Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross-coupling chemistry. This type of reaction has traditionally been mediated by transition-metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic pathway, which is triggered by the hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of in situ counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.

1,1-Diboryl alkenes are versatile building blocks in organic synthesis and medicinal chemistry. However, there have been only a small number of established methods to prepare this class of compounds, and most of them used transition-metal catalysts, which are undesirable in the preparation of biologically relevant compounds. Herein, we report an unprecedented application of P1– t Bu phosphazene as a superbasic organocatalyst to promote 1,1-diboration reactions of unactivated aromatic and electron-deficient terminal alkynes. The dual Brønsted and Lewis basicity of this phosphazene enables the activation of reaction substrates and allows for high regio- and stereoselectivity to be obtained. A combination of thorough experimental and computational studies suggests interesting mechanistic insights for these phosphazene-catalyzed diboration reactions, which are also discussed in detail.

A Friedländer-based method for transition-metal free, aerobic synthesis of chromene-fused quinolinones is reported.

We report a method to convert substituted tropylium ions into benzenoid derivatives.