C-O Ring Construction: The Uchiro Synthesis of GKK1032A₂

Michael J. Krische of the University of Texas, having developed ( 2015, February 23) a general route to diols such as 1, has now described (Chem. Eur. J. 2017, 23, 2557. ) the further conversion to the oxetane 2. Hironao Sajiki and Yoshinari Sawama of Gifu Pharmaceutical University reported (Chem. Commun. 2017, 53, 4787. ) the selective primary phosphorylation that converted 3 to furan 4. This may be an effective route to oxetanes also.

Derek S. Tan of the Memorial Sloan-Kettering Cancer Center observed (J. Org. Chem. 2017, 82, 57. ) remarkable diastereoselectivity in the cyclization of 5 to 6. Christoph Schneider of the Universität Leipzig used (Angew. Chem. Int. Ed. 2017, 56, 6758. ) the diene 8 as a linchpin, assembling 10 by linking with the aldehydes 7 and 9. Shaozhong Ge of the National University of Singapore achieved (J. Am. Chem. Soc. 2017, 139, 6526. ) high ee in the cyclization of 11 to 12. Darunee Soorukram of Mahidol University established (Org. Biomol. Chem. 2017, 15, 3985. ) that exposure of 13 to acid led to selective ionization, and so to cyclization to 14.

James R. Vyvyan of Western Washington University cyclized (Synlett 2016, 27, 2221. ) 15 to the diequatorial tetrahydropyran 16. Perla Ramesh and Yarram Narasimha Reddy of the Indian Institute of Chemical Technology showed (Tetrahedron Lett. 2017, 58, 1037. ) that under the conditions of Sharpless asymmetric epoxidation, the epoxide derived from 17 cyclized via benzylic activation to the ether 18. In a related ionization event, Matthew O'Brien of Keele University found (J. Org. Chem. 2017, 82, 3441. ) that 19 cyclized with high diastereoselectivity to 20.

The allene 21 was a racemic mixture of diastereomers. Nevertheless, Xiaofeng Tong of Changzhou University coupled (Org. Lett. 2017, 19, 1890. ) 21 with 22 to give 23 in high ee.

Amir H. Hoveyda of Boston College improved (Nature 2017, 541, 380. ) geometric control in ring-closing metathesis to form the E macrolactone 25 by starting with the alkenyl borane 24. Erick M. Carreira of the ETH constructed (J. Am. Chem. Soc. 2017, 139, 8082. ) the spirocycle 28 by cyclizing 26 with an Ir catalyst in the presence of benzyl alcohol 27.

Decahydrofluorenes such as GKK1032A₂ (31) show interesting antimicrobial activity. Improving on their previous ( 2012, August 27) route to such natural products, Hiromi Uchiro of the Tokyo University of Science showed (Chem. Asian J. 2017, 12, 628. ) that KH cleanly cyclized 29 to 30.