View in EDS

Mechanistic Studies into Amine-Mediated Electrophilic Arene Borylation and Its Application in MIDA Boronate Synthesis.

Saved in:

Bibliographic Details
Title:	Mechanistic Studies into Amine-Mediated Electrophilic Arene Borylation and Its Application in MIDA Boronate Synthesis.
Authors:	Bagutski, Viktor¹, Del Grosso, Alessandro¹, Carrillo, Josue Ayuso¹, Cade, Ian A.¹, Helm, Matthew D.¹, Lawson, James R.¹, Singleton, Paul J.¹, Solomon, Sophia A.¹, Marcelli, Tommaso² tommaso.marcelli@chem.polimi.it, Ingleson, Michael J.¹ michael.ingleson@manchester.ac.uk
Source:	Journal of the American Chemical Society. 1/9/2013, Vol. 135 Issue 1, p474-487. 14p.
Subjects:	Electrophilic addition reactions, Boronic acids, Aromatic compounds, Amines, Imino compounds, Acetic acid derivatives
Abstract:	Direct electrophilic borylation using Y2BCl (Y2 = Cl2 or o-catecholato) with equimolar AlCl3 and a tertiary amine has been applied to a wide range of arenes and heteroarenes. In situ functionalization of the ArBCl2 products is possible with TMS2MIDA, to afford bench-stable and easily isolable MIDA-boronates in moderate to good yields. According to a combined experimental and computational study, the borylation of activated arenes at 20 °C proceeds through an SEAr mechanism with borenium cations, [Y2B(amine)]+, the key electrophiles. For catecholato-borocations, two amine dependent reaction pathways were identified: (i) With [CatB(NEt3)]+, an additional base is necessary to accomplish rapid borylation by deprotonation of the borylated arenium cation (s complex), which otherwise would rather decompose to the starting materials than liberate the free amine to effect deprotonation. Apart from amines, the additional base may also be the arene itself when it is sufficiently basic (e.g., N-Me-indole). (ii) When the amine component of the borocation is less nucleophilic (e.g., 2,6-lutidine), no additional base is required due to more facile amine dissociation from the boron center in the borylated arenium cation intermediate. Borenium cations do not borylate poorly activated arenes (e.g., toluene) even at high temperatures; instead, the key electrophile in this case involves the product from interaction of AlCl3 with Y2BCl. When an extremely bulky amine is used, borylation again does not proceed via a borenium cation; instead, a number of mechanisms are feasible including via a boron electrophile generated by coordination of AlCl3 to Y2BCl, or by initial (heteroarene)AlCl3 adduct formation followed by deprotonation and transmetalation. [ABSTRACT FROM AUTHOR]
	Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database:	Engineering Source

Description
Abstract:	Direct electrophilic borylation using Y2BCl (Y2 = Cl2 or o-catecholato) with equimolar AlCl3 and a tertiary amine has been applied to a wide range of arenes and heteroarenes. In situ functionalization of the ArBCl2 products is possible with TMS2MIDA, to afford bench-stable and easily isolable MIDA-boronates in moderate to good yields. According to a combined experimental and computational study, the borylation of activated arenes at 20 °C proceeds through an SEAr mechanism with borenium cations, [Y2B(amine)]+, the key electrophiles. For catecholato-borocations, two amine dependent reaction pathways were identified: (i) With [CatB(NEt3)]+, an additional base is necessary to accomplish rapid borylation by deprotonation of the borylated arenium cation (s complex), which otherwise would rather decompose to the starting materials than liberate the free amine to effect deprotonation. Apart from amines, the additional base may also be the arene itself when it is sufficiently basic (e.g., N-Me-indole). (ii) When the amine component of the borocation is less nucleophilic (e.g., 2,6-lutidine), no additional base is required due to more facile amine dissociation from the boron center in the borylated arenium cation intermediate. Borenium cations do not borylate poorly activated arenes (e.g., toluene) even at high temperatures; instead, the key electrophile in this case involves the product from interaction of AlCl3 with Y2BCl. When an extremely bulky amine is used, borylation again does not proceed via a borenium cation; instead, a number of mechanisms are feasible including via a boron electrophile generated by coordination of AlCl3 to Y2BCl, or by initial (heteroarene)AlCl3 adduct formation followed by deprotonation and transmetalation. [ABSTRACT FROM AUTHOR]
ISSN:	00027863
DOI:	10.1021/ja3100963