Chiral diamine salts

Their previous screening of catalysts for of aldol reactions and Robinson annu-lations suggested the possibility that chiral amines might also be able to catalyze the Mannich reaction [30, 31]. Thus, screening of catalysts for Mannich-type reactions between N-OMP-protected aldimines and acetone revealed that chiral diamine salt 10, L-proline 11, and 5,5-dimethylthiazolidine-4-carboxylic acid (DMTC) 12 are catalysts of Mannich-type reactions affording Mannich adducts in moderate yields with 60-88 % ee. To extend the Mannich-type reactions to aliphatic imines, the DMTC 12-catalyzed reactions are performed as one-pot three-component procedures. The o-anisidine component has to be exchanged with p-anisidine for the one-pot reactions to occur. The DMTC 12-catalyzed one-pot three-component direct asymmetric Mannich reactions provide Mannich adducts in moderate yield with 50-86 % ee. 

These catalysts included chiral diamine salt 10 and l-5,5-dimethylthiazoIidine-4-carboxylic acid (DMTC) 12. It is noteworthy that the Mannich-type reactions were also extended to aliphatic imines. In this case, the DMTC 12-catalyzed reactions were performed as one-pot three-component procedures. 

The general term Salen-type is used in literature to describe the class of [O, N, N, O] tetradentate bis-Schiff base ligands. Some of the salen ligands 167,168 and 169 and their metal complexes are illustrated in Fig. 9.9. Commercial synthesis of chiral Salen complex 171, from chiral diamine salt 172 and salicylaldehyde derivative 173 is presented in Scheme 9.45 [83]. 

Scheme 38.6 Chiral diamine salt catalyzed exo-selective Diels-Alder reactions.

In 2003, Sigman et al. reported the use of a chiral carbene ligand in conjunction with the chiral base (-)-sparteine in the palladium(II) catalyzed oxidative kinetic resolution of secondary alcohols [26]. The dimeric palladium complexes 51a-b used in this reaction were obtained in two steps from N,N -diaryl chiral imidazolinium salts derived from (S, S) or (R,R) diphenylethane diamine (Scheme 28). The carbenes were generated by deprotonation of the salts with t-BuOK in THF and reacted in situ with dimeric palladium al-lyl chloride. The intermediate NHC - Pd(allyl)Cl complexes 52 are air-stable and were isolated in 92-95% yield after silica gel chromatography. Two diaster corners in a ratio of approximately 2 1 are present in solution (CDCI3). 

The reaction of an orf/io-ester, e.g., HC(OEt)3, with a secondary bisamine in the presence of an anunonium salt yields imidazolidinium salts (Scheme The necessary secondary diamines can be generated by a classical condensation-reduction sequence or by applying the palladium-catalyzed Buchwald-Hartwig amination." The latter reaction offers convenient access to imidazolidinium salts with chiral backbones starting from chiral diamines, a number of which are commercially available. ... 

The simpler architecture is the 1,1 -biphenyl scaffold, likewise introduced by Hoveyda and coworkers [19]. The synthesis of the imidazolium salt starts with a chiral diamine and a substituted, achiral biphenyl [82-84], Subsequent introduction of a Mes substituent on the remaining primary amino end and ring closure reaction yields the chiral saturated imidazolium salt after hydrolysation of the methoxy group to liberate the phenolic hydroxy group (see Figure 4.22). Reaction with silver(I) oxide and carbene transfer to a Grubbs (Hoveyda) catalyst sets up the ruthenium catalyst complex. 

Clavier et al. used the amino acid (L)-valine to synthesise a C-chiral imdazolidinium salt for chiral molecular recognition studies [65]. The synthetic route utilises the C-terminus to form an amide. Subsequent reduction to the diamine and ring closure with trimethyl-orthoformate yields the chiral imdazolidinium salt (see Figure 6.25). 

Optically active imidazolines are generally obtained from enantiopure 1,2-diamines. For example, chiral ferro-cenylimidazolines are prepared from ferrocenyl carboxylic acid 1241 (Scheme 310). Amide 1242 is activated by 0-alkylation with Et30 BF4, generating iminium ether tetrafluoroborate salt 1243. The formation of the imidazoline ring in 1244 is accomplished by condensation of 1243 with the chiral diamine 1245 at room temperature without the need to isolate the intermediate imidate 1243 <20050L4137>. 

With chiral diamine 24, in the form of a trifluoroacetate salt, the classic aqueous biphasic protocol has been successfully applied to the asymmetric Michael reaction of ketones with both aryl and alkyl nitroolefins. Brine is used as the aqueous phase. ... 

