Reactions of donor-substituted furans with electrophilic ethylenes

2-Methoxyfuran and 2-p-tolyloxyfuran were attacked at the 5-position by tetracyanoethylene or the super-electrophilic 2,2-bis(trifluoromethyl)ethylene-1,1-dicarbonitrile affording (Z)-3-cyclopropylacrylic esters, substituted in the 3-membered ring. Initially formed zwitterions undergo simultaneous opening of the furan and closure of the cyclopropane ring. In the presence of pyridine, 1,3-prototropy converts the zwitterion to 5-substitution products of the furans.