variouspositions around the furan ring. The introduction of func-tional groups into the 3- and 4-positions is, however,sometimes difficult since the directlithiation of furanrings followed by the reaction with electrophiles preferen-tially occurs at the 2- or 5-position. Many synthetic meth-ods for the preparation of substituted furans
2-Methylfurans were prepared by an effective cyclization of 1-alkyn-5-ones in the presence of mercuric triflate as the catalyst under very mild reaction conditions with high catalytic turnover up to 100 times. Benzene, toluene, or dichloromethane was the solvent of choice.
Iwanoff, Chemische Berichte, 1954, vol. 87, p. 1600,1604