C-N Ring Construction: The Fujii/Ohno Synthesis of (-)-Quinocarcin
Tsutomu Katsuki of Kyushu University devised (Org. Lett. 2012, 14, 4658. DOI: 10.1021/ol302095r) a Ru catalyst for the enantioselective aziridination of vinyl ketones such as 1. David W. C. MacMillan of Princeton University added (J. Am. Chem. Soc. 2012, 134, 11400. DOI: 10.1021/ja305076b) 3 to the alkene 4 under single electron conditions, to give 5 with high stereocontrol. Barry M. Trost of Stanford University effected (J. Am. Chem. Soc. 2012, 134, 4941. DOI: 10.1021/ja210981a) Pd-catalyzed addition of 7 to an imine 6 to give the pyrrolidine 8. More recently, he used (J. Am. Chem. Soc. 2013, 135, 2459 . DOI: 10.1021/ja312351s) this approach to construct pyrrolidines containing defined quaternary centers.
Christoph Schneider of the Universitšt Liepzig employed (Org. Lett. 2012, 14, 5972. DOI: 10.1021/ol302871u) an organocatalyst to control the relative and absolute configuration not only of the nitrogen-containing ring, but also of the stereogenic center on the sidechain of the pyrrolidone 11. Wei Wang of Lanzhou University also used (Adv. Synth. Catal. 2012, 354, 2635. DOI: 10.1002/adsc.201200538) an organocatalyst to assemble the pyrollidine 14, bearing two stereogenic centers. Using a gold catalyst, Constantin Czekelius of the Freie Universitšt Berlin constructed (Angew. Chem. Int. Ed. 2012, 51, 11149. DOI: 10.1002/anie.201205416) the pyrrolidine 16 having a defined quaternary center.
Motomu Kanai of the University of Tokyo used (J. Am. Chem. Soc. 2012, 134, 17019. DOI: 10.1021/ja308872z) a Cu catalyst to prepare both pyrrolidines and piperidines, by condensing the precursor protected aminal 17 with a ketone 18. Wolfgang Kroutil of the University of Graz effected (Angew. Chem. Int. Ed. 2012, 51, 6713. DOI: 10.1002/anie.201202375) selective enzymatic reductive amination of the methyl ketone of 20 to give, after cyclization and hydrogenation, the 2,6-dialkyl piperidine 21. Ramakrishna G. Bhat of the Indian Institute of Science Education and Research showed (J. Org. Chem. 2012, 77, 11349. DOI: 10.1021/jo302181k) that the reductive cyclization of the amino acid derivative could proceed with high diastereoselectivity, to give 23.
Peter O'Brien of the University of York and Iain Coldham of the University of Sheffield prepared (J. Am. Chem. Soc. 2012, 134, 5300. DOI: 10.1021/ja211398b) both pyrrolidines and piperidines by metalation of an aryl derivative such as 24, followed by alkylation. Shital K Chattopadhyay of the University of Kalyani cyclized (J. Org. Chem. 2012, 77, 11056. DOI: 10.1021/jo3019329) the nitrone 26 to 27 with high diastereoselectivity. Darren J. Dixon of the University of Oxford used (Org. Lett. 2012, 14, 5290. DOI: 10.1021/ol302459c) a tandem combination of organocatalyzed addition followed by gold-catalyzed cyclization to convert 28 into the tetrahydropyridine 30.
Nobutaka Fujii and Hiroaki Ohno of Kyoto University prepared (Angew. Chem. Int. Ed. 2012, 51, 9169. DOI: 10.1002/anie.201205106) the allene 31 as an inconsequential mixture of diastereomers. Cyclization gave the alkyne 32, that they then carried on to (-)-Quinocarcin (33).