Carbon-Carbon Bond Formation: The Rhagavan Synthesis of Nupharamine
David Milstein of the Weizmann Institute of Science used (J. Am. Chem. Soc. 2016, 138, 6985. DOI: 10.1021/jacs.5b13208) a Mn pincer complex to catalyze the conjugate addition of the nitrile 1 to 2 to form 3. Larry E. Overman of the University of California, Irvine generated (Org. Lett. 2016, 18, 2564. DOI: 10.1021/acs.orglett.6b00895) a radical photochemically from 5 that added to 4, leading to lactone 6. Magnus Rueping of RWTH Aachen prepared (Angew. Chem Int. Ed. 2016, 55, 6776. DOI: 10.1002/anie.201511235) 9 by the light-activated addition of 7 to 8. Yoshito Kishi of Harvard University optimized (J. Am. Chem. Soc. 2016, 138, 7178. DOI: 10.1021/jacs.6b03897) the preparation of 12 by the Fukuyama coupling of 10 with 11.
Ken-ichi Shimizu of Hokkaido University established (Chem. Eur. J. 2016, 22, 6111. DOI: 10.1002/chem.201505109) a simple protocol for the conversion of the primary alcohol 13 to the alkene 15. Bernhard Breit of the Albert-Ludwigs-Universität Freiburg effected (Chem. Commun. 2016, 52, 5840, DOI: 10.1039/C6CC02272C; Org. Lett. 2016, 18, 124, DOI: 10.1021/acs.orglett.5b03391) the allylic coupling of the alkyne 16 with the keto acid 17 to give 18. Doug E. Frantz of the University of Texas at San Antonio devised (Angew. Chem Int. Ed. 2016, 55, 6689. DOI: 10.1002/anie.201601899) conditions to convert a β-keto ester cleanly into either geometric isomer of the corresponding enol carbamate 19. Fe-catalyzed coupling of 19 with the Grignard reagent 20 led to 21. Cristina Nevado of the University of Zürich constructed (Angew. Chem. Int. Ed. 2016, 55, 6938. DOI: 10.1002/anie.201601296) the trisubstituted alkene 25 by the three-component coupling of 22, 23, and 24.
Chen Zhu of Soochow University assembled (Angew. Chem. Int. Ed. 2016, 55, 2866. DOI: 10.1002/anie.201510973) the ketone 28 by the oxidative cleavage of 26 in the presence of 27. Yiyun Chen of the Shanghai Institute of Organic Chemistry (J. Am. Chem. Soc. 2016, 138, 1514. DOI: 10.1021/jacs.5b13066) and Hua Fu of Tsinghua University (Chem. Commun. 2016, 52, 7292. DOI: 10.1039/C6CC01632D) reported related results. Chao-Jun Li of McGill University observed (Chem. Eur. J. 2016, 22, 5888. DOI: 10.1002/chem.201600219) high diastereoselectivity in the preparation of the ester 30 by the coupling of 24 with 29.
Jan-E. Bäckvall of Stockholm University found (Angew. Chem. Int. Ed. 2016, 55, 3734. DOI: 10.1002/anie.201511139) that the formation of the allene 33 by the Fe-catalyzed coupling of 32 with the ester 31 proceeded with substantial retention of ee. Xiaodong Shi of the University of South Florida also observed (Chem. Commun. 2016, 52, 296. DOI: 10.1039/C5CC08233A) that the formation of the allene 35 by the Fe-catalyzed coupling of 24 with the alcohol 34 proceeded with substantial retention of ee.
In addition to ketone enolate alkylation and aldol condensation/dehydration there is a third way, as illustrated (Org. Biomol. Chem. 2016, 14, 131. DOI: 10.1039/C5OB01750E) by Sadagopan Raghavan of the Indian Institute of Chemical Technology. Chlorination of the sulfide precursor to 36 followed by direct condensation with the silyl enol ether 37 in the presence of catalytic ZnBr2 led to 38, that was readily desulfurized and carried on to nupharamine (39).