1,3-DIPOLAR CYCLOADDITION OF ETHYL DIAZOACETATE WITH (E)-3-ARYLIDENECHROMAN-4-ONES. A NEW ACCESS TO SPIRO-CYCLOPROPANE DERIVATIVES

(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-Delta(2)-pyrazolines ethyl 4'-oxo-4-aryl-spiro[chromanone-3',5-pyrazole]-3-carboxylate 3a-e. The occurrence of Delta(1)-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 N-2 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.