Simple access to 5-carboalkoxy-2,3-dihydro-4H-pyran-4-ones via domino acylative electrocyclization: the first three step total synthesis of the dihydronaphthopyran-4-one class of natural products

Intermolecular domino C-acylation/6π-oxaelectrocyclization between β-ketoesters and α,β-unsaturated acid chlorides took place readily in the presence of CaCl2 to afford a variety of polysubstituted 5-carboalkoxy-2,3-dihydro-4H-pyran-4-ones, in good yields. The products were successfully exploited as precursors, for a simple and efficient construction of a naphthalene fused pyran-4-one ring system. This intramolecular Friedel–Crafts acylative aromatization approach was useful for the synthesis of the phytogrowth inhibiting dihydronaphthopyranone class of natural products.