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

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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

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