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A Diastereoselective Sakurai-Metathesis Route to Dihydrobenzofurans
L. Jiménez-González, S. García-Muñoz, M. Álvarez-Corral, M. Muñoz-Dorado, I. Rodríguez-García*
Universidad de Almería, Spain
24 April 2007 (online)
A short diastereoselective synthesis of cis- or trans-2,3-dihydrobenzofuran using a combined Sakurai-Grubbs metathesis route is described. Using readily available vinylsilane derivatives of phenols, the metathesis step leads to 2,3-dihydrobenzo[f]oxasilepin derivatives which, under typical Sakurai conditions, provide the dihydrobenzofuran products. The diastereoselectivity in the Sakurai process was found to be highly dependent on the electronic nature of the aldehyde. Thus, electron-poor aldehydes lead to cis products, whereas electron-rich aldehydes lead to the formation of the trans isomers. The stereochemistry was assigned by NMR studies and by X-ray crystal structure analysis on representative derivatives. A mechanistic proposal for the Sakurai reaction is given.