A concise method that is easily amenable for analogue synthesis has been developed
to enantioselectively access 4-amino-3-hydroxybenzopyrans from chalcones. Epoxy alcohols
were formed from chalcones through a Corey–Bakshi–Shibata reduction of the enone and
subsequent Sharpless asymmetric epoxidation of the allylic alcohol. The epoxy alcohols
were protected, regioselectively opened with various amines using catalytic europium(III)
triflate, and the resulting free alcohols were orthogonally protected. Concomitant
deprotection and intramolecular nucleophilic aromatic substitution provided the benzopyran
core, which is poised to undergo additional reactions to provide a diverse chemical
library with ideal properties for biological evaluation.
Key words
natural products - stereoselective synthesis - medicinal chemistry - nucleophilic
aromatic substitution - nitrogen - heterocycles