C-O Ring Construction: The Harran Synthesis of (-)-Callyspongiolide

Ming Wah Wong of the National University of Singapore and Zhihai Ke and Ying-Yeung Yeung of the Chinese University of Hong Kong used 2 to cyclize the prochiral diol 1 to the tetrahydrofuran 3 (ACS Catal. 2018, 8, 850. DOI: 10.1021/acscatal.7b03510). Benjamin List of the Max-Planck-Institut für Kohlenforschung could, with the appropriate organocatalyst, cyclize 4 to either diastereomer of 5 (Science 2018, 359, 1501. DOI: 10.1126/science.aaq0445). Gaosheng Yang of Anhui Normal University prepared 8 by adding 6 to the aldehyde 7 (Org. Biomol. Chem. 2018, 16, 2688. DOI: 10.1039/C8OB00455B). Hiroaki Miyaoka of the Tokyo University of Pharmacy and Life Sciences selectively cyclized the bis epoxide 9 to the lactone 10 (Org. Biomol. Chem. 2018, 16, 3018. DOI: 10.1039/C8OB00603B).

Frank E. McDonald of Emory University used a Pd catalyst to cyclize 11 to the tetrahydropyran 12 (J. Org. Chem. 2018, 83, 6259. DOI: 10.1021/acs.joc.8b00026). Shou-Fei Zhu and Qi-Lin Zhou of Nankai University developed the Ni-catalyzed cyclization of 13 to 14 (J. Am. Chem. Soc. 2018, 140, 7458. DOI: 10.1021/jacs.8b04703). Hajime Yokoyama of the University of Tokoyama also found a Pd catalyst to be effective for mediating the cyclization of 15 to 16 (Heterocycles 2018, 96, 470. DOI: 10.3987/COM-17-13858). Building on the work of Floreancig, Karl A. Scheidt of Northwestern University cyclized 17 to 18 (J. Am. Chem. Soc. 2018, 140, 6212. DOI: 10.1021/jacs.8b03063).

Frank Glorius of the Westfälische Wilhelms-Universität Münster added 19 to racemic 20, leading to the lactone 21 in high ee (J. Am. Chem. Soc. 2018, 140, 3551. DOI: 10.1021/jacs.8b00868). Srihari Pabbaraja of CSIR-Indian Institute of Chemical Technology found that Yamaguchi cyclization was effective for the conversion of 22 to 23 (Tetrahedron Lett. 2018, 59, 2570. DOI: 10.1016/j.tetlet.2018.05.056). Professor Miyaoka cyclized 24 to the more stable diastereomer of the spiroketal 25 (J. Org. Chem. 2018, 83, 1976. DOI: 10.1021/acs.joc.7b02925). Bernhard Breit of the Albert-Ludwigs-Universität Freiburg dimerized the allene 26 to the macrolide 27 (Angew. Chem. Int. Ed. 2018, 57, 6572. DOI: 10.1002/anie.201803369).

Callyspongiolide (30), isolated from Callyspongia sp., shows caspase-independent cytotoxic activity. Patrick G. Harran of UCLA assembled 29 by the cyclocarbonylation of the diol 28. β-Elimination followed by photochemical alkene equilibration led to 30 (J. Am. Chem. Soc. 2018, 140, 1280. DOI: 10.1021/jacs.7b13591).