Trifluoroacetic acid-mediated facile transformation of 2-C-hydroxymethyl-d-glycals to chiral pyrano[2,3-b]benzopyrans

Treatment of 2-C-hydroxymethyl-d-glycals with phenols in trifluoroacetic acid at ambient temperature leads to an extremely facile transformation affording chiral pyrano[2,3-b]benzopyrans in high yields.