Diastereoselective Intramolecular Additions of Allyl- and Propargylsilanes to Iminium Ions: Synthesis of Cyclic and Bicyclic Quaternary Amino Acids

Chiral imino lactones derived from (R)-phenylglycinol containing an allyl- or propargyltrimethylsilyl group in the side chain readily cyclized in the presence of acidic reagents to afford spirocyclic compounds with high diastereoselectivity. Removal of the chiral auxiliary produced 2-substituted 1-aminocycloalkanecarboxylic acids, whereas further cyclizations by means of metathesis or hydroamination reactions led to bicyclic derivatives of pipecolic acid and proline.