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■ 1,3-Dipolar Cycloaddition of Ethyl Diazoacetate with (E)-3-Arylidenechroman-4-ones. A New Access to Spirocyclopropane Derivatives

Nadia Wannassi, Hanene Jelizi, Mohamed El Baker Rammah, Kabula Ciamala,* Michael Knorr, Karin Monnier-Jobé, Yoann Rousselin, Marek M. Kubicki, and Carsten Strohmann

*Institute of UTINAM UMR CNRS 6213, Faculty of Science and Technology, University of Franche-Comté, 16 Route de Gray, F-25030 Besançon, France

Abstract

(E)-3-Arylidenechroman-4-ones 1a–e (Ar = Ph, p-MeC6H4, p-MeOC6H4, p-MeSC6H4, p-ClC6H4) react regioselectively (100%) with ethyl diazoacetate 2 in refluxing toluene to afford in good yields spiro-Δ2-pyrazolines ethyl 4’-oxo-4-aryl-spiro[chromanone-3’,5-pyrazole]-3-carboxylate 3a–e. The occurrence of Δ1-pyrazolines as reaction intermediates has been evidenced. The regio- and stereochemistry of spiranic compounds 3a-e has been established on the basis of spectroscopic data and elemental analyses, corroborated by a single crystal X-ray crystallographic analysis of one product 3a. The spiro-adducts 3a–e were brominated by NBS to give spirocyclic-substituted 3-bromo-4,5-dihydro-3H-pyrazoles 4a–e. The latter compounds evolve straightforwardly N2 in refluxing toluene to afford substituted spirocyclic 1-bromocyclopropane-1-carboxylates. The molecular structure of cyclopropane derivative 5e has been determined by means of a single-crystal X-ray diffraction study.