A NEW CASCADE RING ENLARGEMENT OF ISOXAZOLIDINES FORMED FROM 2-CHLORO-2-CYCLOPROPYLIDENEACETATES

2-Chloro-2-cyclopropylideneacetate 1 and spiropentane analog 2 cycload d pyrroline N-oxide 3 to give spiro[cyclopropane-1,5'-isoxazolidine]s 4 and 5 in good yields; due to the presence of a chlorine substituent on the carbon alpha to the spirocyclopropane ring, which facilitates a cyclopropyl to cyclobutyl ring enlargement, these compounds undergo a cascade rearrangement to yield indolizinone derivatives 8 and 9 clean ly (70-73% yield), offering a new method for the synthesis of the indo lizine skeleton.