BF 3 ·OEt 2 -catalyzed synthesis of 2,2'-spirobi-2 H -1-benzopyrans from 2 H -chromenes.

A new BF 3 ·OEt 2 -catalyzed approach was developed for the construction of 2,2'-spirobi-2 H -1-benzopyrancarboxylates by reacting ethyl 2-(chloromethyl)-2-hydroxy-2 H -chromene-3-carboxylates with salicylaldehydes. The reactions proceeded through the formation of C-C and C-O bonds in one pot. Structure assignment of compound 3c was confirmed by single crystal X-ray analysis.