Regioselective Synthesis of 2-Alkoxyfurans from Cyclopropenyl Carboxylates

Significance

Reported is a catalyst-controlled cycloisomerization of cyclopropenyl carboxylates to 2-alkoxyfurans. On screening of various catalyst/solvent combinations, it was found that ruthenium affords selectively 2,3,5-substituted furans (A), whereas copper selectively affords 2,3,4-substituted furans (B). The reactions were all conducted in ˜50 mg scale, but the possibility of gram-scale reactions was demonstrated (R^¹ = n-Bu, R^² = CO₂Me, 75% versus 88% yield in mg scale). The substrate scope was well studied and reported yields are moderate to good. No mention is made on the origin of the starting materials; however, a quick literature search showed that they can be synthesized relatively easily from the cor­responding diazo compounds and alkynes.