Abstract
Stereoselective addition of aldehydes 4 to metallated 1-(1-cycloalkenyl)methyl N ,N -diisopropylcarbamates 1 gave cyclic 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 γ-lactones 12 were produced.
Key words
asymmetric synthesis - 1-alkenyl carbamates - homoaldol addition - (-)-sparteine - bicyclic lactones
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