Diels-Alder reactions of carbonyl-containing dienophiles catalyzed by tungstophosphoric acid supported on silica gel

Tungstophosphoric acid (Hg PW12O40) supported on silica gel proved to be an active heterogeneous catalyst for Diels-Alder reactions of enones with var ious dienes. The Diels-Alder adducts were formed in high regio- and/or ster eoselectivity. In some cases the Diels-Alder reactions were accompanied by competing polymerization of the starting compounds. We also found that trif luoromethanesulfonic acid (triflic acid) is an effective homogeneous cataly st for the reaction of unprotected but-3-en-2-one (methyl vinyl ketone) wit h 1,3-cyclohexadiene, albeit with a lower activity than tungstophosphoric a cid.