Achieving High Ortho Selectivity in Aniline C-H Borylations by Modifying Boron Substituents

作者：Smith Milton R III^*; Bisht Ranjana; Haldar Chabush; Pandey Gajanan; Dannatt Jonathan E; Ghaffari Behnaz; Maleczka Robert E Jr^*; Chattopadhyay Buddhadeb^*

来源：ACS Catalysis, 2018, 8(7): 6216-6223.

DOI：10.1021/acscatal.8b00641

• C-H activation
• hydrogen bonding
• computational chemistry
• aniline
• ortho functionalization

High ortho selectivity for Ir-catalyzed C-H borylations (CHBs) of anilines results when B(2)eg(2) (eg = ethylene glycolate) is used as the borylating reagent in lieu of B(2)pin(2), which is known to give isomeric mixtures with anilines lacking a blocking group at the 4-position. With this modification, high selectivities and good yields are now possible for various anilines, including those with groups at the 2- and 3-positions. Experiments indicate that ArylN(H)Beg species are generated prior to CHB and support the improved ortho selectivity relative to B2pin2 reactions arising from smaller Beg ligands on the Ir catalyst. The lowest-energy transition states (TSs) from density functional theory computational analyses have N-H center dot center dot center dot O hydrogen bonding interactions between PhN(H)Beg and O atoms in Beg ligands. Ir-catalyzed CHB of PhN(H)Me with B(2)eg(2) is also highly ortho-selective. H-1 NMR experiments show that N-borylation fully generates PhN(Me)Beg prior to CHB. The TS with the lowest Gibbs energy was the ortho TS, in which the Beg unit is oriented anti to the bipyridine ligand.

• 出版日期2018-7