| Research Abstract |
1) Diary1-λ^3-iodanes transfer the aryl group to a variety of nucleophiles under mild conditions, probably because of the excellent nucleofugality of the aryliodanyl group. To date, however, no members of this interesting class of diary1-λ^3-iodanes have been synthesized in an optically active form capable of being used in asymmetric synthesis. Reported here for the first time are the synthesis and characterization of the chiral diary1-λ^3-iodanes, 1, 1'-binaphthyl-2-yl(pheny1)-λ^3-iodanes, and their use in a direct asymmetric α-phenylation of enolate anions derived from cyclic β-keto esters.
BF_3-Catalyzed reaction of 2-(diacetoxyiodo)-1, 1'-binaphthyl with tetraphenylstannane evoked tin-λ^3-iodane exchange under mild conditions and afforded chiral 1,1'-binaphthyl-2-yl(phenyl)- λ^3-iodanes. Structure and the absolute configuration of chiralλ^3-iodane were established by single-crystal X-ray analysis.
These chiral diaryliodonium salts were found to undergo direct asymmetricα-phenylation
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by the reaction with enolate anions of cyclicβ-keto esters with 40-50% enantiomeric excess. The chiral 2-iodo-1 ,1'-binaphthyl was easily recovered, without loss of optical purity, and reused. Intramolecular aryl radical trapping experiments suggest a ligand-coupling mechanism on iodine(III) in this phenylation. We believe this is the first demonstration for asymmetric phenylation of metal enolates that does not require using a transition metal catalyst.
2) Recently, we reported the generation of monocarbonyl iodonium ylides and their alkylidene transfer reactions to aldehydes yielding α, β-epoxy ketones. Exposure of Z-(2-acetoxy-1-decenyl)-λ^3-iodanes to EtOLi results in ester exchange to generate the monocarbonyl iodonium ylide with the liberation of ethyl acetate. The monocarbonyl iodonium ylide acts as an alkylidene transfer agent to carbonyl compounds, and the reaction with aldehydes in THF-DMSO gives α, β-epoxy ketones with E-isomers as a major product. Chiral monocarbonyl iodonium ylides with 1, 1'-binaphthyl groups make possible asymmetric synthesis of α, β-epoxy ketones with high enantiomeric excess. Less
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