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Monday, January 8, 2018
Douglass F. Taber
University of Delaware

C-O Ring Construction: The Uchiro Synthesis of GKK1032A2

Michael J. Krische of the University of Texas, having developed (Arrays of Stereogenic Centers: The Thomson Synthesis of (-)-Galcatin 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 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 Universitšt 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 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 (Intramolecular Diels-Alder Cycloaddition: 7-Isocyanoamphilecta-11(20),15-diene (Miyaoka),
(-)-Scabronine G (Kanoh), Basiliolide B (Stoltz), Hirsutellone B (Uchiro), Echinopine A (Chen) 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.

D. F. Taber, Org. Chem. Highlights 2017, January 8.