C-O Ring Construction: The Smith Synthesis of (+)-18-epi-Latrunculol A
James A. Bull of Imperial College London showed (Angew. Chem. Int. Ed. 2014, 53, 14230. ) that the malonate 1 could readily be cyclized to the oxetane 2. Davide Ravelli of the University of Pavia functionalized (Adv. Synth. Catal. 2014, 356, 2781. ) the α position of the oxetane 3, leading to 5.
Frank Glorius of the Westfälische Wilhelms-Universität Münster hydrogenated (Angew. Chem. Int. Ed. 2014, 53, 8751. ) the furan 6 to give 7 in high ee. Jia-Rong Chen and Wen-Jing Xiao of Central China Normal University converted (Eur. J. Org. Chem. 2014, 4714. ) the initial Henry adduct from 8 into the cyclic ether 9. Anil K. Saikia of the Indian Institute of Technology, Guwahati cyclized (J. Org. Chem. 2014, 79, 8592. ) the ene-yne 10 to the ketone 11. Richard C. D. Brown of the University of Southampton developed (Org. Lett. 2014, 16, 5104. ) a chiral auxiliary that effectively directed the oxidative cyclization of the diene 12 to 13. The chiral auxiliary could be recovered and reused.
K. A. Woerpel of New York University showed (Org. Lett. 2014, 16, 3684. ) that depending on the solvent, 14 could be converted to either 16 or 17. Samuel J. Danishefsky of Columbia University and the Memorial Sloan-Kettering Cancer Center also observed (Chem. Eur. J. 2014, 20, 8731. ) a marked solvent effect on the diastereoselectivity of the reduction of 18 to 19. Xiaoming Feng of Sichuan University added (Chem. Eur. J. 2014, 20, 14493. ) the ketone 20 to Danishefsky's diene 21 to give 22 in high ee. Jhillu Singh Yadav of the Indian Institute of Chemical Technology effected (Tetrahedron Lett. 2014, 55, 3996. ) intramolecular opening of the oxetane of 23 to give, with clean inversion, the cyclic ether 24.
Chun-Yu Ho of the South University of Science and Technology, taking advantage (J. Org. Chem. 2014, 79, 11873. ) of the superior chelating ability of the allyl ether, selectively cyclized 25 to 26. Xuegong She of Lanzhou University used (Angew. Chem. Int. Ed. 2014, 53, 10789. ) a gold catalyst to convert 27 into the eight-membered ring ether 28. Other medium rings could also be constructed using these strategies.
In the course of a synthesis of the selectively cytotoxic macrolide (+)-18-epi-Latrunculol A (31), Amos B. Smith III of the University of Pennsylvania employed (J. Org. Chem. 2014, 79, 9284. ) Mitsunobu conditions to cyclize 29 to 30, with inversion at the secondary center. The product was more easily purified after deprotection with ceric ammonium nitrate.