Construction of Multiple, Contiguous Quaternary Stereocenters in Acyclic Molecules by Lithiation-Borylation
Watson, Charlotte G Balanta, Angelica Elford, Tim G Essafi, Stephanie Harvey, Jeremy N # Aggarwal, Varinder K # ×
American Chemical Society
Journal of the American Chemical Society vol:136 issue:50 pages:17370-17373
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) in place of boronic esters the synthesis of adjacent quaternary stereogenic centers with full stereocontrol is successful. The process can be repeated 2 or 3 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.