Magnesium-Mediated Nucleophilic Borylation of Carbonyl Electrophiles

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Abstract

The diboranate derivative, [HC{(Me)CNDipp}2Mg{pinBB(n-Bu)pin}], resulting from treatment of a β-diketiminato magnesium n-butyl derivative with the commercially available diborane, B2pin2, reacts as a source of the [Bpin] nucleophile with ketones and organic isocyanates. Reactions with benzophenone and 9-fluorenone afford products, which may be rationalized as enolate species resulting from kinetically controlled dearomatization rather than the thermodynamically preferred C-borylation of the electrophilic C═O unit provided by a previously described magnesium complex bearing a terminal [Bpin] nucleophile. The enolate derivatives react readily with further equivalents of the ketones to provide C–C coupling and tetra-alkoxyborate products via aldol condensation processes. In contrast to this divergent behavior, isocyanates with [HC{(Me)CNDipp}2Mg{pinBB(n-Bu)pin}] react like the terminal boryl species to yield the anticipated C-boryl amidate products. Although we have yet to identify the origin of this contrasting reactivity, these results indicate the potential of these systems, which are ostensibly both sources of identical [Bpin] nucleophiles, to provide divergent and highly selective access to kinetic or thermodynamic reaction products.
Original languageEnglish
Pages (from-to)4457-4464
Number of pages8
JournalOrganometallics
Volume37
Issue number23
Early online date31 Aug 2018
DOIs
Publication statusPublished - 10 Dec 2018

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

Magnesium-Mediated Nucleophilic Borylation of Carbonyl Electrophiles. / Hill, Michael; Mahon, Mary; Pecharman, Anne-Frederique; McMullin, Claire.

In: Organometallics, Vol. 37, No. 23, 10.12.2018, p. 4457-4464.

Research output: Contribution to journalArticle

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AB - The diboranate derivative, [HC{(Me)CNDipp}2Mg{pinBB(n-Bu)pin}], resulting from treatment of a β-diketiminato magnesium n-butyl derivative with the commercially available diborane, B2pin2, reacts as a source of the [Bpin] nucleophile with ketones and organic isocyanates. Reactions with benzophenone and 9-fluorenone afford products, which may be rationalized as enolate species resulting from kinetically controlled dearomatization rather than the thermodynamically preferred C-borylation of the electrophilic C═O unit provided by a previously described magnesium complex bearing a terminal [Bpin] nucleophile. The enolate derivatives react readily with further equivalents of the ketones to provide C–C coupling and tetra-alkoxyborate products via aldol condensation processes. In contrast to this divergent behavior, isocyanates with [HC{(Me)CNDipp}2Mg{pinBB(n-Bu)pin}] react like the terminal boryl species to yield the anticipated C-boryl amidate products. Although we have yet to identify the origin of this contrasting reactivity, these results indicate the potential of these systems, which are ostensibly both sources of identical [Bpin] nucleophiles, to provide divergent and highly selective access to kinetic or thermodynamic reaction products.

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