3-Nitro-3,4-dihydrocoumarins: valuable precursors for the synthesis of enantiomerically enriched masked quaternary α-amino acid derivatives with a 3,4-dihydrocoumarin scaffold

A bifunctional squaramide catalysed asymmetric [4 + 2] cyclization has been developed, which provides an efficient approach for the synthesis of novel chiral masked quaternary α-amino acid derivatives with a 3,4-dihydrocoumarin scaffold.