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

The reactions of ethyl diazoacetate with a series of 2-substituted thiophen es in the presence of catalytic rhodium (II) acetate were examined. In the cases of 2-methylthiophene and 2-(trimethylsilyl)thiophene, cyclopropane an d 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-Alkoxythio phenes, however, allowed for the production of a series of ethyl 6-alkoxy-6 -thioxo-2,4-hexadienoates. The mechanistic implications are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.