Enantioselective Catalytic [4+1]-Cyclization of ortho-Hydroxy-para-Quinone Methides with Allenoates.

The first highly asymmetric catalytic synthesis of densely functionalized dihydrobenzofurans is reported, which starts from ortho-hydroxy-containing para-quinone methides. The reaction relies on an unprecedented formal [4+1]-annulation of these quinone methides with allenoates in the presence of a commercially available chiral phosphine catalyst. The chiral dihydrobenzofurans were obtained as single diastereomers in yields up to 90 % and with enantiomeric ratios up to 95:5.