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 viny-lene 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 iso-meric 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.