treatment with diazomethane furnished ester 320. Acid-catalyzed opening of the
epoxide was anchimerically assisted by the ester function to give the lactone. The
primary alcohol of the resulting lactones was reduced to a methyl group via the
iodide, and removal of the silyl group yielded lactone 52, which was elaborated
integerrinecic acid lactone.
The synthesis of δ-lactones by an intramolecular Claisen-type condensation of
β-acetoxy amides and imides has been reported by Branda ¨nge and Leijonmarck
[119] (Scheme 72). The syn-aldol acetate ester 321 derived from Oppolzer chiral
auxiliary was subjected to an intramolecular Claisen-type condensation with
LiHMDS to afford β-keto-δ-lactone 322. Conversion of enol 322 into the
corresponding enol tosylate was followed by hydrogenation with H 2 and Pd/C
using MgHPO 4 ∙7H 2 O as acid scavenger, providing δ-lactone 323.
Scheme 69 Canonne et al. one-step spiroannelation to the synthesis of spiro-δ-lactones
Scheme 70 Watt et al. synthesis of δ-lactones
Scheme 71 Synthesis of integerrinecic acid lactone
132
K. Palanichamy and K.P. Kaliappan