Synthesis of Furan Derivatives. LXXXV. Condensation of Heteroaromatic Aldehydes with Tosylmethyl Isocyanide

Reaction of tosylmethyl isocyanide (2) with heteroaromatic aldehydes, i.e., 2-furaldehyde (1a), 5-nitro-2-furaldehyde (1b) and 5-methoxycarbonyl-2-furaldehyde (1c) ; thiophene-2-carbaldehyde (1d) and 5-nitrothiophene-2-carbaldehyde (1e) ; 1-methylpyrrole-2-carbaldehyde (1f) ; 2-, 3- and 4-pyridinemonocarbaldehyde (1g, 1h and 1i) in the presence of an equimolar amount of potassium carbonate in refluxing methanol afforded the corresponding 5-substituted oxazoles (3a-i). However, a similar treatment of pyrrole-2-carbaldehyde (4) with 2 gave 3-tosylpyrrolo [1,2-c] pyrimidine (6) instead ; a mechanism for this reaction is proposed.