydstrup of Aarhus University devised (Angew. Chem. Int. Ed. 2012, 51, 4681. DOI: 10.1002/anie.201200307) a gold-catalyzed protocol for the condensation of 1 with 2 to deliver the furan 3. Thomas A. Moss of AstraZeneca Mereside found (Tetrahedron Lett. 2012, 53, 3056. DOI: 10.1016/j.tetlet.2012.04.022) that readily-available α-chloro aldehydes such as 4 could be combined with 5 to make the furan 6. This same approach can be used to assemble pyrroles.

Yong-Qiang Tu and Shao-Hua Wang of Lanzhou University developed (J. Org. Chem. 2012, 77, 4167. DOI: 10.1021/jo300374v) a Pd-cascade cyclization that transformed the ester 7 into the pyrrole 8. Cheol-Min Park of the Nanyang Technological University rearranged (Chem. Commun. 2012, 48, 3996, DOI: 10.1039/C2CC30490B; J. Am. Chem. Soc. 2012, 134, 4104, DOI: 10.1021/ja300552c) the oxime ether 10 to the pyrrole 11.

Glenn C. Micalizio of Scripps/Florida established (J. Am. Chem. Soc. 2012, 134, 1352. DOI: 10.1021/ja2105703) a Ti-mediated coupling of 12 with an aromatic aldehyde to deliver the pyridine 13. Yoichiro Kuninobu, now at the University of Tokyo, and Kazuhiko Takai of Okayama University observed (Org. Lett. 2012, 14, 3182. DOI: 10.1021/ol301273j) high regioselectivity in the Re-mediated condensation of 14 with 15 to give the pyridine 16. Douglas M. Mans of GlaxoSmithKline, King of Prussia, cyclized (Org. Lett. 2012, 14, 1604. DOI: 10.1021/ol300351v) the amide 17 to the oxazole (not illustrated), leading, after intramolecular 4 + 2 cycloaddition, to the pyridine 18. Karl Hemming of the University of Huddersfield combined (Org. Lett. 2012, 14, 126. DOI: 10.1021/ol202924s) the cyclopropenone 20 with the imine 19 to construct the pyridine 21.

Shu-Jiang Tu of Xuzhou University and Guigen Li of Texas Tech University condensed (Org. Lett. 2012, 14, 700. DOI: 10.1021/ol203166c) the enamine 22 with the aldehyde hydrate 23 to give the pyrrole 24, that should be readily aromatized to the corresponding indole. Biaolin Yin of the South China University of Technology cyclized (Org. Lett. 2012, 14, 1098. DOI: 10.1021/ol300008d) the furan 25 to the indole 26. Richmond Sarpong of the University of California, Berkeley rearranged (J. Am. Chem. Soc. 2012, 134, 9946. DOI: 10.1021/ja3045647) the alkynyl cyclopropane 27 to an intermediate that was aromatized to the indole 28. Stefan France of Georgia Tech uncovered (Angew. Chem. Int. Ed. 2012, 51, 3198. DOI: 10.1002/anie.201107717) an In catalyst that rearranged the cyclopropene 29 to the indole 30.

Nozomi Saito and Yoshihiro Sato of Hokkaido University cyclized (Org. Lett. 2012, 14, 1914. DOI: 10.1021/ol300571b) 31 to the indoline 32, which they carried on to (-)-Herbindole A (33). To transform the indoline into the indole later in the synthesis, they first deprotected the amine (Na/naphthalene), then oxidized. Likely, exposure of 32 to strong base (Tetrahedron 2012, 68, 4732. DOI: 10.1016/j.tet.2012.04.014) could effect elimination directly to the indole.