Intermolecular carbenoid insertions: Reactions of 2-substituted thiophenes with ethyl diazoacetate in the presence of rhodium (II) acetate

The reactions of ethyl diazoacetate with a series of 2-substituted thiophenes in the presence of catalytic rhodium (II) acetate were examined. In the cases of 2-methylthiophene and 2-(trimethylsilyl)thiophene, cyclopropane and thiopyran products predominated while thiophene-2-thiol and 2-(methylthio)thiophene gave rise to thiopyrans and ethyl 2-(2-thienylsulfanyl)acetate. No reaction was apparent when 2-pyrrolidinothiophene was used. 2-Alkoxythiophenes, however, allowed for the production of a series of ethyl 6-alkoxy-6-thioxo-2, 4-hexadienoates. The mechanistic implications are discussed.The reactions of EDA with 2-substituted thiophenes and catalytic Rh2(OAc)4 produced cyclopropanes, thiopyrans and polyenes.