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Spontaneous Resolution and Carbonation of Chiral Benzyllithium Complexes
Author(s) -
Lennartson Anders,
Sundberg Jonas,
Wiklund Tove,
Hilmersson Göran,
Håkansson Mikael
Publication year - 2010
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200901172
Subject(s) - chemistry , enantiomer , carbonation , crystallization , crystallography , selectivity , stereochemistry , medicinal chemistry , organic chemistry , catalysis
In search for new examples of absolute asymmetric synthesis (AAS), chiral α‐substituted benzyllithium complexes have been prepared. While [Li(phet)(pmdta)] ( 1 ) (phet = 1‐phenylethyl, pmdta = N , N , N′ , N″ , N″ ‐pentamethyldiethylenetriamine) affords only racemic crystals, a promising candidate for AAS was indeed found: [Li(phet)(tmpda)], α‐ 2 , (tmpda = N , N , N′ , N′ ‐tetramethylpropylenediamine) crystallises as a conglomerate. Although concomitant polymorphism was not observed, a racemic phase (β‐ 2 ) could also be isolated. Chiral crystals of α‐ 2 gave 2‐phenylpropionic acid in high yield on reaction with gaseous CO 2 , but the bulk product was racemic. It is unclear whether the lack of selectivity originates during crystallisation or carbonation. In order to investigate this, similar complexes displaying Si or S atoms in the α‐position were prepared and structurally characterized: [Li(tmsb)(tmpda)] (tmsb = 1‐trimetylsilylbenzyl) ( 3 ), [Li{C(CH 3 )(Ph)(SPh)}(pmdta)] ( 4 ), [Li{C(CH 3 )(Ph)(SPh)}(tmeda)] ( 5 ), and [Li(tmeda) 2 ][C(CH 3 )(Ph)(SPh)] ( 6 ). The introduction of heavy atoms should allow determination of absolute configuration and enantiopurity, but so far only racemic crystals have been obtained.