Formal [4 + 1] cycloadditions of ketiminoboranes and isonitriles

Abstract

A formal [4 + 1] cycloaddition of ketiminoboranes with various isonitriles was developed. Ketiminoboranes were formed by a reaction sequence of hydroboration of a commercially available 1,3-diene with HB(C₆F₅)₂ followed by allylboration of a variety of nitriles. The mechanism involved in situ generated BN-dienes from ketiminoboranes via intramolecular proton transfer, which was supported by deuterium labelling experiments. Additionally, this reaction can be viewed as a catalyst-free multicomponent reaction providing an efficient approach for synthesizing unsaturated BN-heterocycles via the hydroboration/allylboration/[4 + 1] cycloaddition reaction sequence. These results are attractive complements for the [4 + 1] cycloaddition reaction and open up new opportunities for the formation of unsaturated BN-heterocycles beyond traditional five-membered rings.