Chemoselective protection of heteroaromatic aldehydes as imidazolidine derivatives : Preparation of 5-substituted furan- and thiophene-2-carboxaldehydes via metallo-imidazolidine intermediates

摘要: Abstract Furan-, thiophene- and N -methylpyrrole-2-carboxaldehydes may be transformed into the corresponding , '-dimethylimidazolidines in a reaction not requiring acid catalysis. The resulting furan thiophene (but -methylpyrrole) derivatives metallated high yields [predominantly at 5 (α-) positions of heteroaromatic rings] carboxaldehyde functionality regenerated under very mild conditions. Treatment aldehydoketone 2-acetyl-5-formylthiophene with '-dimethylethylenediamine gives only product aldehyde function thus establishing this methodology as potentially valuable method for protection an presence ketone.