Calcium-Catalyzed Synthesis of Fused Furo[2,3- b ]furans and Substituted Furans from 2-Oxo Aldehydes and Cyclic Enols.

We report here an atom-economical, syn -diastereoselective synthesis of naphtho-fused furo[2,3- b ]furans along with naphthofurans at room temperature using readily available 2-naphthols and 2-oxo aldehydes using an alkaline earth catalyst [Ca(OTf) 2 ]. 2-Oxo aldehydes having both aryl and alkyl substitutions reacted well. A good number of arenols responded to give fused furans, but selected arenols gave only furofurans. Synthetic applications and gram-scale synthesis were also demonstrated to strengthen this strategy.