Stereoselective ketene-claisen rearrangement of chiral allylthioethers

The Synthesis and Configurational Stability of Enantioenriched α-Thioallyllithium Compounds and the Stereochemical Course of Their Electrophilic Substitution

“…For the preparation of enantioenriched sec-allyl thiols only two procedures have been published, both involving a route to cyclohex-2-ene-1-thiol. [25,26] Optically active cyclohex-2-en-1-ol (10) with an ee of up to 96% (e.r. ϭ 98:2) was prepared either by kinetic resolution of a racemic cyclohexenol precursor, through lipase-catalyzed enantioselective transesterification [27] [(R) form], or by base-mediated rearrangement of cyclohexene oxide with chiral lithium amide bases [28] [(R) and (S) forms].…”

Die Belluš‐Claisen‐Umlagerung

“…1 H-NMR-spektroskopische Experimente mit dem Verschiebungsreagens (R)-(À)-TFAE (2,2,2-Trifluor-1-(9-anthryl)-ethanol; Tabelle 1) bestätigten den nahezu vollständigen (> 98 %) 1,3-Chiralitätstransfer vom allylischen Kohlenstoffzentrum einer C-S-Bindung in 41 zum stereogenen allylischen Kohlenstoffzentrum in der neu geknüpften C-C-Bindung des chiralen Thioesters 42. [32,33] Belluš-Claisen-Umlagerung Angewandte Chemie [3,3]-Umlagerungsschritt beteiligt, sodass die neue C-C-Bindung bezüglich der ursprünglichen C-S-Bindung ausschließ-lich "cis"-orientiert ist. Die stereochemische Integrität von 42 blieb bei der anschließenden Dechlorierung (Zn in AcOH, 100 8C) zum Thioester 43 erhalten.…”

Investigation of the Chemo‐ and Stereoselectivity of the Ketene‐Claisen Rearrangement

“…To investigate the chirality transfer in acyclic systems and to determine the chemoselectivity (S vs. 0 migration) [5] the ally1 thioethers 11 -13 have been synthesized starting from the commercially available methyl (-)-(S)-lactate 5 (e.e. 2 9 9 % ; Scherne3).…”

“…This investigation is aimed at an intermolecular variant [4] of the [3,3]-sigmatropic rearrangement, in which the zwitterionic intermediates (such as ii or v) are generated in situ by reaction of the allyl thioethers i and iv with dichloroketene (Scheme f). Firstly, the degree of the chirality transfer from the C-S to the C-C bond in the rearrangement of i via the zwitterionic intermediate ii containing a chiral center inside the pericyclic system to iii is analyzed [ 5 ] . Secondly, the chemoselectivity of this rearrangement is investigated by offering dichloroketene to a molecule containing an allylic oxygen-as well as an allylic sulfur-moiety [5].…”

“…Firstly, the degree of the chirality transfer from the C-S to the C-C bond in the rearrangement of i via the zwitterionic intermediate ii containing a chiral center inside the pericyclic system to iii is analyzed [ 5 ] . Secondly, the chemoselectivity of this rearrangement is investigated by offering dichloroketene to a molecule containing an allylic oxygen-as well as an allylic sulfur-moiety [5]. Finally, the asymmetric 1 ,Zinduction in the [3,3]-sigmatropic rearrangement of allyl thioethers (iv + vi) is examined [6].…”