Organocatalytic access to 5-bromo-3-oxoindane-1-carboxylate enantiomers, good cross-components for the Suzuki coupling

The enantiodivergent Michael addition of allomaltol to 6-bromoinden-1-one assisted by either cinchonidine– squaramide or cinchonine–squaramide hybrid organocatalysts affords the S- or R-configured adducts, respectively; the transformation of the allomaltol moiety in the S-adduct affords the key methyl (1S)-5-bromo-3-oxoindane-1- carboxylate with 99% ee. The subsequent Suzuki–Miyaura cross-coupling, saponification and the Clemmensen reduction proceed with no loss in the ee value and provide a series of (1S)-5-arylindane-1-carboxylic acids. When arylboronic acid contains additional azido group, the cross-coupling product is suitable for the copper(I)-catalyzed cycloaddition with alkynes.