Functional Group Protecting: The Maimone Synthesis of (+)-Mikanokryptin

Karen Wright and François Couty of the Université de Versailles, following previous reports, converted (Chem. Commun. 2017, 53, 321. DOI: 10.1039/C6CC08294G) 1 into the alkyne 2. Dasan M. Thamattoor of Colby College used (Angew. Chem Int. Ed. 2017, 56, 4499. DOI: 10.1002/anie.201701275) photolysis to release the alkylidene carbene from 3, that then rearranged to 4. This should be a general method for converting ketones to the corresponding alkylidene carbenes.

Patrick G. Steel of the University of Durham deprotected (Tetrahedron Lett. 2017, 58, 17. DOI: 10.1016/j.tetlet.2016.11.084) the aryl allyl ether 5 to give 6, preserving the allyl ester. Hiromi Uchiro of the Tokyo University of Science prepared (Tetrahedron Lett. 2017, 58, 1015. DOI: 10.1016/j.tetlet.2017.01.095) the aryl ether 8 from 7 without eroding the enantiomeric excess. Mahesh K. Lakshman and Barbara Zajc of The City College of New York converted (Synlett 2017, 28, 381. DOI: 10.1055/s-0036-1588350) 9 selectively to 10. Toshimichi Ohmura and Michinori Suginome of Kyoto University established (J. Org. Chem. 2017, 82, 2943. DOI: 10.1021/acs.joc.6b02917) a novel protocol for converting a trimethylsilyl group to the corresponding alcohol. This procedure also proved useful for the conversion of the intramolecular diene cyclozirconation product 11 to the diol 12.

Hiroyuki Konno of Yamagata University devised (Tetrahedron Lett. 2017, 58, 1600. DOI: 10.1016/j.tetlet.2017.03.021) a useful reagent for the protection of an amino acid 13 as the corresponding FMOC derivative 14. Michael A. Schmidt of Bristol-Myers Squibb demonstrated (J. Org. Chem. 2017, 82, 4550. DOI: 10.1021/acs.joc.7b00608) that the 4-cyanobenzenesulfonamide of 15 was stable to many reaction conditions, but could easily be removed on exposure to a thiol to give 16.

α-Amino acids can be protected as the borane adducts, as exemplified by 17. Lennart Bunch of the University of Copenhagen showed (Eur. J. Org. Chem. 2017, 1475. DOI: 10.1002/ejoc.201700063) that 17 could be deprotected to 18 on exposure to TBAF. Hongmei Sun of Soochow University used (Tetrahedron Lett. 2017, 58, 2490. DOI: 10.1016/j.tetlet.2017.05.039) oxidative conditions to couple 19 with the alkene 20, leading to the ester 21.

Tuanli Yao of the Shaanxi University of Science and Technology observed (Org. Lett. 2017, 19, 3135. DOI: 10.1021/acs.orglett.7b01260) that benzyne generated in situ from 23 converted the oxime 22 to the dihydrobenzo[d]oxazole 24. Lei Yu of Yangzhou University used (Adv. Synth. Catal. 2017, 359, 1194. DOI: 10.1002/adsc.201601353) the selenide 25 as a catalyst for the oxidative deprotection of the oxime 22 to the ketone 26.

In the course of a synthesis of the guaianolide (+)-mikanokryptin (29), Thomas J. Maimone of the University of California, Berkeley had to selectively reduce one of the three double bonds of the intermediate triene 27. This problem was solved (Angew. Chem. Int. Ed. 2017, 56, 1624. DOI: 10.1002/anie.201611078) by adding methoxide to the α-methylene lactone, to give, after hydrogenation, the methyl ether 28. The α-methylene lactone was then re-established by base-induced E1cB elimination, leading, after selective oxidation of one of the two allylic alcohols, to 29.