Indium(III) Triflate‐Catalyzed Efficient Prins‐Type Cyclization of β‐Allenols and Aldehydes

We report here an indium(III) triflate (In(OTf) 3 )‐catalyzed Prins‐type cyclization of disubstituted β‐allenols in the presence of aldehydes in dichloromethane (CH 2 Cl 2 ) affording different 3,6‐dihydro‐2 H ‐pyran at room temperature or 45 °C. The high efficiency of the reaction and easily available nature of the starting materials/catalyst make it useful in synthesizing different dihydropyran derivatives. A rationale for the formation of all the products was proposed.