Organocatalytic Asymmetric Sequential 1,6-Addition/Acetalization of 1-Oxotetralin-2-carbaldehyde to ortho-Hydroxyphenyl-Substituted para-Quinone Methides for Synthesis of Spiro-3,4-dihydrocoumarins

A chiral squaramide catalyzed approach constructing spiro-3,4-dihydrocoumarin motif by the enantioselective 1,6-addition/acetalization reactions of 1-oxotetralin-2-carbaldehydes and ortho-hydroxyphenyl-substituted para-quinone methides followed by an oxidation was developed. The reactions proceeded smoothly with a wide range of p-QMs and 1-oxotetralin-2-carbaldehydes to generate corresponding products in high yields with excellent diastereoselectivities (>19:1 dr) and enantioselectivities (up to 99% ee).