C-C Bond Construction: The Zhu Synthesis of Goniomitine
Non-enolizable β-keto esters such as 3 are fragile and difficult to prepare. Karl J. Hale of Queen's University Belfast devised (Org. Lett. 2013, 15, 370. DOI: 10.1021/ol303324a) soft enolization conditions for methoxycarbonylation of 1 with 2. Zheng Huang of the Shanghai Institute of Organic Chemistry coupled (Org. Lett. 2013, 15, 1144. DOI: 10.1021/ol400360g) 4 with 5 under Ir catalysis. Tomoya Miura and Masahiro Murakami of Kyoto University combined (Angew. Chem. Int. Ed. 2013, 52, 3883. DOI: 10.1002/anie.201209603) the diazo precursor 8 with the allylic alcohol 7 to give 9, the product of Claisen rearrangement. Tsuyoshi Satoh of the Tokyo University of Science showed (Tetrahedron Lett. 2013, 54, 2533. DOI: 10.1016/j.tetlet.2013.03.025) that the combination of the carbenoid 10 with a ketone enolate 11 led to the cyclopropanol (not illustrated). Jin Kun Cha of Wayne State University found (Org. Lett. 2013, 15, 1780. DOI: 10.1021/ol400666x) that such cyclopropanols coupled with an acid chloride 12 under Pd catalysis to give the diketone 13.
Christopher J. O'Brien of Dublin City University established (Chem. Eur. J. 2013, 19, 5854. DOI: 10.1002/chem.201300546) conditions for the catalytic Wittig reaction of 14 with 15, with in situ reduction of the phosphine oxide. Amir H. Hoveyda of Boston College showed (Org. Lett. 2013, 15, 1414. DOI: 10.1021/ol4004178) that the allene of 17 underwent selective borylation, leading after coupling to the triene 19. Damian W. Young of the Broad Institute demonstrated (Org. Lett. 2013, 15, 1218. DOI: 10.1021/ol400134d) that ring-closing metathesis gave the alkenyl silane 20 with high geometric control. Halogenation could then proceed with either retention or inversion of alkene geometry.
Jianwei Sun of the Hong Kong University of Science and Technology and Zigang Li of the Shenzen Graduate School of Peking University condensed (J. Am. Chem. Soc. 2013, 135, 4680. DOI: 10.1021/ja400883q) the alkyne 22 with 23 to give the trisubstituted alkene 24 with high geometric control. The condensation worked equally well with medium and large ring ethers.
Hua-Jian Xu of the Hefei University of Technology combined (Org. Lett. 2013, 15, 1472. DOI: 10.1021/ol400197y) the bromo alkyne 25 with the carboxylate 26 to give the nitrile 27. Gregory B. Dudley of Florida State University effected (Tetrahedron Lett. 2013, 54, 1312. DOI: 10.1016/j.tetlet.2012.12.122) fragmentation of the triflate 28 to the alkyne 29. Doug E. Frantz of the University of Texas at San Antonio eliminated (J. Am. Chem. Soc. 2013, 135, 4970. DOI: 10.1021/ja401606e) the triflate of the prochiral 30 to deliver the allene 31 in high ee. Keiji Maruoka, also of Kyoto University, developed (Nature Chem. 2013, 5, 240. DOI: 10.1038/nchem.1567) phase transfer conditions for the addition of 32 to 33 to give 34 in high ee.
Jieping Zhu of the Ecole Polytechnique Fédérale de Lausanne coupled (Angew. Chem. Int. Ed. 2013, 52, 3272. DOI: 10.1002/anie.201209970) the alkenyl triflate 35 with the carboxylate 36 to give 37. Several more steps led to the indole alkaloid Goniomitine 38.