Aromatic Claisen rearrangement enantioselectivity

The Claisen rearrangement has attracted much attention as an attractive tool for the construction of new carbon-carbon bonds. Taguchi et al. reported the enantioselective and regioselective aromatic Claisen rearrangement of catechol mono allylic ether derivatives by means of Corey s chiral boron reagent (Eq. 70) [53a,54]. The mechanism of enantioselectivity is that a rigid five-membered cyclic intermediate is formed by reaction of catechol mono allylic ethers with the chiral boron reagent and this is fol-... 

Rearrangements. By applying Corey s diazaborolidine catalyst to aromatic Claisen rearrangement, a chiral side chain is introduced into the ortho position of catechols. Highly enantioselective rearrangement of 0-allylimidates 111 containing a methoxybinaphthyl substituent has been witnessed. ... 

A highly enantioselective and regioselective aromatic Claisen rearrangement was carried out using the reaction of catechol monoallyl ethers 192 with the chiral boron reagent 193. This reaction occurs without the formation of either the para-rearrangement or the abnormal Claisen rearrangement products (equation 89) . 

Enantioselective aromatic Claisen rearrangement was reported from our group in 1997 [65]. The Claisen rearrangement of catechol mono allyl ether derivative 80 was catalyzed by chiral bis-sulfonamide-boron reagent 81. Although a stoichiometric amount of chiral reagent is required for this reaction, this is only one successful example of the enantioselective aromatic Claisen rearrangement. 

General. Chiral 2-bromo-l,3-bis(4-methylphenyl sulfonyl)-4,5-diphenyl- 1,3,2-diazaborolidine (1) is used to control the stereochemistry of enantioselective aromatic Claisen rearrangements, allylations of aldehydes, aldol reactions, and formation of chiral propa-l,2-dienyl and propargyl alcohols. Included is the discussion of both the R,R) and the (5,5) chiral controllers. 

Taguchi has utilised 86 for the enantioselective aromatic Claisen rearrangement whereas Yammoto has reported the successfiil use of 89 in... 

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