Formation of Nucleophilic Allylboranes from Molecular Hydrogen and Allenes Catalyzed by a Pyridonate Borane that Displays Frustrated Lewis Pair Reactivity.

Max Hasenbeck,Urs Gellrich,Arthur Averdunk,Sebastian Ahles,Jonathan Becker

doi:10.1002/anie.202011790

Max Hasenbeck, Urs Gellrich + Show 3 more

Open Access

https://doi.org/10.1002/anie.202011790

Copy DOI

Abstract

Here we report the in situ generation of nucleophilic allylboranes from H2 and allenes mediated by a pyridonate borane that displays frustrated‐Lewis‐pair reactivity. Experimental and computational mechanistic investigations reveal that upon H2 activation, the covalently bound pyridonate substituent becomes a datively bound pyridone ligand. Dissociation of the formed pyridone borane complex liberates Piers borane and enables a hydroboration of the allene. The allylboranes generated in this way are reactive towards nitriles. A catalytic protocol for the formation of allylboranes from H2 and allenes and the allylation of nitriles has been devised. This catalytic reaction is a conceptually new way to use molecular H2 in organic synthesis.

Highlights

We report the in situ generation of nucleophilic allylboranes from H2 and allenes mediated by a pyridonate borane that displays frustrated-Lewis-pair reactivity
We recently reported reversible H2 activation by the pyridonate borane 3 that can be described as an intramolecular frustrated Lewis pair (FLP).[7,8,9]
In the stage of this research project, we aimed to examine if the allylboranes generated in this way could be used as nucleophiles for an allylation reaction

Summary

Introduction

We report the in situ generation of nucleophilic allylboranes from H2 and allenes mediated by a pyridonate borane that displays frustrated-Lewis-pair reactivity. Allylboranes are a prevalent class of C-nucleophiles.[1,2,3] Classic ways for their preparation include the addition of nucleophilic allyl Grignard or allyl lithium compounds to electrophilic boron methoxides.[4] already in 1977 Kramer and Brown reported the formation of nucleophilic allylboranes upon hydroboration of allenes by 9-borabicyclo[3.3.1]nonane (9-BBN, 1) (Scheme 1).[5] The allylborane 2 prepared in this way was used in the first total synthesis of Brevianamide A, a highly challenging target for organic synthesis, reported earlier this year. We recently reported reversible H2 activation by the pyridonate borane 3 that can be described as an intramolecular frustrated Lewis pair (FLP).[7,8,9] A distinguishing feature of this system is that the H2 activation is associated

Objectives

Results

Conclusion