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. ). 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. ). Gaosheng Yang of Anhui Normal University prepared 8 by adding 6 to the aldehyde 7 (Org. Biomol. Chem. 2018, 16, 2688. ). 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. ).

Frank E. McDonald of Emory University used a Pd catalyst to cyclize 11 to the tetrahydropyran 12 (J. Org. Chem. 2018, 83, 6259. ). 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. ). 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. ). Building on the work of Floreancig, Karl A. Scheidt of Northwestern University cyclized 17 to 18 (J. Am. Chem. Soc. 2018, 140, 6212. ).

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. ). 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. ). Professor Miyaoka cyclized 24 to the more stable diastereomer of the spiroketal 25 (J. Org. Chem. 2018, 83, 1976. ). Bernhard Breit of the Albert-Ludwigs-Universität Freiburg dimerized the allene 26 to the macrolide 27 (Angew. Chem. Int. Ed. 2018, 57, 6572. ).

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. ).