381729-04-0Relevant articles and documents
Stereoselective [2+3] cycloaddition of nitrones to platinum-bound organonitriles. First enantioselective synthesis of Δ4-1,2,4-oxadiazolines
Wagner,Haukka
, p. 2690 - 2697 (2001)
Coordinated benzonitrile in cis-[PtCl2(R3MeSO)(PhCN)] (R3=Me, Ph) is sufficiently activated to undergo [2+3] cycloaddition with nitrones -O+N(R2)=CH(R1) (R1=Ph, p-C6H4Me, p-C6H4OMe, R2=Me; R1=Ph, R2=CH2Ph) under mild conditions to give the corresponding Δ4-1,2,4-oxadiazoline complexes cis-[PtCl2(R3MeSO){N=C(Ph)-ON(R2)- CH(R1)}] in 68-83% yield. In this reaction, the chiral sulfoxide in cis-[PtCl2(PhMeSO)(PhCN)] induces stereoselective formation of the coordinated Δ4-1,2,4-oxadiazoline leading to mixtures of diastereomeric platinum complexes with a d.e. of 30-60%, which can be enhanced to >90% by fractional crystallization. The major diastereoisomer of [PtCl2(PhMeSO){N=C(Ph)-ON(Me)-C(H)Ph}] thus obtained was analyzed by X-ray diffraction and shown to have cis-(R,S) configuration. Reaction of cis-[PtCl2(R3MeSO){N=C(Ph)-ON(R 2)-CH(R1)}] with ethane-1,2-diamine results in displacement of the Δ4-1,2,4-oxadiazolines from the metal and concomitant formation of water-soluble [Pt(en)2]Cl2 and sulfoxide, which can both be removed by aqueous extraction, and this allows for the first time the isolation of Δ4-1,2,4-oxadiazolines in enantiomerically enriched form. Applying this technique to cis-(RS,SC)-[PtCl2(PhMeSO){N=C(Ph)-ON(Me)- C(H)Ph}] of 90% d.e. and 79% e.e. in sulfoxide, the corresponding (R)-2-methyl-3,5-diphenyl- Δ4-1,2,4-oxadiazoline was obtained with 70% e.e.
