Synthesis of 3-benzylidene-dihydrofurochromen-2-ones: Promising intermediates for biflavonoid synthesis

A route to 3-benzylidene-dihydrofurochromen-2-ones from 2H-chromenes is described. Lactonization of 2H-chromenes was achieved using a two-step cyclopropanation-rearrangement sequence. Subsequent conversion of these intermediates to the corresponding α-benzylidene lactones was achieved by lithium enolate aldol reaction, followed by base-promoted elimination of the aldolate mesylates. The alkene geometry was found to be base-dependent. While the use of KOBut favored formation of the E isomer, the application of DBU showed a slight preference for the Z isomer. In further studies, these 3-benzylidene-dihydrofurochromen-2-ones were converted to polyaromatic structures possessing all the required functionality for biflavonoid synthesis.