Lewis acid mediated rearrangements of spiro[2.n]alkane-1,1-dicarboxylates (n = 2–5): an experimental evidence of stepwise 1,2-zwitter-ion formation

The ability of TiCl₄ and GaCl₃ effectively mediate rearrangements of spiro[2.n]alkane-1,1-dicarboxylates (n = 2–5) to (alkylidene)malonates was shown, the mechanism involving formation of 1,2-zwitter-ion species. In the case of TiCl₄, stepwise (alkylidene)malonate formation pathway was postulated that involves preliminary chloride-mediated cyclopropane ring-opening followed by 1,2-H and 1,2-alkyl migrations.