Halide Ions as a Highly Efficient Promoter in the Ru-Catalyzed Hydroesterification of Alkenes and Alkynes Eun Ju Park, Ji Min Lee, Hoon Han, and Sukbok Chang* Center for Molecular Design and Synthesis (CMDS), Department of Chemistry and School of Molecular Science (BK21), Korea AdVanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea sbchang@kaist.ac.kr Received July 17, 2006 ABSTRACT The presence of catalytic amounts of halide salts was found to enhance dramatically the reaction efficiency in the Ru-catalyzed hydroesterification of alkenes and alkynes using a chelating 2-pyridylmethyl formate by lowering the reaction temperature. On the basis of IR and NMR studies, the halide effect on the reaction is mainly attributed to the facile dissociation of the trirutheniumcarbonyl precursor into the presumed active metal species. With this milder condition, the substrate scope has been significantly broadened. Functionalization of unsaturated compounds into carbonyl- containing molecules is an area of great interest. 1 We recently reported one notable example of those functionalizations by virtue of Ru 3 (CO) 12 catalyst in the hydroesterification and hydroamidation of double and triple bonds using 2-pyridyl- methyl formate (1, eq 1). 2 The reaction is believed to proceed via a chelation-assisted pathway, 3 and it exhibits excellent efficiency and selectivity with a range of substrates. Additionally, the reaction does not require external CO atmosphere and it can be run even in solvent-free conditions. The chelating auxiliary, 2-pyridine- methanol, can be quantitatively recovered after hydrolysis of the produced esters, thus offering additional merits. Despite these advantages, the reaction usually requires relatively high temperatures and a large excess of substrates, which provide difficulties for making this one-carbon ho- mologating protocol more practical. Although several aspects may be considered to improve the reaction conditions, 4 we envisioned that the generation of catalytically more active (1) For selected examples of hydroacylation of alkenes, see: (a) Lochow, C. F.; Miller, R. G. J. Am. Chem. Soc. 1976, 98, 1281-1283. (b) Marder, T. B.; Roe, D. C.; Milstein, D. Organometallics 1988, 7, 1451-1453. (c) Bosnich, B. Acc. Chem. Res. 1998, 31, 667-674. (d) Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 11492-11493. (e) Sato, Y.; Oonishi, Y.; Mori, M. Angew. Chem., Int. Ed. 2002, 41, 1218-1221. (f) Tanaka, M.; Sakai, K.; Suemune, H. Curr. Org. Chem. 2003, 7, 353-367. (g) Kakiuchi, F.; Chatani, N. Top. Organomet. Chem. 2004, 11, 45-79. (2) (a) Ko, S.; Na, Y.; Chang, S. J. Am. Chem. Soc. 2002, 124, 750- 751. (b) Na, Y.; Ko, S.; Hwang, L. K.; Chang, S. Tetrahedron Lett. 2003, 44, 4475-4478. (c) Ko, S.; Lee, C.; Choi, M.-G.; Na, Y.; Chang, S. J. Org. Chem. 2003, 68, 1607-1610. (d) Ko, S.; Han, H.; Chang, S. Org. Lett. 2003, 5, 2687-2690. (3) For some selected examples, see: (a) Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda, M.; Chatani, N. Nature 1993, 366, 529-531. (b) Itami, K.; Koike, T.; Yoshida, J.-i. J. Am. Chem. Soc. 2001, 123, 6957-6958. (c) Han, H.; Bae, I.; Yoo, E. J.; Lee, J.; Do, Y.; Chang, S. Org. Lett. 2004, 6, 4109-4112. (d) Ko, S.; Kang, B.; Chang, S. Angew. Chem., Int. Ed. 2005, 44, 455-457. ORGANIC LETTERS 2006 Vol. 8, No. 19 4355-4358 10.1021/ol061753e CCC: $33.50 © 2006 American Chemical Society Published on Web 08/24/2006