2‐Cyclopentenyl‐ and 2‐cyclohexenylmethyl sulfoximines can be converted into angular carbon‐functionalised, highly substituted, isomerically pure (ds ≥ 98%) 2‐oxabicyclo[3.3.0]octanes and 2‐oxabicyclo[3.4.0]nonanes in high yields by a convenient one‐pot sequence. Molecular frameworks such as these can be found in many biologically active natural products. In addition to the methodological work, we report on studies towards the total synthesis of the euglobals G1 and G2 and arenaran A.
1999 stereochemistry stereochemistry (general, optical resolution) O 0030
-031Metalated 2-Alkenyl Sulfoximines in Asymmetric Synthesis: Regioand Stereoselective Synthesis of Highly Substituted Oxabicyclic Ethers and Studies Towards the Total Syntheses of the Euglobals G1 and G2 and Arenaran A.-Chiral cyclopentenylmethyl and cyclohexenylmethyl sulfoximines (I) and (IV) undergo a titanation-γhydroxyalkylation-fluoride ion-induced cyclization sequence to furnish the diastereomerically pure cis-fused bicyclic ethers (III) and (V), resp., in a convenient one-pot procedure. The absolute configuration at C-4 and C-5 (formed in the hydroxyalkylation step) and at C-1 (formed during the cyclization step) is exclusively controlled by the absolute configuration at the sulfur atom, while the absolute configuration at C-3 is introduced by the chiral aldehyde (II). All attempts to extend this cyclization methodology to the synthesis of euglobals (IX) and arenaran A (X) are not successful despite extensive studies. The best result obtained in such an approach is the formation of tricyclic compound (VIII) in 5% yield. -(REGGELIN, MICHAEL; GERLACH, MATTHIAS; VOGT, MELANIE; Eur.
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