Synthesis of Enantioenriched and Diastereomerically Pure cis-Fused Bicyclic α-Oxy-Substituted γ-Lactones via Epoxidation of Optically Active Homoaldol Products
homoaldol adducts 6. By applying the (-)-sparteine method, enantiomerically enriched products were obtained. These were oxidatively cyclized to diastereomerically pure γ-lactones 8 via the γ-lactol ethers 7. After deprotonation of γ-lactones 8 with lithium hexamethyldisilazide, a further substitution was achieved. By trapping the lactone enolates 11 with β-naphthylmethyl bromide, single diastereomers of
Highly enantioenriched 4-hydroxy-1-alkenyl N,N-diisopropylcarbamates, easily available by asymmetric homoaldol reaction, cyclize by treatment with sodium hydride to form (1r,2t,3t)-configured 1-acylcyclopropanes with high diastereoselectivity. The decisive steps are the migration of the N,N-diisopropylcarbamoyl group onto the alkoxide oxygen atom, followed by an intramolecular homoallylic substitution