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 -benzo[ ]chromenes and hexahydro-1 ,6 -chromeno[6,5- ]chromenone is disclosed here. It involves a [4 + 2] annulation cascade double and triple Michael reactions between curcumins and nitrochromenes in the presence of Cs CO 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.