Sparteine chiral additive with

Thus the product in such cases can exist as two pairs of enantiomers. In a di-astereoselective process, one of the two pairs is formed exclusively or predominantly as a racemic mixture. Many such examples have been reported. In many of these cases, both the enolate and substrate can exist as (Z) or (E) isomers. With enolates derived from ketones or carboxylic esters, (E) enolates gave the syn pair of enantiomers (p. 146), while (Z) enolates gave the anti pair. Addition of chiral additives to the reaction, such as proline derivatives, or (—)-sparteine lead to product formation with good-to-excellent asynunetric induction. Ultrasound has also been used to promote asymmetric Michael reactions. Intramolecular versions of Michael addition are well known. ... 

When chiral additives such as ( —)-sparteine has added to the initial reaction with the organolithium reagent, quenching with CO2 produces carboxylic acids with good asymmetric induction. 

The aim in the previous sections was to generate chiral carbanions with enantiomeric excess by the interaction of (—)-sparteine (11) during the deprotonation. The addition of... 

TMEDA or sparteine) and transmetallation with CuCN 2LiCl, providing the adduct 51 with 90% yield. Enantioselective 1,4-additions of chiral, non-racemic a-aminoalkylcuprates (formed from the corresponding stannyl-carbamates by transmetallation, or by enantioselective deprotonation) have also been described recently.45,45a-45c... 

Another approach to enantiomerically pure planar chiral azaferrocenes involves 2-lithiation of (367) followed by addition of (-)-menthyl-(5 ) — jo-toluenesulfinate. The diastereomeric sulfoxides thus obtained are chromatograph-ically separable, and treatment of each diastereomer with t-BuLi produces an enantiomerically pure planar chiral anion that may be trapped with an electrophile (Scheme 98). Finally, in order to obviate the need for performing a resolution or a chromatographic separation, chiral ligand-mediated enantioselective deprotonations have been investigated. Lithiation of (367) in the presence of (-)-sparteine followed by addition of an electrophile gives the 2-substituted azaferrocene in good enantioselectivities (Scheme 99). However, lateral lithiation of (370) mediated by 5-valine-derived bis(oxazoline) (371) provides planar chiral products with excellent enantios-electivity. 

Katsuki and co-workers have investigated asymmetric epoxidation reactions mediated by achiral Mn(salen) complexes in the presence of chiral additives the combination of tetramethyl diamine-derived complex 37 and (—)-sparteine 38 can mediate the oxidation of chromenes with up to 73% ee (Table 2, entry 1) however, the yields were low <1997T9541>. More successful was ethylene diamine-derived complex 39, which promoted the asymmetric epoxidation of several chromenes in good to excellent yields and good levels of ee in combination with chiral... 

Primary alcohols RCH2OH can be directly oxidized to acyl fluorides RCOF with cesium fluoroxysulfate. Lactones can be prepared by oxidizing diols in which at least one OH is primary, and addition of a chiral additive, such as sparteine, leads to lactones with high asymmetric induction. 2-(3-Hydroxypropyl)anihne was oxidized to an acyl derivative that cyclized to give a lactam when heated with a rhodium catalyst. ... 

This transformation has been extended recently by the development of methods for the enantiotopos selective lithiation of a prochiral 2-butenylcarbamate and the subsequent formation of chiral 2-butenyltitanium reagents from these species (Scheme 10-94) [180]. The reaction of -2-butenylcarbamate 279 with a solution of 5ec -butyllithium and (-)-sparteine generates a crystalline lithium complex 280-sparteine. Upon addition of 4 equivalents of Ti(Oi-Pr)4, a homogeneous titanium complex 283 (see below) is formed. The titanium reagent is then allowed to react with aldehydes to produce diastereomerically pure homoallylic alcohols 282 with good to high enantioselectivity. The high enantioselectivity observed in the... 

A first attempt towards an asymmetric synthesis by the lithiation reaction used (— )-spartein as a chiral additive [12,13], but the enantioselectivity was disappointing. With the chiral (S)-M-ferrocenylmethyl-2-methylpiperidine, a high diastereoselec-tivity was observed [12, 13, 112] (note that the polemic about the structure of the product is due to different stereochemical nomenclature, i.e., central vs. planar , as discussed in Sect. 4.1). A breakthrough was achieved by the readily resolvable... 

Related chemistry has been reported by Snieckus using ferrocene-carboxamides with sparteine as additive, giving planar chiral adducts in excellent ees (up to 99%) [62]. 

Since benzyUithium compounds having no adjacent heteroatom are configurationally labile [93], their enantioselective reactions may proceed through an asymmetric substitution pathway. In 1971, Nozaki and coworkers commented in the first enantioselective reaction of benzyllithiiun compounds that the enantiomeric ratio of organolithium compounds might be influenced by a chiral additive [94]. Deprotonation of ethylbenzene was performed with n-BuLi-(-)-sparteine at 70°C, followed by carboxylation at -65°C [Eq. (39)]. 

An asymmetric synthesis of the carbon—sulfur[7]helicene 42 makes use of (—)-sparteine as a chiral additive (2009ACIE5954, 2005JA13806). The reaction sequence consists of a double deprotonation of racemic bis(p-trithio-phene) 44 with LDA in the presence of the chiral additive followed by quenching of the dilithiated species with bis(phenylsulphonyl)sulfide to give the carbon—sulfur[7]heHcene 42 (Scheme 24). 

With racemic methylthiirane, the stereoelectivity ratio r obtained with the ZnEt2/R( ) DMBD system modified with chiral additives such as (S) 2-methylbbutyl disulfide, (R) 1,2-dimethoxy 3,3-dimethyl butane and sparteine of good optical purities, is practically the same for all additives and equal to 4, i.e. almost the double of that obtained for unmodified initiator (49). In limonene, as chiral medium, r depends on the relative enantiomeric composition of the limonene used. It was found that the variation of r versus the composition II of(+) limonene pas-... 

The stannanes (-)-ent-12 and ( + )-ent- 3 (R = CH3) are obtained with >80% ee from the alkenyllithium (-)-sparteine complex105,107a (Section 1.3.3.3.1.1.). Hence, their titanium(IV) chloride mediated carbonyl additions are accompanied by chirality transfer and enantioface selection of opposite sense. This was demonstrated for the reaction with (5)-2-benzyloxy-propanal107b the d.r. (88 12) roughly reflects the enantiomeric composition of the stannanes. 

Crimmins and co-workers have developed (V-acyloxazolidinethiones as chiral auxiliaries. These reagents show excellent 2,3-syn diastereoselectivity and enantio-selectivity in additions to aldehydes. The titanium enolates are prepared using TiCl4, with (-)-sparteine being a particularly effective base.141... 

Methods for the enantioselective synthesis of 3-substituted indolines by means of the asymmetric intramolecular carbolithiation of 2-bromo-A,-allylanilines in the presence of (-)-sparteine were reported simultaneously by Bailey <00JA6787> and Groth <00JA6789>. Thus, addition of 89 to 2.2 equiv of /BuLi in the presence of the chiral ligand generates the lithium intermediate 90 which upon quenching with methanol affords the chiral indoline 91 in a process that is highly solvent dependent. 

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