Asymmetric induction with sparteine

It should be noted that the sense of asymmetric induction in the lithiation/ rearrangement of aziridines 274, 276, and 279 by treatment with s-butyllithium/ (-)-sparteine is opposite to that observed for the corresponding epoxides (i.e. removal of the proton occurs at the (S)-stereocenter) [102], If one accepts the proposed model to explain the selective abstraction of the proton at the (R) -stereo-center of an epoxide (Figure 5.1), then, from the large difference in steric bulk (and Lewis basicity) between an oxygen atom and a tosyl-protected nitrogen atom, it is obvious that this model cannot be applied to the analogous aziridines. 

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. 

Carbolithiation of terminal dienes such as 11 is promoted by (-)-sparteine 10, irrespective of any asymmetric induction which may result. With sparteine, organolithiums even add to dienols such as 12.15... 

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. ... 

Beak and Du [1007] performed the asymmetric alkylation of racemic dipole-stabilized dilithium reagents generated by benzylic metalation of 5.2 (X = H or n-BujSn) with s-BuLi (Figure 5.2). Sparteine 2.5 must be added to anionic species prior to the electrophile. These reactions are run in THF/fert-butyl methyl ether at -78°C. No asymmetric induction is observed when this experimental procedure is used for the alkylation of 4.2. 

Cyclopropanone acetals with a quaternary carbon atom in chiral form can be established by addition of bisoxazoline-ligated allylzinc reagents to the cyclopropenes.The t-BuLi/(-)-sparteine combination favors Br-Li exchange and also promotes enantioselection in the intramolecular addition of aryllithium to an o-alkenyl side chain (e.g., indoline synthe-j.ijj) I28.I29 Moderate asymmetric induction is shown in the hydroarylation of norbomene in the presence of 63. 

The chemistry is a development of earlier methodology. [17] The organolithium additions to A-aryl imines 18, are promoted by C2-symmetric bisoxazoline (BOX) ligands, [18] e.g. 20, or (-)-sparteine [19] 21 (Scheme 4) with high asymmetric induction. 

Comparison of diether 14 and (-)-sparteine 2 reveal that they are complementary to each other, with 14 giving the best levels of asymmetric induction (up to 93 % ee) for phenyl- and vinyllithium, whilst (-)-sparteine gives the best results for butyl- and ethyllithium [26]. 

Kinetic resolution was shown by Kunieda and coworker to be another enantioselective process of a-sulfinyl carbanions. Slight asymmetric induction was achieved in the reaction of racemic a-lithiomethyl p-tolyl sulfoxide with ethyl carboxylates in the presence of (-)-sparteine [Eq. (17)] [62]. 

Deprotonation-protonation is an alternative choice for asymmetric induction. Deprotonation of the meso-phospholane oxide with s-BuLi-(-)-sparteine and subsequent protonation with acetic acid afforded trans-phospholane oxide with 45 % ee together with the recovered raeso-phospholane oxide (Table 8) [80]. 

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. ... 

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