Claisen condensation of ethyl acetoacetate (I) with ethyl nicotinate (II) using 2.5 equivalents of LDA produced the corresponding diketoester, which was isolated as the enol form (III). Subsequent cyclization of (III) at 150 C with removal of EtOH under reduced pressure afforded pyrone (IV). This was finally coupled with 1-cyclohexene-carboxaldehyde (V) in the presence of L-proline to give the target pyranochromene.

Claisen condensation of ethyl acetoacetate (I) with ethyl nicotinate (II) using 2.5 equivalents of LDA produced the corresponding diketoester, which was isolated as the enol form (III). Subsequent cyclization of (III) at 150 C with removal of EtOH under reduced pressure afforded pyrone (IV). This was finally coupled with (S)-perillaldehyde (V) in the presence of L-proline to give the target pyranochromene.