Substituted Benzenes: The Alvarez-Manzaneda Synthesis of (-)-Akaol A
Ramin Ghorbani-Vaghei of Bu-Ali Sina University devised (Tetrahedron Lett. 2012, 53, 2325. DOI: 10.1016/j.tetlet.2012.02.101) conditions for the bromination of an electron deficient arene such as 1. Yonghong Gu of the University of Science and Technology of China found (Tetrahedron Lett. 2011, 52, 4324. DOI: 10.1016/j.tetlet.2011.06.041) that an electron rich anilide 3 could be oxidized to 4. Sukbok Chang of KAIST (J. Am. Chem. Soc. 2012, 134, 2528. DOI: 10.1021/ja211389g) and Kouichi Ohe of Kyoto University (Chem. Commun. 2012, 48, 3127. DOI: 10.1039/C2CC18008A) devised protocols for the oxidative cyanation of 5 to 6.
Phenylazocarboxylates and triazenes are stable, but have the reaction chemistry of diazonium salts. The aromatic substitution chemistry of these derivatives has not been much explored. As illustrated by the conversion of 7 to 8, reported (J. Org. Chem. 2012, 77, 1520. DOI: 10.1021/jo202406k) by Markus R. Heinrich of the Universität Erlangen-Nürnberg, the benzene ring of the phenylazocarboxylate is reactive with nucleophiles. In contrast, triazene-activated benzene rings should be particularly reactive with electrophiles, as exemplified by the transformation, below, of 20 to 21.
Melanie S. Sanford of the University of Michigan observed (Org. Lett. 2012, 14, 1760. DOI: 10.1021/ol300281p) good selectivity for 12 in the Pd-catalyzed reaction of 10 with 11. Jérôme Waser of the Ecole Polytechnique Fédérale de Lausanne used (Org. Lett. 2012, 14, 744. DOI: 10.1021/ol203289v) 14 to alkynylate 13, to give 15.
Sulfonyl chlorides such as 16 are readily prepared from the corresponding arene, and many are commercially available. Jiang Cheng of Wenzhou University found (Chem. Commun. 2012, 48, 449. DOI: 10.1039/C1CC16134B) conditions for the direct cyanation of 16 to 17.
Kenneth M. Nicholas of the University of Oklahoma effected (J. Org. Chem. 2012, 77, 5600. DOI: 10.1021/jo300713h) selective ortho bromination of the carbamate 18, to give 19. Stefan Bräse of KIT observed (Angew. Chem. Int. Ed. 2012, 51, 3713. DOI: 10.1002/anie.201107414) ortho trifluoromethylation of the triazene 20, to give 21. Ji-Quan Yu of Scripps/La Jolla designed (Nature 2012, 486, 518. DOI: 10.1038/nature11158) the benzyl ether 22 to activate the arene for C-C bond formation at the meta position, to give 23.
Guo-Jun Deng of Xiangtan University employed (Org. Lett. 2012, 14, 1692. DOI: 10.1021/ol3002442) a borrowed hydrogen strategy to effect aromatization of 24 with nitrobenzene to give the aniline 25. Zheng-Hui Guan of Northwest University assembled (Org. Lett. 2012, 14, 3506. DOI: 10.1021/ol3014733) the arene 28 by the oxidative combination of 26 and 27.
En route to (-)-Akaol A (32), Enrique Alvarez-Manzaneda of the Universidad de Granada prepared (Chem. Commun. 2012, 48, 606. DOI: 10.1039/C1CC14608D) the diene 29 from (-)-sclareol. Diels-Alder cyclization followed by aromatization then established the aromatic ring of 31.