Synthesis of N,N’-dialkyl-6,6’-dibromoisoindigo derivatives by continuous flow

Veronique Maes; Geert Pirotte; Jeroen Brebels; Pieter Verstappen; Laurence Lutsen; Dirk Vanderzande; Wouter Maes

doi:10.1556/1846.2015.00033

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Journal of Flow Chemistry

Volume/Issue:: Volume 5: Issue 4

Synthesis of N,N’-dialkyl-6,6’-dibromoisoindigo derivatives by continuous flow

Authors:

Veronique Maes

Veronique Maes Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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Geert Pirotte

Geert Pirotte Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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Jeroen Brebels

Jeroen Brebels Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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Pieter Verstappen

Pieter Verstappen Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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Laurence Lutsen

Laurence Lutsen Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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Dirk Vanderzande

Dirk Vanderzande Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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, and

Wouter Maes

Wouter Maes Hasselt University, Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
IMEC-IMOMEC, Universitaire Campus, Wetenschapspark 1, 3590 Diepenbeek, Belgium

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wouter.maes@uhasselt.be

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Pages:: 201–209

Online Publication Date:: Dec 2015

Publication Date:: 01 Dec 2015

Article Category:: Research Article

DOI:: https://doi.org/10.1556/1846.2015.00033

Keywords:: isoindigo; N-alkylation; condensation; reduction; asymmetric substitution; organic photovoltaics

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In this work, the synthesis of N,N’-dialkyl-6,6’-dibromoisoindigo derivatives by continuous-flow chemistry is explored as a means to enhance material availability and structural diversity, in particular toward the application of isoindigo-based semiconductors in high-performance organic photovoltaic devices. The individual steps in the conventional batch synthesis protocol are evaluated and, when needed, adapted to flow reactors. To overcome the low solubility of non-alkylated 6,6’-dibromoisoindigo in common organic solvents, the flow condensation reaction between the 6-bromo-isatin and 6-bromo-oxindole precursors is evaluated in polar aprotic solvents. Dialkylation of 6,6’-dibromoisoindigo is readily performed in flow using a solid-phase reactor packed with potassium carbonate. In an alternative strategy, solubility is ensured by first introducing the N-alkyl side chains on 6-bromo-isatin and 6-bromo-oxindole (accessible via a high-yielding flow reduction of alkylated 6-bromo-isatin), followed by condensation using the conventional method in acetic—hydrochloric acid medium. The N,N’-dialkylated 6,6’-dibromoisoindigo derivatives indeed show enhanced solubility in the hot reaction mixture compared to the non-alkylated material but eventually precipitate when the reaction mixture is cooled down. Nevertheless, the condensation between both alkylated starting materials is achieved in flow without any blockages by keeping the outlet from the reactor heated and as short as possible. The latter strategy allows the preparation of both symmetrically and asymmetrically N-substituted isoindigo compounds.

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Journal of Flow Chemistry A Journal of the Flow Chemistry Society

Print ISSN:: 2062-249X

Online ISSN:: 2063-0212

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Journal of Flow Chemistry
Language	English
Size	A4
Year of Foundation	2011
Volumes per Year	1
Issues per Year	4
Founder	Áramlásos Kémiai Tudományos Társaság
Founder's Address	H-1031 Budapest, Hungary Záhony utca 7.
Publisher	Akadémiai Kiadó Springer Nature Switzerland AG
Publisher's Address	H-1117 Budapest, Hungary 1516 Budapest, PO Box 245. CH-6330 Cham, Switzerland Gewerbestrasse 11
Responsible Publisher	Chief Executive Officer, Akadémiai Kiadó
ISSN	2062-249X (Print)
ISSN	2063-0212 (Online)