Herein we report the B(3,4,5-F3H2C6)3-catalysed C3-allylation of indoles using allylic esters. 25 examples of C3-allylated products are presented in up to 97% yield. The mechanism for the reaction was explored...

The diverse applicability of diazo compounds as versatile reagents has enlarged the chemical toolbox in organic synthesis. Over the past few decades, transition metal-catalyzed diazo compound activation has ignited the classical synthetic methodology via utilizing highly reactive metal carbenoid species. Many reviews have also appeared in the literature which discloses the advantage and disadvantages of metal-catalyzed activation of the diazo compound. Recently, tris(pentafluorophenyl) borane-mediated diazo activation reactions have reconciled this research area due to the potential for mild, environmentally-friendly, metal-free, non-toxic reaction conditions, and the diverse reactivity patterns of boranes towards diazo compounds. In this review, we have discussed the reactivity of the boron-diazo precursor adduct with compounds using catalytic and stoichiometric halogenated triarylboranes and, the mechanism of N2 release from the diazo reagent. This generates the reactive carbene species as a key intermediate which can further be exploited for O−H, N−H, S‒H, and C−H insertions, azide insertion, carbonate transfer, C‒C and C=C bond forming reactions, [2+2] or [2+4] cascade cyclization reactions, annulation reactions, etc. This review is classified by the following themes: 1. Introduction 2. Diazo Activation Using Stoichiometric Boranes 3. Diazo Activation Using Catalytic B(C6F5)3 4. B(C6F5)3 Catalyzed Diazo Activation Reactions 5. Conclusions

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