Heterolytic fragmentation of 4-hydroxy-6,6,7,7-tetramethyl-Δ2-dehydro-quinuclidine-2,3-dicarboxylic acid esters

The title quinuclidines undergo cleavage under the action of acids or H₂O to give Δ²-dehydro-4-piperidones 4, 5 and isobutylene; the resulting redistribution of bond lengths upon N-protonation has been demonstated by X-ray diffraction methods for picrate 2a as well as by ab initio calculations for quinuclidine la, cation 2a’ and zwitterion 2a”, the latter being the most suitable as an intermediate of the fragmentation.