Lactones. Part 15: Synthesis of chiral spirolactones with a carane system - insect feeding deterrents

Starting from (+)-3-carene 1 several spirolactones with carane backbone were synthesized. delta-Hydroxy-gamma-lactone 5 was obtained by acidic lactonization of a gamma,delta-epoxy ester. Iodolactone 8 and bromolactone 9 were products of iodolactonization of gamma,delta-unsaturated acid 7 and bromolactonization of gamma,delta-unsaturated ester 3 respectively. The halo lactones were subjected to reductive dehalogenation with tributyltin hydride and dehydrohalogenation with DBU. The structures of the lactones obtained were confirmed by X-ray analysis and spectral data. (C) 2002 Elsevier Science Ltd. All rights reserved.