BF3 center dot OEt2-catalyzed synthesis of 2,2 '-spirobi-2H-1-benzopyrans from 2H-chromenes

A new BF3 center dot OEt2-catalyzed approach was developed for the construction of 2,2'-spirobi-2H-1-benzopyrancarboxylates by reacting ethyl 2-(chloromethyl)-2-hydroxy-2H-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.