Magnesium alkylidene carbenoids: Generation from 1-halovinyl sulfoxides with Grignard reagents and studies on their property, mechanism, and some synthetic uses

Magnesium alkylidene carbenoids were generated from 1-halovinyl sulfoxides, derived from ketones and aryl halomethyl sulfoxide, through the ligand exchange reaction of sulfoxides with Grignard reagents. The generated magnesium alkylidene carbenoids were found to be stable at -78 degrees C for over 30 min. The carbenoids reacted with aldehydes to give the adducts in moderate yields; however, they were found to be relatively unreactive to usual electrophiles, The generated magnesium alkylidene carbenoid exists in equilibrium between an alpha-halo alkenyl Grignard reagent and an alkylidene carbene-magnesium halide complex. Halogen exchange and geometrical isomerization of the alkylidene carbenoids were observed. 1-Chlorovinyl sulfoxides reacted with excess aryl Grignard reagents to give alkenyl Grignard reagents having an aryl group. These Gnignard reagents reacted with several electrophiles to give tetra-substituted olefins in moderate to good yields. (C) 1998 Elsevier Science Ltd. All rights reserved.