A New Approach to β-Fluoropyrroles Based on the Michael Addition of Isocyanomethylide Anions to α-Fluoroalkenyl Sulfones and Sulfoxides

The reactions of 2-aryl-1-fluorovinyl phenyl sulfones with carbanions derived from isocyanoacetates gave mixtures of 3-aryl-4-fluoro-2-pyrrolecarboxylates and 3-aryl-4-fluoro-4-phenylsulfonyl-2-isocyanobutanoates, simple Michael addition products, in variable ratios depending upon the conditions employed. On the other hand, the reaction of 1-fluoro-1-propenyl phenyl sulfone afforded mainly the simple Michael addition products in moderate yields as well as a small amount of 4-phenylsulfonyl-3-methyl-2-pyrrolecarboxylates and a trace amount of 4-fluoro-3-methyl-2-pyrrolecarboxylates. 1-Fluoropropenyl phenyl sulfoxide underwent mainly the simple Michael addition to give butenoates and a small amount of 4-fluoro-2-pyrrolecarboxylates.