Enantioselective Construction of Arrays of Stereogenic Centers
An impressive array of new catalysts for enantioselective homologation have been reported. Carlos F. Barbas III of Scripps/La Jolla has found (Angew. Chem. Int. Ed. 2007, 46, 5572 ) that the commercial amino acid 3 mediated the addition of dihydroxyacetone 2 to an aldehyde such as 1 to give the triol 4 with high enantio- and diastereocontrol. Takashi Ooi of Nagoya University has devised (J. Am. Chem. Soc. 2007, 129, 12392) the catalyst 6 for the anti addition (Henry reaction) of nitro alkanes such as 5 to aldehydes. Takayoshi Arai of Chiba University has developed (Organic Lett. 2007, 9, 3595) a complementary catalyst (not shown) that mediated syn addition. Jonathan A. Ellman of the University of California, Berkeley has uncovered (J. Am. Chem. Soc. 2007, 129, 15110) the catalyst 10 for the aza-Henry reaction. Yian Shi of Colorado State University has found (J. Am. Chem. Soc. 2007, 129, 11688) ligands for Pd that direct the absolute sense of the addition of 13 to dienes such as 12. Bernhard Breit of Albert-Ludwigs-Universität, Freiburg has devised conditions (Adv. Synth. Cat. 2007, 349, 1891) for the Rh-catalyzed hydroformylation of α-olefins such as 15, and same-pot proline-catalyzed condensation of the linear aldehyde so produced with a branched aldehyde such as 17 to give, after reductive workup, the branched diol 18. Scott G. Nelson of the University of Pittsburgh has established (J. Am. Chem. Soc. 2007, 129, 11690) conditions, using Cinchona alkaloid derived catalysts, for the condensation of the imine surrogate 19 with the ketene precursor 20, to give the Mannich product 21. Scott E. Schaus of Boston University has developed (J. Am. Chem. Soc. 2007, 129, 15398) a complementary approach, based on catalyzed addition of isolated allyl borinates such as 23 to the activated imine 22. Kálmán J. Szabó of Stockholm University has found (J. Am. Chem. Soc. 2007, 129, 13723) that substituted allyl borinates can be prepared and reacted in situ. Martin Hiersemann of the Universität Dortmund has reported (Organic Lett. 2007, 9, 4979) the remarkable Cu*-catalyzed Claisen rearrangement of the prochiral 24, leading to 25 and thus to the versatile intermediate 27.