Metal-Mediated Construction of Carbocycles: The Pronin Synthesis of Emindole SB

Nuno Maulide of the University of Vienna devised (Angew. Chem. Int. Ed. 2015, 54, 10365. DOI: 10.1002/anie.201503851) conditions for the remarkable de-racemizing cyclization of 1 to 2. Stephen L. Buchwald of MIT achieved (J. Am. Chem. Soc. 2015, 137, 10524. DOI: 10.1021/jacs.5b07061) both high diastereoselectivity and enantioselectivity in the cyclization of 3 to lactone 4.

Mike M. K. Boysen of the Leibniz University of Hannover observed (Org. Lett. 2015, 17, 4132. DOI: 10.1021/acs.orglett.5b01849) high ee in the conjugate addition of 6 to the unsaturated nitrile 5, to give 7. Gang Zhao of the University of Science and Technology of China assembled (Chem. Eur. J. 2015, 21, 9998. DOI: 10.1002/chem.201501806) the cyclopentane 9 in stepwise fashion, organocatalyst-mediated enantioselective conjugate addition of malonate to 8, followed by intramolecular alkylation. Vy M. Dong of the University of California-Irvine effected (Chem. Sci. 2015, 6, 4479. DOI: 10.1039/C5SC01553G) enantioselective intramolecular hydroacylation of the prochiral 10, leading to 11. En route to (-)-galiellalactone, Young-Ger Suh of Seoul National University reduced and deprotected (J. Org. Chem. 2015, 80, 12193. DOI: 10.1021/acs.joc.5b02121) the product from π-allyl cyclization of 12 to give the triol 13.

Xiaoming Zeng of Xi'an Jiaotong University showed (J. Am. Chem. Soc. 2015, 137, 9250. DOI: 10.1021/jacs.5b05868) that the benzene ring of 14 could be selectively hydrogenated under mild conditions, leading to 15. Ken Tanaka of the Tokyo University of Agriculture and Technology combined (Angew. Chem. Int. Ed. 2015, 54, 8241. DOI: 10.1002/anie.201502505) 16, 17, and 18 to give the amide 19. Lili Lin and Xiaoming Feng of Sichuan University developed (J. Org. Chem. 2015, 80, 8836. DOI: 10.1021/acs.joc.5b01318) a zinc catalyst that mediated the addition of 20 to 21 to give 22. Ping Tian of the Shanghai Institute of Organic Chemistry cyclized (Angew. Chem. Int. Ed. 2015, 54, 14815. DOI: 10.1002/anie.201508125) the prochiral p-cresol oxidation product 23 to 24 in high ee.

Jin Kun Cha of Wayne State University showed (Org. Lett. 2015, 17, 5820. DOI: 10.1021/acs.orglett.5b02978) that the cyclopropanol 25 could be cyclized efficiently to 26. A detailed study led Sabine Laschat of the Universität Stuttgart (Chem. Eur. J. 2015, 21, 12396. DOI: 10.1002/chem.201502051) to the methyl/ethyl trisubstituted alkene of 27 as the most favorable for selective ring-closing metathesis to 28.

The paxilline indole diterpenes display an intriguing array of biological activities, but with adjacent cyclic quaternary centers pose a formidable synthetic challenge. Sergey V. Pronin, also of the University of California-Irvine, developed (J. Am. Chem. Soc. 2015, 137, 15410. DOI: 10.1021/jacs.5b11129) an elegant approach to these alkaloids, illustrated by the reductive cyclization of 29 to 30. The aldehyde 30 was carried on by way of intramolecular aldol reaction to Emindole SB (31).