Intramolecular Dehydrogenative Coupling of 2,3-Diaryl Acrylic Compounds: Access to Substituted Phenanthrenes

Abstract

A simple, facile, and environmentally benign intramolecular dehydrogenative coupling of various 1,2-diarylethylenes for the synthesis of phenanthrenes in excellent yield has been described. This new methodology uses ceric ammonium nitrate (CAN) as a promoter at room temperature and has been extended to intermolecular synthesis of biaryl compounds. The electron transfer from methoxyarene to cerium leads to cationic radical formation, which further proceeds to intramolecular coupling. Preliminary mechanistic investigation by EPR spectroscopy and density functional theory calculation suggested a similar view.

Total Synthesis of Phenanthropiperidine Alkaloids by Sequential Alkylation of N,N‐Dibenzylaminoacetonitrile

“…This surprising result prompted us to examine several protocols that would hopefully form ester 8 b . We also reasoned (Scheme 5) that in the case of 7 a , the formation of a new carbon to carbon bond should be carried out according to the ionic properties of cation radical A (R=OMe), whereas in the case of ester 7 b , the radical properties of cation radical A ’ (R=H) ought to dominate [33,34] . With these considerations in mind, a new experiment was undertaken under more diluted conditions.…”

The Scholl Reaction as a Powerful Tool for Synthesis of Curved Polycyclic Aromatics

“…The best example of such dual-role reagents is FeCl 3, , which is typically dissolved in CH 3 NO 2 prior to its addition to a solution of the precursor in CH 2 Cl 2 . Besides AlCl 3 –CuCl 2 , AlCl 3 –Cu­(OTf) 2 and FeCl 3 , reagents commonly employed in Scholl reactions include MoCl 5 , , phenyliodine bis­(trifluoroacetate) (PIFA)-boron trifluoride etherate (BF 3 ·OEt 2 ), − VOF 3 (with BF 3 ·OEt 2 or CF 3 CO 2 H), and cerium­(IV) ammonium nitrate (CAN) . Recently, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) with a Brønsted acid (e.g., CH 3 SO 3 H, triflic acid, and CF 3 CO 2 H) or a Lewis acid (e.g., AlCl 3 , BF 3 ·Et 2 O, or Sc­(OTf) 3 ), which was first used by Rathore and co-workers, has become a more popular reagent for Scholl reactions.…”