Boron Trifluoride-assisted Reactions of 1-Benzothiophen-3(2H)-one with Various Ketones: a Convenient Entry to 2-Methylene-1-benzothiophen-3(2H)-one and/or 6H-Di[1]benzothieno[3,2-b:2,3-e]pyran Derivatives

The title compounds are obtained in moderate to high yields by BF3-assisted reaction of 1-benzothiophen-3(2H)-one with nine ketones in diethyl ether at room temperature; the relative amounts of pyran 1 and ylidene 2 prove to be dependent upon electronic and steric factors.