C-H bond functionalization via hydride transfer: synthesis of dihydrobenzopyrans from ortho-vinylaryl akyl ethers.

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).