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Monday, June 16, 2014
Douglass F. Taber
University of Delaware

Preparation of Benzene Derivatives: The Yu/Baran Synthesis of (+)-Hongoquercin A

Lutz Ackermann of the Georg-August-Universität Göttingen oxidized (Org. Lett. 2013, 15, 3484. ) the anisole derivative 1 to the phenol 2. Melanie S. Sanford of the University of Michigan devised (Org. Lett. 2013, 15, 5428. ) complementary conditions for either para acetoxylation of 3, illustrated, or meta acetoxylation. Lukas J. Goossen of the Technische Universität Kaiserlautern developed (Synthesis 2013, 45, 2387. ) conditions for the cascade alkoxylation/decarboxylation of 5 to give 6. Cheol-Hong Cheon of Korea University showed (J. Org. Chem. 2013, 78, 12154. ) that the boronic acid of 7 could act as a blocking group during electrophilic aromatic substitution, or, as illustrated, as an ortho directing group. It could then be removed by protodeboronation.

Jun Wu of Zhejiang University coupled (Synlett 2013, 24, 1448. ) the phenol 9 with the bromo amide 10 to give an ether that on exposure to KOH at elevated temperature rearranged to the intermediate amide, that was then hydrolyzed to 11. Dong-Shoo Shin of Changwon National University reported (Tetrahedron Lett. 2013, 54, 5151. ) a similar protocol (not illustrated) to prepare unsubstituted anilines. Guangbin Dong of the University of Texas, Austin used (J. Am. Chem. Soc. 2013, 135, 18350. ) a variation on the Catellani reaction to convert the ortho bromide 12 to the meta amine 14. Kei Manabe of the University of Shizuoka found (Angew. Chem. Int. Ed. 2013, 52, 8611. ) that the crystalline N-formyl saccharin (16) was a suitable CO donor for the carbonylation of the bromide 15 to the aldehyde 17. John F. Hartwig of the University of California, Berkeley described (J. Org. Chem. 2013, 78, 8250. ) the coupling of the zinc enolate of an ester (Reformatsky reagent), either preformed or generated in situ, with an aryl bromide 18 to give 19.

Olafs Daugulis of the University of Houston developed (Org. Lett. 2013, 15, 5842. ) conditions for the directed ortho phenoxylation of 20 to 22. Yao Fu of the University of Science and Technology of China effected (J. Am. Chem. Soc. 2013, 135, 10630. ) directed ortho cyanation of 23 to 24. Related results were reported (Org. Lett. 2013, 15, 4960. ) by Pazhamalai Anbarasan of the Indian Institute of Technology, Madras. Laura L. Anderson of the University of Illinois, Chicago coupled (Org. Lett. 2013, 15, 3362. ) 26 with 27 to prepare the α-aryl ketone 28. Kian L. Tan, now at Novartis, optimized (J. Am. Chem. Soc. 2013, 135, 18778. ) the silyl tether of 29 to direct selective meta alkenylation.

Jin-Quan Yu and Phil S. Baran of Scripps/La Jolla combined forces (Angew. Chem. Int. Ed. 2013, 52, 7317. ) for the synthesis of (+)-Hongoquercin A (33). Directed regioselective ortho methylation of 31 followed by directed ortho acetoxylation led to 32, that was hydrolyzed to give 33.

D. F. Taber, Org. Chem. Highlights 2014, June 16.
URL: http://www.organic-chemistry.org/Highlights/2014/16June.shtm