Highly Selective Synthesis of Pyrazole and Spiropyrazoline Phosphonates via Base-Assisted Reaction of the Bestmann–Ohira Reagent with Enones

Novel carbonylated pyrazole phosphonates have been synthesized as single regioisomers by treating conjugated enones, dienones, tropone, and quinone with the Bestmann–Ohira reagent under KOH/EtOH conditions at room temperature. Through an “interrupted” version of the above reaction, carbonylated spiropyrazoline phosphonates have been synthesized from arylidenecycloalkanones under similar conditions (K2CO3/EtOH) with absolute regio- and diastereoselectivity. The key structures were confirmed by detailed spectroscopic analysis and X-ray crystallography.