Copper(II)-catalyzed asymmetric henry reaction of o-alkynylbenzaldehydes followed by gold(I)-mediated cycloisomerization: an enantioselective route to chiral 1H-isochromenes and 1,3-dihydroisobenzofurans

Abstract

By combining the copper(II)-catalyzed asymmetric Henry reaction of o-alkynylbenzaldehydes with subsequent gold(I)-catalyzed cycloisomerization, optically active 1H-isochromenes and 1,3-dihydroisobenzofurans were successfully synthesized in good overall yields with good to excellent enantioselectivities (up to 98%). Various substrates were investigated, and a correlation between the regioselectivity and electronic nature of the substrates was studied. The substrates with electro-donating groups at the alkynyl moiety preferred a 6-endo-dig manner to generated 1H-isochromenes 3 as main products (up to >30:1) while the ones with electron-withdrawing groups were inclined to undergo 5-exo-dig cyclization to form 1,3-dihydroisobenzofurans 4 (up to 1:5).