Generation of a configurationally stable, enantioenriched α-oxy-α-methylbenzyllithium: Stereodivergence of its electrophilic substitution

Highly Enantioselective Reaction of α-Lithio 2-Quinolyl Sulfide Using Chiral Bis(oxazoline)s: A New Synthesis of Enantioenriched Thiols

“…The reaction of carbanions with carbonyl compounds generally proceeds through coordination to the lithium ion to give the product with retention of the configuration of the carbanion. [14] Obviously, this is not the case here. The coordination of the nitrogen of the quinolyl group prevents the approach of an electrophile to the carbanion from the side of the lithium ion, while it allows the approach from the side opposite the carbanion-lithium bond.…”

The Mechanism of the Stereospecific Intramolecular Arylation of Lithiated Ureas: The Role of Li+ Probed by Electronic Structure Calculations, and by NMR and IR Spectroscopy

“…[3][4][5][6] Such an approach fails when the two substituents flanking the ketone or imine are sterically and electronically similar, and in these cases stereospecific construction of the quaternary centre from a pre-existing tertiary centre is an appealing alternative. Carbamate derivatives 1 of benzylic secondary amines [7,8] or alcohols [9,10] may be deprotonated to give configurationally stable lithio derivatives 2, which react with electrophiles either with retention or inversion, [11] allowing the formation of quaternary centres in the products 3 (Scheme 1). [12,13] Aggarwal et al have extended the utility of the lithiated carbamates of secondary benzylic alcohols by showing that they may be transformed into tertiary alcohols and amines 4 through the addition and rearrangement chemistry of boron derivatives.…”

“…However, the rearrangements of ureas and carbamates differ from one another in one very important respect: the aryl migration within the urea proceeds with retention of stereochemistry at the migration terminus, [15] whereas the aryl migration within the carbamate proceeds with inversion of stereochemistry at the migration terminus. [18] Chiral benzyllithium derivatives are known to react with electrophiles with erratic stereospecificity (retentive S E 2ret or invertive S E 2inv), [10][11][12] and while the detailed stereochemical pathways by which such stereospecific electrophilic substitution reactions proceed are yet to be fully clarified, it is generally clear that Lewis base electrophiles capable of coordination to lithium favour retentive over invertive substitution. [12] Scheme 1.…”

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

“…The deprotonation of N-Boc-piperidine (159), giving substituted piperidines such as 160, proceeds with much lower efficiency (equation 36) 115,116 . The main side reaction is the attack of s-BuLi at the Boc-group.…”

“…Only few types of benzyllithium compounds being configurationally stable in solution at −78 • C are known: lithium-TMEDA complexes of secondary O-benzyl N,N-dialkyl carbamates, such as 211 159 or the 2,4,6-triisopropylbenzoate 212 160,161 , of secondary Naryl-N-Boc-benzylamines (213) and the dilithio-(−)-sparteine derivative 214 162 .…”