| Enantioenrich allylic alcohols exhibit important biological and medical properties.Therefore,a lot of methods used to synthesize these kinds of compounds have been developed.For example,one of the most efficient and simple approaches to their preparation is the catalytic asymmetric organozinc reagents addition to α,β-unsaturated aldehydes in the presence of a chiral ligand.Aryllithium reagents are one of the least expensive and commonly employed organometallic reagents.They are rarely used in the catalytic addition to aldehydes because of their high reactivity even much more than Grignard reagents.Enantioselective addition of aryllithium reagents to a,β-unsaturated aldehydes to generate enantioenrich secondary allyl alcohols has not been reported.In this thesis,we report a highly asymmetric catalytic addition to a,β-unsaturated aldehydes by using aryllithium reagents.Herein one-pot catalytic asymmetric syntheses of the enantioenrich allylic alcohols beginning from readily available aryl bromides are introduced.Thus,lithium-bormide exchange with commercially available aryl bromides and n-BuLi was followed by salt metathesis with AlCl3 to generate Ar3Al in situ.In the presence of enantioenriched(S)-H8-BINOL as the chiral ligand,ArTi(OiPr)3 coming from Ar3Al with Ti(OiPr)4 was added to α,β-unsaturated aldehydes to afford essentially racemic allylic alcohols.We added TMEDA to eliminate the background reaction catalyzed by LiCI and LiBr to raise the ee value.Under these conditions,enantioenriched allyl alcohols were obtained with up to 99%yield and 94%ee.In this article we disclose the enantioselective addition of aryllithium reagents to α,β-unsaturated aldehydes to generate enantioenrich secondary allyl alcohols,which provides a novel method for synthesis of complex natural products and therapeutic agents. |
