C-O Ring Construction: The Rizzacasa Synthesis of Trachyspic Acid 19-n-Butyl Ester

Márcio W. Paixão of the Federal University of São Carlos and Burkhard König of the Universität Regensburg assembled 3 by coupling 1 with 2 (Adv. Synth. Catal. 2020, 362, 2367. ). Alexander J. Grenning of the University of Florida prepared the tetrahydrofuran 5 by the thermolysis of 4 (Org. Lett. 2020, 22, 842. ). Delong Liu of Shanghai Jiao Tong University coupled 6 with 7, leading to the dihydrofuran 8 (Org. Lett. 2020, 22, 4680. ). Mykhaylo A. Potopnyk and Sławomir Jarosz of the Polish Academy of Sciences warmed 9 to give an intermediate, to which they added 10, to give 11 (J. Org. Chem. 2020, 85, 3517. ).

Hirokazu Tsukamoto of the Yokohama University of Science developed the reductive cyclization of 12 to the tetrahydropyran 13 (Adv. Synth. Catal. 2019, 361, 3733. ). Xing-Wang Wang of Soochow University, Yuanzhi Xia of Wenzhou University and Zheng Wang of the Shanghai Institute of Organic Chemistry devised the enantioselective hetero Diels-Alder combination of 14 with 15, leading to the dihydropyran 16 (ACS Catal. 2020, 10, 3556. ). Can Zhu, Fahmi Himo and Jan-E. Bäckvall of Stockholm University coupled 17 with 18 to give 19 (J. Am. Chem. Soc. 2020, 142, 5751. ). Frank Hahn of the Universität Bayreuth achieved high diastereoselectivity in the enzymatic cyclization of 20 to 21 (ACS Catal. 2020, 10, 4973. ).

Chaorong Qi of the South China University of Technology used 22 to promote the cyclo-oligomerization of 1, leading to 23 (Chem. Commun. 2020, 56, 6495. ). Iris Antes of the Technical University Munich and Franz Bracher of Ludwig-Maximilians University Munich prepared the macrocycle 25 by the intramolecular Pictet-Spengler cyclization of 24 (Org. Biomol. Chem. 2020, 18, 3047. ). Hirosato Takikawa of the University of Tokyo observed high diastereoselectivity in the thermal rearrangement of 26 to 27 (Tetrahedron Lett. 2020, 61, 151825. ). Satoshi Ichikawa of Hokkaido University optimized the reductive cyclization of 28 to 29 (Org. Lett. 2020, 22, 2697. ).

Trachyspic acid 19-n-butyl ester (32), isolated from the fungus RKGS-F2684, is a selective inhibitor of polo-like kinase 1. Mark A. Rizzacasa of the University of Melbourne assembled 31 by the acid cyclization of 30 followed by ozonolysis and β-elimination (Org. Lett. 2020, 22, 1972. ).