An easy route for the synthesis of trisubstituted furans has been demonstrated. One-pot sequential phosphite (H-phosphonate) addition to alkynylaldehydes (enynals) promoted by tripotassium phosphate leads to trisubstituted furans (phosphono-furans) via 5-exo-dig cyclization of the phosphono-alkynol intermediates. In contrast, in the presence of silver(I) tetrafluoroborate, the reaction using the same substrates leads to a diene product.
Key words
nucleophilic addition - enynals - cyclization - isomerization - furans - phosphorus