Issue Date: October 13, 2008
Direct Allylic C–H Alkylation Solved
Direct allylic C–H alkylation—coupling a carbon of a nucleophilic molecule to an allyl group (a terminal alkene) of another molecule—is now possible without prefunctionalization by using a Pd(II)/bis(sulfoxide)/benzoquinone catalyst system, chemists from China and the U.S. report. Zhang-Jie Shi and coworkers of Peking University achieved intermolecular alkylations (shown) using allylarene substrates with dicarbonyl nucleophiles (J. Am. Chem. Soc. 2008, 130, 12901). They also showed that some allylic compounds can form cyclic products through intramolecular reactions. Separately, Andrew J. Young and M. Christina White of the University of Illinois, Urbana-Champaign, carried out intermolecular allylic alkylations using aromatic and heteroaromatic allyl substrates with carbonyl- and sulfonyl-based nucleophiles (J. Am. Chem. Soc., DOI: 10.1021/ja806867p). White's group discovered the Pd(II)/bis(sulfoxide)/benzoquinone catalyst system in 2004. Before these two reports, allylic alkylations were normally achieved in two steps through Pd(0)-catalyzed allylic substitution reactions that required installing a functional group at the allylic position. The direct conversion is expected to help streamline the synthesis of small molecules.
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