Regio- and stereoselective synthesis of functionalized tetrahydro-benzochromenes and hexahydrochromenochromenones via [4 + 2] annulation of curcumins with nitrochromenes.

A base-mediated regio- and stereoselective synthesis of functionalized tetrahydro-6 H -benzo[ c ]chromenes and hexahydro-1 H ,6 H -chromeno[6,5- c ]chromenone is disclosed here. It involves a [4 + 2] annulation via cascade double and triple Michael reactions between curcumins and nitrochromenes in the presence of Cs 2 CO 3 and DBU, respectively, at room temperature, and it offers a diverse array of products as single regio- and diastereomers in excellent yields under mild conditions. Preliminary studies towards developing an enantioselective version under organocatalytic conditions met with only limited success but revealed a potentially interesting kinetic resolution pathway.