title: Synthesis of enantioenriched tertiary boronic esters by the lithiation/borylation of secondary alkyl benzoates.
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.
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Pulis
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Blair
authors.forename: Eva
authors.initials: E
authors.lastname: Torres
authors.forename: Varinder K
authors.initials: VK
authors.lastname: Aggarwal