Hypervalent iodine-mediated oxidative alkene arylation: a thorough analysis

Abstract

A hypervalent iodine (HVI)-mediated, oxidative alkene arylation reaction has been developed. Both Koser’s reagent (PhI(OH)OTs) and (diacetoxyiodo)toluene (TolI(OAc)2) were equally viable as oxidants, which reacted with ortho-vinylbiphenyl derivatives to produce tri-, tetra-, and pentacyclic polycyclic aromatic hydrocarbons in yields up to 97%. Comparison of this stoichiometric reaction with a previously reported catalytic process showed that these protocols were largely complementary, and that they likely operate via the same general mechanistic sequence involving vinyliodonium salts decomposing into vinylene phenonium ions. Various mechanistic control experiments were conducted, which ruled out epoxides as intermediates, and which showed that E- and Z-alkene geometry in 10-substituted ortho-vinylbiphenyls had no impact on the ensuing isomeric product distributions. These experiments strongly supported the formation of E-vinyliodonium ions as initial reaction intermediates, and while the occurrence of 1,2-phenyl shift products was a common phenomenon, we concluded that alkyl substitution on the ortho-vinylbiphenyl was a requirement for this alternate pathway to occur.