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Monday, February 21, 2011
Douglass F. Taber
University of Delaware

New Methods for C-C Bond Construction

Luigino Troisi of the University of Salento found (Tetrahedron Lett. 2010, 51, 371. ) that a variety of primary and secondary amines could be coupled with a benzylic halide 1 under carbonylating conditions. Ilhyong Ryu of Osaka Prefecture University showed (Org. Lett. 2010, 12, 1548. ) that under reducing conditions, an iodide 3 coupled with CO to give the primary alcohol. Felicia A. Etzkorn of Virginia Tech observed (Org. Lett. 2010, 12, 696. ) that under Hg hydrolysis conditions, the orthothioester derived from 5 coupled with 6 to give 7. Yasuharu Yoshimi of the University of Fukui and Minoru Hatanaka of Iwate Medical University devised (Tetrahedron Lett. 2010, 51, 2332. ) conditions for the decarboxylative addition of the acid 8 to 9 to give 10. Yong-Min Liang and Xiaojun Yao of Lanzhou University and Chao-Jun Li of McGill University described (J. Org. Chem. 2010, 75, 783. ) a related procedure with α-amino acids.

Yasutaka Ishii of Kansai University established (J. Am. Chem. Soc. 2010, 132, 2536. ) that t-butyl acetate 12 was an effective partner for the Ir-mediated oxidation-coupling-reduction of an alcohol 11. He used (J. Org. Chem. 2010, 75, 1803. ) a similar protocol to condense acetone with the diol 14, to give the long-chain diketone 16.

The formation of allylic Grignard reagents can be inefficient, as the excess reactive halide tends to couple with the Grignard reagent as it forms. Brandon L. Ashfeld of the University of Notre Dame found (Tetrahedron Lett. 2010, 51, 2427. ) a simple solution to this problem, inclusion of a catalytic amount of the inexpensive Cp2TiCl2 to mediate the addition of 18 to 17. Brian T. Connell of Texas A&M demonstrated (J. Am. Chem. Soc. 2010, 132, 7826. ) that with Mn, 21 could be added to 20. The acetate 21 is thus an easily prepared homoenolate equivalent. Note that although 21 is an E/Z mixture, the product 22 is cleanly Z.

Gérard Cahiez of the Université de Paris 13 reported (Synlett 2010, 299. ) a detailed study of the Cu-catalyzed coupling of 24 with 23. Without supporting ligands, slow addition (syringe pump, 1 h) of 24 to 23 assured clean formation of 25. Manual slow addition (dropping funnel, 15 min) was not effective.

The preparatively-useful generation of formyl radicals from aldehydes has long been desired. Maurizio Fagnoni of the University of Pavia found (Chem. Commun. 2009, 7351. ) that a tungstate catalyst under sunlight mediated the conjugate addition of 20 to 26. Unsaturated esters were also efficient acceptors. Stephen Caddick of University College London extended (Chem. Commun. 2010, 46, 133. ) this work to unsaturated sulfones and sulfonates. He found that addition could be effected simply by combining the reactants on water in the presence of air.

The construction of contiguous quaternary alkylated centers is particularly challenging. Steven M. Weinreb of Pennsylvania State University showed (Tetrahedron Lett. 2010, 51, 2032. ) that the protected chloro oxime 28 coupled smoothly with 29 to give 30. In a related development, Don M. Coltart of Duke University found (J. Am. Chem. Soc. 2010, 132, 4546. ) that the tosylhydrazone 31 could be coupled with 32 to give 33.

D. F. Taber, Org. Chem. Highlights 2011, February 21.