Synthesis of bicyclic 3-pyrazolidinones via ?-cyclization reactions of exocyclic N-acylhydrazonium ions

Article abstract of DOI:10.1002/recl.19941130304

The preparation of several a-fused 3-pyrazolidinones is described starting from 5,5-dimethyl-3-pyrazolidinone and using an acid-induced cyclization of a ?-nucleophile tethered to N-1 onto a cationic carbon bonded to N-2 (an exocyclic N-acylhydrazonium intermediate).The cyclization reactions proceed best with activated ?-nucleophiles such as allyl- and propargylsilanes.In the case of an ester substituent at the cationic carbon, structural analogues of antibacterial bicyclic pyrazolidinones are obtained.The stereochemistry of one product is established by X-ray crystallographic analysis.Two cyclization products showed NMR spectra with very broad signals due to relatively high nitrogen-inversion barriers (ca. 13 kcal/mole).