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| - Asymmetric Thio-Claisen Rearrangement Induced by anEnantiopure Alkylsulfinyl Group. Unusual Preference for a BoatTransition State in the Acyclic Series
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| - Ketene aminothioacetals 2a−c and 5a−b bearing an enantiopure vinylic alkylsulfinyl substituentwere readily prepared from (R)-2-cyclohexylsulfinyl-N,N-dimethylethanethioamide 1 with full controlof the geometry of their double bonds. They underwent a Claisen rearrangement upon heating atTHF reflux to afford α-sulfinyl γ-unsaturated thioamides 3a−c and 6a−b. With all substrates theasymmetric induction of the sulfinyl group was excellent. The determination of the absoluteconfigurations of thioamides 3a−c and 6a−b was achieved either by X-ray crystallographic analysisor by chemical correlation. The stereochemical course of this [3,3] sigmatropic transposition wasexplained by an electronic model. Interestingly the Claisen rearrangement of the (ZE)-cinnamylsubstrates 5b was shown to proceed through a boat transition state rather than a chair transitionstate; such a preference is quite unusual for acyclic systems.
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