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.
Keywords: allenoates; annulation; diastereoselectivity; enantioselectivity; organocatalysis.
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.