Aluminum Triflate Catalyzed Tandem Reactions of d-Galactal: Toward Chiral Benzopyrans, Chromenes, and Chromans

3,4,6-Tri-O-acetyl-d-galactal is selectively converted into 1-O-aryl-2-deoxy derivatives or chiral bridged benzopyrans under Al(OTf)3 catalysis, depending on reaction conditions. The benzopyrans react with Al(OTf)3/acetic anhydride in ring-opening reactions in the absence or presence of acetic acid to selectively produce chiral chromenes or chromans, respectively, in high yields.