Expeditious Synthesis of Benzopyrans via Lewis Acid-Catalyzed C−H Functionalization: Remarkable Enhancement of Reactivity by an <i>Ortho</i> Substituent
An expeditious construction of a benzopyran skeleton via Lewis acid-catalyzed C−H functionalization was achieved. In this process, a [1,5] hydride shift and 6-endo cyclization successively occurred to give benzopyrans. The presence of substituents ortho to the alkoxygroup significantly enhanced the reactivity, affording the desired compounds in excellent chemical yields with short reaction times.
C−H Bond Functionalization via Hydride Transfer: Synthesis of Dihydrobenzopyrans from <i>ortho</i>-Vinylaryl Akyl Ethers
作者:Kevin M. McQuaid、Jonathan Z. Long、Dalibor Sames
DOI:10.1021/ol900915p
日期:2009.7.16
The hydride transfer initiated cyclization ("HT-cyclization") of aryl alkyl ethers, which leads to direct coupling of sp(3) C-H bonds and activated alkenes, is reported. Readily available salicylaldehyde derived ethers are converted in one step to dihydrobenzopyrans, an important class of heteroarenes frequently found in biologically active compounds. This process has not been previously reported, in contrast to known HT-cyclizations of the corresponding tert-amines ("tert-amino effect" reactions).