Axially chiral dicarboxylic acids

Axially chiral dicarboxyhc acids were introduced by Mamoka and coworkers as a new class of Bronsted acid catalysts in 2007 [176]. The enantioselective Mannich 

As mentioned earlier, a review of key developments in the use of chiral phosphoric acids will be provided by Professor Akiyama in the Chapter 11. It is also worth noting that recent years have seen the development of other strong Bronsted acids with the binaphthalene backbone, such as those by the Yamamoto [182-185], list [186-189], and Toste groups [190]. 

After the manuscript of this chapter was written, several reports were published on the catalysis of various transformations using chiral alcohols and silanols [191, 192], squaramides [193-197], guanidines [198-201], amidiniums [202], iminophos-phoranes and triazoliums [203-205], dicarboxyUc acids [206], and other strong Bronsted acids [207, 208]. 

1 McGilvra, J.D., Gondi, V.B., and Rawal, V.H. (2007) Asymmetric proton catalysis, in Enantioselective Organocatalysis (ed. P.I. Dalko), Wiley-VCH Verlag GmbH, Weinheim, pp. 189-254. 

7 Jeffrey, GJV. (1997) An Introduction to Hydrogen Bonding, Oxford University Press, New York. 

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Scheme 24.21 Asymmetric addition to imines catalysed by axially chiral dicarboxylic acids.

Finally, a direct Mannich-type approach has been developed for the enantioselective synthesis of hydrazines and amines (Scheme 16.40). Thus, by trapping with alkyl diazoacetates some in s/iw-generated acyclic azomethine imines, in the presence of axially chiral dicarboxylic acids, a series of a-diazo-(3-hydrazino esters were obtained with excellent enantioselectivities [86]. 

In 2012, Maruoka and coworkers developed a new catalytic asymmetric Ugi-3CR through the use of an axially chiral dicarboxylic acid 27 [28], In the approach, a variety of aldehydes, 2-benzoyloxyphenyl isocyanide (26), and an acyclic azomethine imine 25 were initially reacted, yielding heterocyclic compounds 28 in excellent yields and good enantiomeric excesses (Scheme 7.11). Upon acid hydrolysis of the heterocyclic compound 28a, the corresponding a-hydrazino amide 29 was obtained without loss of enantioselectivity (bottom-left. Scheme 7.11). 

Maruoka and co-workers reported the first catalytic asymmetric three-component 1,3-dipolar cycloaddition of terminal alkynes with acyclic azomethine imines generated in situ from the corresponding aldehydes and hydrazides, which was realized using CuOAc/Ph-pybox and axially chiral dicarboxylic acid cocatalysts (Scheme 27) [48]. This transformation has abroad tolerance with regard to the substrates, affording diverse chiral 3,4-disubstituted pyrazolines with high enantioselectivities. The role of the axially chiral dicarboxylic acid is to generate the protonated acyclic azomethine imine, which then reacts with chiral Cu-acetylide. 

The axially chiral dicarboxylic acid 27b was also uniquely reactive in achieving the highly enantioselective addition of aldehyde N,N-diaIkylhydrazones, a readily... 

Recently, Maruoka and coworkers have also developed an asymmetric inverse electron demand 1,3-dipolar cycloaddition of C,A -cyclic azomethine imines with fort-butyl vinyl ether catalyzed by a newly developed axially chiral dicarboxylic acid having diarylmethyl groups at the 3,3 -positions (Scheme 7.7) [18]. Based on this finding, the concept of the inverse electron demand umpolung 1,3-dipolar cycloaddition was introduced as a strategy for switching the regioselectivity of the cycloaddition from that of the titanium BINOLate-catalyzed normal electron demand 1,3-dipolar cycloaddition with enals (Table 7.3) by... 

In 2007, Maruoka et al. introduced chiral dicarboxylic acids consisting of two carboxylic acid functionalities and an axially chiral binaphthyl moiety. They applied this new class of chiral Brpnsted acid catalyst to the asymmetric alkylation of diazo compounds withA-Boc imines [91]. The preparation of the dicarboxylic acid catalysts bearing aryl groups at the 3,3 -positions of the binaphthyl scaffold follows a synthetic route, which has been developed earlier in the Maruoka laboratory [92]. 

Asymmetric inverse-electron-demand 1,3-dipolar cycloaddition of C,A-cyclic azomethine imines with c-rich dipolarophiles was accomplished with a high stereo-selectivity by using an axially chiral dicarboxylic catalyst (40)." The metal-free silicon Lewis-acid-catalysed 3-1-2-cycloadditions of A-acylhydrazones with cyclopentadiene provides a mild access to pyrazolidine derivatives in excellent... 

A. Compound 72 is drawn in 73 in its most stable chair conformation, with the bulkier C02H groups equatorial and the smaller F axial. The name is wj.v-5-fUiorocyclohexane-r-l,c7j-3-dicar-boxylic acid or 5[3-fluorocyclohexane-lot,3a-dicarboxylic acid. A plane of symmetry through C 2) and C 5) of 72 rules out chirality. 

Enantiomer-differentiating hydrolysis with pig liver esterase has, as with other hydrolases, become an important method for resolution (Table 11.1-5). Kinetic resolution of oxirane mono- and dicarboxylic acid esters with pig liver esterase proceeds effeciently with good selectivities, as demonstrated in the cases 14 and 15. Resolution is of course not restricted to enantiomers with central chirality. Axial and planar chiral racemic ester have been resolved with moderate to good results with pig liver esterase (33-36). 

Figure 7.5 Axially chiral C2-symmetric dicarboxylic acids.

A three-component Ugi-type reaction using A/ -alkylbenzohydrazide (instead of amine) has been catalysed by an axially chiral binaphthyl dicarboxylic acid and found to proceed with up to 93% ee with an acyclic azomethine imine. Stereoselectivity of a Ugi reaction starting from an oxanorbornenone / -amino acid, R CHO, and RNC has been improved through solvent selection. ... 

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