Lithiation of carbamates followed by borylation provides a powerful method for the homologation of boron reagents. However, when applied to hindered systems (secondary carbamates with tBu-boronic esters) for the construction of two quaternary centers, this methodology fails. Instead, using mixed boranes (tBuBMe2), the synthesis of adjacent quaternary stereogenic centers with full stereocontrol was successful. The process can be repeated two or three times in one pot leading to carbon chains bearing multiple contiguous quaternary stereogenic centers. The boranes were converted into tertiary alcohols or C-tertiary amines using chloramine. The origin of the high selectivity for alkyl over Me group migration was determined computationally.
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V.Aggarwal@bristol.ac.ukReceived Date (will be automatically inserted after manuscript is accepted)
ABSTRACTThe synthesis of highly enantioenriched α-heterocyclic tertiary alcohols has been achieved via lithiation-borylation of a configurationally-stable lithiated carbamate and heterocyclic pinacol boronic esters followed by oxidation. Protodeboronation of the α-heterocyclic tertiary boronic esters using TBAF.3H2O or CsF gave highly enantioenriched 1-pyridyl-1-arylethanes in high er
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