Diversity-Oriented Synthesis of Spiropentadiene Pyrazolones and 1<i>H</i>-Oxepino[2,3-<i>c</i>]pyrazoles from Doubly Conjugated Pyrazolones via Intramolecular Wittig Reaction
Pankaj V. Khairnar, Chi-Yi Wu, Yi-Fang Lin, Athukuri Edukondalu, Yi‐Ru Chen, Wenwei Lin
Abstract
An efficient method for the diversity-oriented synthesis of spiropentadiene pyrazolones and 1H-oxepino[2,3-c]pyrazoles is reported. The methodology attributes O-acylation of phosphorus zwitterions which were formed by a tandem phospha-1,6-addition of PBu3 to α,β,γ,δ-unsaturated pyrazolones, further generating betaine intermediates that preferentially resulted in the aforementioned cyclic products in a diversity-oriented manner. The mechanistic investigations revealed that formation of the betaines is the key step to provide the products via an intramolecular Wittig reaction or an unprecedented δ-C-acylation/cyclization/Wittig reaction.
Topics & Concepts
PyrazolonesChemistryWittig reactionIntramolecular forceAcylationBetaineStereochemistryCombinatorial chemistryOrganic chemistryCatalysisPhosphorus compounds and reactionsSynthesis and Reactivity of Sulfur-Containing CompoundsSynthesis and Reactivity of Heterocycles