Enantioselective Preparation of Alcohols and Amines
Enzymatic reduction of a ketone can proceed in high enantiomeric excess, but this would require a stoichiometric amount of a reducing agent. Wolfgang Kroutil of the Karl-Franzens-Universität Graz devised (Angew. Chem. Int. Ed. 2008, 47, 741 ) a protocol for preparing the alcohol 2 in high ee starting from the racemic alcohol. The alcohol dehydrogenase chosen was selective for the R alcohol, and the microorganism reduced the ketone so produced selectively to the S alcohol.
James M. Takacs of the University of Nebraska established (J. Am. Chem. Soc. 2008, 130, 3734 ) that chiral Rh catalyzed addition of pinacolborane to a β,γ-unsaturated N-phenyl amide 3 proceeded with high enantiocontrol. The product organoborane was oxidized to the alcohol 4. J. R. Falck of the UT Southwestern Medical Center used (J. Am. Chem. Soc. 2008, 130, 46 ) an organocatalyst to effect addition of phenylboronic acid to the γ-hydroxy enone 5, to give, after hydrolysis, the diol 6. John F. Hartwig of the University of Illinois effectively telescoped (Angew. Chem. Int. Ed. 2008, 47, 1928 ) alcohol formation and protection into a single step, by developing a procedure for the direct conversion of a primary allylic acetate 7 to the enantiomerically-enriched secondary benzyl ether 8.
Tsutomu Katsuki of Kyushu University designed (Chemistry Lett. 2008, 37, 502 ) a catalyst for the enantioselective hydrocyanation of an aldehyde 9, by HCN transfer from the inexpensive 10. Mei-Xiang Wang of the Chinese Academy of Sciences, Beijing and Jieping Zhu of CNRS, Gif-sur-Yvette devised (Angew. Chem. Int. Ed. 2008, 47, 388 ) a catalyst for a complementary one-carbon homologation, the enantioselective Passerini three-component coupling of an aldehyde 12, an isonitrile 13, and an acid 14.
Joseph M. Ready, also of UT Southwestern, developed (J. Am. Chem. Soc. 2008, 130, 7828 ) the preparation of enol benzoates such as 17 from the corresponding alkynes. Sharpless asymmetric dihydroxylation of 17 proceeded with high ee to give, after reduction, the diol 18. Toshiro Harada of the Kyoto Institute of Technology described (Angew. Chem. Int. Ed. 2008, 47, 1088 ) a potentially very practical enantioselective homologation, the catalyzed addition of an alkyl titanium, prepared in situ from the corresponding Grignard reagent, to the aldehyde 19, to give 21 in high ee.
Thomas C. Nugent of Jacobs University Bremen reported (J. Org. Chem. 2008, 73, 1297 ) that added Yb(OAc)3 improved the de in the reductive amination of ketones such as 22 with Raney Ni and 23. Yong-Gui Zhou of the Dalian Institute of Chemical Physics found (Org. Lett. 2008, 10, 2071 ) that cyclic sulfamidates such as 25 were easily prepared from the corresponding hydroxy ketone. Enantioselective hydrogenation of 25 gave 26 with high ee. Note that the cyclic sulfamidates 26 so produced will be versatile intermediates for further transformations, as the O is easily displaced by nucleophiles. Armido Studer of Westfälische-Wilhelms-Universität has been investigating ( 2008, March 24) the radical amination of alkenes. He has developed (Angew. Chem. Int. Ed. 2008, 47, 779 ) an easily-prepared N donor, 28, and found that addition to the alkenyl oxazolidinone 27 proceeded with high de.
The alkene 30 has ten chemically distinct C-H bonds. Paul Müller of the University of Geneva and Robert H. Dodd and Philippe Dauban of CNRS, Gif-sur-Yvette established (J. Am. Chem. Soc. 2008, 130, 343 ) that insertion by a Rh nitrene proceeded with high selectivity primarily into just one of those C-H bonds, delivering 32 in high de.