A theoretical investigation of the intermediacy of alkylidenecarbenes and isonitriles in the formation of furans and oxazoles

Abstract

ab initio Calculations on the mechanisms of conversion of 1-ethynyl-2-hydroxyethene (17a) to furan (17e) and of 1-cyano-2-hydroxyethene (18a) to oxazole (18e) are reported. Structures of stationary points on the reaction potential surfaces were located at the HF/3-21 G level while relative energies were estimated at the MP4SDQ/6-31 G* level plus zero-point vibrational corrections. The alkylidenecarbene (17c) was found not to be a local minimum whereas the isonitrile (18c) was found to be a plausible intermediate during the cyclisation process. The latter lies comfortably in a potential well, making it detectable by spectroscopic means. Again its rearrangement to the cyclic product is rate determining.