Asymmetric aldol reaction of silyl enol ethers. (16,221-222). The use of TiCI4 as promoter of aldol condensation of silyl enol ethers with aldehydes, first reported in 1973 (6,590-591), has seen wide use, but has the drawbacks that 1 cquiv. of the Lewis acid is required and that an asymmetric version requires use of chiral aldehydes or chiral silyl enol ethers. More recently, the combination of a salt and a weak Lewis acid, neither effective catalysts themselves, was found to be effective in catalytic (5-10 mol %) amounts. Further research showed that tin(ll) triflatc when coordinated with a chiral diamine can effect catalytic asymmetric allylation of aldehydes (13,302) and Michael reactions (15,313-314), even though this complex cannot promote aldol condensation. Eventually the combination of tin(Il) triflatc, a chiral diamine,... 

The importance of the combination of chiral diamine-coordinated tin(II) triflate and tributyltin fluoride is obvious from the result that no enantiomeric selection was observed when using only chiral diamine-coordinated tin(II) triflate or a combination with other metal salts. Tributyltin fluoride was found to be the most effective among the several tin(IV) fluorides examined. The maximum ee was obtained (92%) when (S)-l-methyl-2[(iV-l-naphthylamino)methyl]pyrro-lidine (19) was employed as the chiral diamine. 

Li and co-workers [129] developed the first enantioselective organocatalytic direct vinylogous Michael addition of y-butenolides 130 to chalcones catalyzed by the vicinal primary-diamine salt 56 (Scheme 5.64). The reaction proceeded smoothly to afford the highly valuable chiral y-butenolides 131 with good yields and high... 

The group of Lai and Rafii prepared a chiral imidazolium tetrafluoroborate from commercially available (lR,2R)-l,2-diamlnocyclohexane (Scheme 2.167) [61]. Palladium-catalyzed coupling of the diamine and mesityl bromide with 3 equiv of NaOtBu produced a diamine in the first step. Cyclization of this material with triethyl orthoformate in the presence of ammonium tetrafluoroborate led to the chiral BF, salt in an almost quantitative yield [62]. Finally, the chiral rhodium complex was synthesized by reacting the ligand precursor with an equimolar amount of potassium hexamethyldisilazide, followed by coordination to rhodium with [RhCl(COD)]2. 

Tricyclic derivatives, such as (96), of diaza-12-crown-4 form inclusion complexes with suitable guest ammoniimi salts. Some structural selectivity is shown for example diamine salts H3N(CH2) NH3 with n = 5 or 6 give the strongest complexes with (96), presumably by host recognition of a best fit in its cavity. In a study of complexes of chiral diaza-crown ethers such as (97) with chiral... 

In 2001, after screening several chiral diamines and protonic acid additives, Yamamoto and coworkers reported that a TfOH salt of 22 could efficiently promote asymmetric aldol reactions [117]. Thereafter, similar studies using chiral diamines such as 22-24 with Brnnsted or Lewis acid additives have also been reported [118-122]. In 2006, the Mase/Takabe/Barbas groups discovered that prohnamine catalyst 25 with a HpophUic side chain showed efficient catalytic activity in water (Scheme 1.5) [123]. Thus, cyclohexanone reacts smoothly with various aldehydes in water to afford the desired aldol products in high yields with excellent diastereo-... 

SNl-type reactions 747 chiral triazoUum salts 497,1113 chiral vidnal diamines 311 chiral xanthone 1114... 

The simple primary-tertiary diamine salts can be successfully applied in the aldol reactions of a-hydroxyketones with good activity and excellent stereoselectivity. Notably, the catalyst enabled the reaction of dihydroxyacetone (DHA), a versatile C3-building block in the chemical and enzymatic synthesis of carbonhydrates. By employing either free or protected DHA, syn- or anh-diols could be selectively formed with excellent enantioselectivity (Scheme 5.7). Since enantiomers of diamine 26 and 29 are readily available, this class of chiral primary amine catalysts thus functionally mimics four types of DHA aldolases in nature [17b]. Later, simple chiral primary-tertiary diamine 27 derived from amino acid was also found to be a viable catalyst for the iyn-selective aldol reactions of hydroxyacetone and free DHA (Scheme 5.7) [18]. 

Benzophenone, although an achiral molecule, has been shown to exist in two different enantiomeric forms in the solid state [39]. Mikami s and Ding s groups [40] independently reported the use of achiral benzophenone-based bisphosphine hgands in combination with enantiopure chiral diamines to generate Noyori-type Ru(II) catalysts for the asymmetric hydrogenation of ketones. A library of Ru(II) catalysts was set up by combining the achiral benzophenone-based bisphosphines 25a-d (Scheme 5.14) and enantiopure 1,2-diamines 21a-i with the Ru salt. 

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