Aryl Cation Chemistry as an Emerging Versatile Tool for Metal-Free Arylations

Abstract

The development of transition-metal-free arylation procedures represents a key goal in modern organic synthesis. A green arylation can be obtained by having recourse to light as a ‘clean’ reagent in place of toxic metals. In particular, a new method based upon the photoheterolytic fragmentation of substituted aryl halides or esters, with the formation of aryl cations has recently emerged. The peculiar reactivity of these cations with carbon nucleophiles allows several straightforward photo-arylations, which compare favorably with other thermal or photochemical metal-free analogues. 1 Introduction 2 Aryl Cation Chemistry 3 Metal-Free Formation of Aryl-Carbon Bonds 3.1 Formation of Aryl-Alkyl Bonds 3.1.1 Arylation of Carbonyl Compounds 3.1.2 Formation of Aryl-Allyl Bonds 3.1.3 Formation of Other Aryl-Alkyl Bonds 3.2 Formation of Aryl-Vinyl Bonds 3.3 Formation of Aryl-Alkynyl Bonds 3.4 Formation of Aryl-Aryl Bonds 3.5 Cyanation 4 Conclusions