Ultrasound-assisted synthesis of RO- and RS-substituted (hetero)acenes via oxo- and thio-Friedel-Crafts/Bradsher reactions

Piotr Bałczewski; Emilia Kowalska; Joanna Skalik; Marek Koprowski; Krzysztof Owsianik; Ewa Różycka-Sokołowska

doi:10.1016/j.ultsonch.2019.104640

Ultrasound-assisted synthesis of RO- and RS-substituted (hetero)acenes via oxo- and thio-Friedel-Crafts/Bradsher reactions

Ultrason Sonochem. 2019 Nov:58:104640. doi: 10.1016/j.ultsonch.2019.104640. Epub 2019 Jun 14.

Authors

Piotr Bałczewski¹, Emilia Kowalska², Joanna Skalik³, Marek Koprowski⁴, Krzysztof Owsianik⁵, Ewa Różycka-Sokołowska⁶

Affiliations

¹ Division of Organic Chemistry, Group of Functional Materials Synthesis, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland; Faculty of Mathematics and Natural Sciences, Institute of Chemistry, Health and Food Sciences, Department of Material & Structural Chemistry, Jan Długosz University in Częstochowa, Armii Krajowej 13/15, 42-201 Częstochowa, Poland. Electronic address: pbalczew@cbmm.lodz.pl.
² Division of Organic Chemistry, Group of Functional Materials Synthesis, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland. Electronic address: kowalska@cbmm.lodz.pl.
³ Division of Organic Chemistry, Group of Functional Materials Synthesis, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland. Electronic address: jskalik@cbmm.lodz.pl.
⁴ Division of Organic Chemistry, Group of Functional Materials Synthesis, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland. Electronic address: mkopr@cbmm.lodz.
⁵ Division of Organic Chemistry, Group of Functional Materials Synthesis, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland. Electronic address: owsianik@cbmm.lodz.pl.
⁶ Faculty of Mathematics and Natural Sciences, Institute of Chemistry, Health and Food Sciences, Department of Material & Structural Chemistry, Jan Długosz University in Częstochowa, Armii Krajowej 13/15, 42-201 Częstochowa, Poland. Electronic address: e.sokolowska@ajd.czest.pl.

PMID: 31450342
DOI: 10.1016/j.ultsonch.2019.104640

Abstract

Two heteroatom-variants of the Friedel-Crafts/Bradsher cyclization of o-acetalaryl(aryl)methyl ethers and o-dithioacetalaryl(aryl)methyl thioethers, have been realized with the ultrasound assistance. The environmentally friendly "oxo-variant" (Oxo-F-C/B), proceeding in a medium containing mineral acid and a large amount of water (HCl_aq/CH₃CN) led to a very efficient formation of RO-substituted (hetero)acenes in less than 5 min. In the "thio-variant" (Thio-F-C/B), o-dithioacetalaryl(aryl)methyl thioethers underwent ultrasound-assisted cyclization in nonaqueous medium (FeCl₃/KI/EtOH) in less than 25 min., in lower yields than in the "oxygen variant" to give RS-substituted (hetero)acenes. The RO-(hetero)acenes cyclized at 25-60 °C in aqueous media but did not cyclize in organic solvents while the RS-(hetero)acenes required higher temperatures 55-60 °C and cyclized in organic solvents but did not react in aqueous media. The acceleration of the ultrasound-assisted reactions compared to the reactions carried out under silent conditions exceeded 7500 times in the most effective example of the oxo-variant and on average 2 times for the thio-variant. The plausible reaction mechanisms under ultrasound and silent conditions have been proposed. The ultrasonic mechanism involves disturbing of solvation layers and formation of the reactive ("naked") carbocations upon operation of the shock wave produced by the bubble collapse. The o-acetalaryl(aryl)methyl ethers underwent a selective ultrasound-assisted deacetalization to give o-formylaryl(aryl)methyl ethers, without subsequent cyclization under the acidic reaction conditions.

Keywords: Acenes; Cyclization; