Overcoming Strain-Induced Rearrangement Reactions: A Mild Dehydrative Aromatization Protocol for Synthesis of Highly Distorted p-Phenylenes

J Am Chem Soc. 2016 Mar 9;138(9):3235-40. doi: 10.1021/jacs.6b00538. Epub 2016 Feb 24.

Abstract

A series of p-terphenyl-based macrocycles, containing highly distorted p-phenylene units, have been synthesized. Biaryl bonds of the nonplanar p-terphenyl nuclei were constructed in the absence of Pd-catalyzed or Ni-mediated cross-coupling reactions, using 1,4-diketones as surrogates to strained arene units. A streamlined synthetic protocol for the synthesis of 1,4-diketo macrocycles has been developed, using only 2.5 mol % of the Hoveyda-Grubbs second-generation catalyst in both metathesis and transfer hydrogenation reactions. Under protic acid-mediated dehydrative aromatization conditions, the central and most strained benzene ring of the p-terphenyl systems was susceptible to rearrangement reactions. To overcome this, a dehydrative aromatization protocol using the Burgess reagent was developed. Under these conditions, no strain-induced rearrangement reactions occur, delivering p-phenylene units with up to 28.4 kcal/mol strain energy and deformation angles that sum up to 40°.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.