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Monday, July 28, 2014
Douglass F. Taber
University of Delaware

Arrays of Stereogenic Centers: The Yadav Synthesis of Nhatrangin A

Miquel Costas of the Universitat de Girona developed (J. Am. Chem. Soc. 2013, 135, 14871. ) an iron catalyst for the enantioselective epoxidation of the Z-ester 1. Although the α-chloro aldehyde derived from 3 epimerized under the reaction conditions, Robert Britton of Simon Fraser University showed (Org. Lett. 2013, 15, 3554. ) that the subsequent aldol condensation with 4 favored one enantiomer, leading to 5 in high ee. Other selective aldol condensations of 4, not illustrated, have been reported by Zorona Ferjancic and Radomir N. Saicic of the University of Belgrade (Eur. J. Org. Chem. 2013, 5555. ) and by Tomoya Machinami of Meisei University (Synlett 2013, 24, 1501. ). Motomu Kanai of the University of Tokyo condensed (Org. Lett. 2013, 15, 4130. ) D-arabinose (6) with diallyl amine and the alkyne 7 to give the amine 8 as a mixture of diastereomers. Naoya Kumagai and Masakatsu Shibasaki of the Institute of Microbial Chemistry combined (Angew. Chem. Int. Ed. 2013, 52, 7310. ) 9 and 10 to prepare the α-chiral amine 11.

Tomoya Miura and Masahiro Murakami of Kyoto University used (J. Am. Chem. Soc. 2013, 135, 11497. ) an Ir catalyst to migrate the alkene of 13 to the E allyl boronate, that then added to 12 to give 14. Gong Chen of Pennsylvania State University alkylated (J. Am. Chem. Soc. 2013, 135, 12135. ) the β-H of 15 with 16 to give selectively the diastereomer 17. Geoffrey W. Coates of Cornell University devised (J. Am. Chem. Soc. 2013, 135, 10930. ) catalysts for the carbonylation of the epoxide 18 to either regioisomer of the β-lactone 19. Yujiro Hayashi of Tohoku University combined (Chem. Lett. 2013, 42, 1294. ) the inexpensive succinaldehyde (20) and ethyl glyoxylate 21 to give the versatile aldehyde 22.

Nuno Maulide of the Max-Planck-Institut Mülheim effected (J. Am. Chem. Soc. 2013, 135, 14968. ) Claisen rearrangement of 23 to give, after reduction and hydrolysis, the aldehyde 24. Stephen G. Davies of the University of Oxford reported (Chem. Commun. 2013, 49, 7037. ) a related Claisen rearrangement, not illustrated. Ying-Chun Chen of Sichuan University devised (Org. Lett. 2013, 15, 4786. ) the cascade combination of 25 and 26 to give 27. Helma Wennemers of ETH Zürich added (Angew. Chem. Int. Ed. 2013, 52, 7228. ) the aldehyde 29 to the nitro alkene 28 to give 30. Alessandra Lattanzi of the Università di Salerno combined (Org. Lett. 2013, 15, 3436. ) 31 with 32, leading to the thioether 33.

An aldehyde such as 34 is readily epimerizable. En route to Nhatrangin A (36), Jhillu Singh Yadav of CSIR-Indian Institute of Chemical Technology, Hyderabad found (J. Org. Chem. 2013, 78, 8524. ) that the asymmetric aldol condensation of 34 with propionaldehyde could be carried out without epimerization, to give 35.

D. F. Taber, Org. Chem. Highlights 2014, July 28.
URL: http://www.organic-chemistry.org/Highlights/2014/28July.shtm