Synthesis of pyridobenzopyrans
-alkylation of salicylaldehyde with the appropriate alkynyl halides followed by Wadsworth - Emmons olefination affords the required substrate for the intramolecular Diels - Alder cyclisation
R = H, Ph
Diels - Alder cyclisations
All cyclisations proceeded smoothly to give the desired tricylic adduct in approximately 40% overall yield
Note that the cinnamyl bromide derived product fully aromatised during the reaction.