A new cascade ring enlargement of isoxazolidines formed from 2-chloro-2-cyclopropylideneacetates

Abstract

2-Chloro-2-cyclopropylideneacetate 1 and spiropentane analog 2 cycloadd 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 α 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 cleanly (70–73% yield), offering a new method for the synthesis of the indolizine skeleton.