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Monday, July 28, 2008
Douglass F. Taber
University of Delaware

Enantioselective Preparation of Secondary Alcohols and Amines

Secondary alcohols can be prepared in high enantiomeric excess by catalytic hydrogenation of ketones. Zhaoguo Zhang of Shanghai Jiaotong University has established (Org. Lett. 2007, 9, 5613. DOI: 10.1021/ol702565x) that β-keto sulfones such as 1 are suitable substrates for this hydrogenation. Reinhard Brückner of the Universität Freiburg has demonstrated (Angew. Chem. Int. Ed. 2007, 46, 6537. DOI: 10.1002/anie.200700021) that the rate of hydrogenation of β-keto esters such as 3 and 5 depends on the alcohol from which the ester is derived, so 3 can be reduced to 4 in the presence of 5.

Enantiomerically-pure secondary alcohols and amines can also be prepared by adding an oxygen or a nitrogen to an existing carbon skeleton. Both Srivari Chandrasekhar of the Indian Institute of Chemical Technology, Hyderabad (Tetrahedron Lett. 2007, 48, 7339. DOI: 10.1016/j.tetlet.2007.08.017) and Arumugam Sudalai of the National Chemical Laboratory, Pune (Tetrahedron Lett. 2007, 48, 8544. DOI: 10.1016/j.tetlet.2007.09.133) have taken advantage of the previously-described enantioselective α-aminoxylation of aldehydes to establish what appears to be a robust preparative route to the enantiomerically-pure epoxides such as 9 of terminal alkenes. Karl Anker Jørgensen of Aarhus University has developed (Chem. Commun. 2007, 3646. DOI: 10.1039/b707844g) a catalyst for the enantioselective addition of 11 to nitroalkenes such as 10. Armando Córdova of Stockholm University has shown (Tetrahedron Lett. 2007, 48, 5976. DOI: 10.1016/j.tetlet.2007.06.110) that epoxy aldehydes such as 14, easily prepared by the protocol he developed, are converted by the Bode catalyst to β-hydroxy esters such as 15.

Hyunsoo Han of the University of Texas, San Antonio has described (Tetrahedron Lett. 2007, 48, 7094. DOI: 10.1016/j.tetlet.2007.08.009) an improved protocol for the enantioselective conversion of primary allylic carbonates 16 to secondary amines 17. René Peters of ETH Zurich has used (Angew. Chem. Int. Ed. 2007, 46, 7704. DOI: 10.1002/anie.200702086) a related procedure for the construction of aminated quaternary centers. Mukund P. Sibi of North Dakota State University has devised (J. Am. Chem. Soc. 2007, 129, 8064. DOI: 10.1021/ja071739c) a catalyst for the conjugate addition of the benzyloxyamine 20 to acyl pyrazoles, and Claudio Palomo of the Universidad de País Vasco has found (Angew. Chem. Int. Ed. 2007, 46, 8054. DOI: 10.1002/anie.200703001) that a simple diphenyl prolinol catalyst will effect enantioselective α-amination of aldehydes.

Carbon-carbon bond formation can also be used to assemble enantiomerically-pure secondary alcohols. Herfried Griengl of Graz University of Technology has found (Adv. Synth. Catal. 2007, 349, 1445. DOI: 10.1002/adsc.200700064) that a commercial nitrile lyase effects addition of nitromethane to an aldehyde such as 24 to give the nitro alcohol 25 in high ee. Markus Kalesse of Leibniz Universität Hannover has constructed a catalyst (Org. Lett. 2007, 9, 5637. DOI: 10.1021/ol702640w) for the enantioselective addition of the ketene silyl acetal 27 to aldehydes. Hajime Ito and Masaya Sawamura of Hokkaido University (J. Am. Chem. Soc. 2007, 129, 14856. DOI: 10.1021/ja076634o) (depicted), and Dennis G. Hall of the University of Alberta (Angew. Chem. Int. Ed. 2007, 46, 5913. DOI: 10.1002/anie.200700975) have reported complementary enantioselective preparations of allyl boronates such as 31.

D. F. Taber, Org. Chem. Highlights 2008, July 28.