A rhodium and Bronsted acid catalyzed one-pot cycloisomerization/hetero-Diels-Alder reaction of 1,6-enynes with unactivated aldehydes was established under mild conditions. This one-pot catalytic protocol produced a wide variety of annulated dihydropyrans from readily available starting materials in a highly atom economical manner. E.g., in presence of [Rh(cod)2]BF4, BINAP, and PhCO2H, cycloisomerization/hetero-Diels-Alder reaction of 1,6-enyne (I) with 2-MeC6H4CHO gave 85% annulated dihydropyrans (II, III) in a 71:29 ratio. [on SciFinder(R)]