Hml. Davies et Bd. Doan, Enantioselective synthesis of fused cycloheptadienes by a tandem intramolecular cyclopropanation/cope rearrangement sequence, J ORG CHEM, 64(23), 1999, pp. 8501-8508
The asymmetric induction in the intramolecular cyclopropanations of allyl v
inyldiazoacetates catalyzed by tetrakis[N-[4-dodecylphenyl)sulfonyl]-(S)-pr
olinato] dirhodium [Rh-2(S-DOSP)(4)] is very dependent on the allyl substit
ution pattern. The reactions of cis-alkenes result in much higher asymmetri
c induction than trans-alkenes while the highest enantioselectivity was obt
ained with a disubstituted terminal alkene. The intramolecular cyclopropana
tion of dienylmethyl vinyldiazoacetates results in the synthesis of fused c
ycloheptadiene ring systems with full control of relative stereochemistry a
nd variable enantioselectivity. The synthetic utility of this process was d
emonstrated by a short synthesis of 5-epi-tremulenolide in 93% ee.