Synthesis of enantioenriched tertiary boronic esters by the lithiation/borylation of secondary alkyl benzoates.
J Am Chem Soc
; 135(43): 16054-7, 2013 Oct 30.
Article
em En
| MEDLINE
| ID: mdl-24138162
ABSTRACT
Simple, secondary 2,4,6-triisopropyl benzoates (TIB esters) and secondary dialkyl N,N-diisopropyl carbamates have been reported to be resistant to deprotonation by strong bases. We have found that the combination of sBuLi (1.6 equiv) and TMEDA (6 equiv) in CPME at -60 °C enables deprotonation of unactivated secondary dialkyl TIB esters, but not the carbamates. These carbanions were reacted with a range of neopentyl boronic esters which, after 1,2-metalate rearrangement and oxidation, gave a range of tertiary alcohols in high yield and universally high er. Further functional group transformations of the tertiary boronic esters were demonstrated (conversion to quaternary centers, C-tertiary amines) together with application of the methodology to the synthesis of the simplest unbranched hydrocarbon bearing a quaternary center, (R)-4-ethyl-4-methyloctane, validating the synthetic utility of the methodology.
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01-internacional
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MEDLINE
Idioma:
En
Ano de publicação:
2013
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Article