Alexander Pulis - Synthesis of Enantioenriched Tertiary Boronic Esters by the Lithiation/Borylation of Secondary Alkyl Benzoates

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      Publication Details (including relevant citation   information):

      J. Am.   Chem. Soc. 2013,   135, 16054-16057

      A. P.   Pulis, D. J.   Blair, E. Torres and V. K. Aggarwal

      DOI:     10.1021/ja409100y

        Highlighted in SYNFACTS 2014, 10,   81


      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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