One-pot novel regioselective cycloisomerization synthesis of 2-substituted or 3-substituted 4H-furo[3,2-c]chromene through the intermediate cyclopropenes of 3-diazochroman-4-one and phenylacetylene.

A new class of cyclopropenes containing a chroman-4-one motif were synthesized using 3-diazochroman-4-one and phenylacetylene with rhodium(II) catalyst and followed by cycloisomerization to give 2-substituted or 3-substituted 4H-furo[3,2-c]chromene, respectively. Using BF3·Et2O as catalyst, 2-substituted 4H-furo[3,2-c]chromene was exclusively obtained in 70% yield. Using Cu(OTf)2 as catalyst, 3-substituted 4H-furo[3,2-c]chromene was obtained in 95% yield with 98:2 regioselectivity. A one-pot cascade addition-cycloisomerization process was also developed with no need to isolate cyclopropenes of chroman-4-one intermediates.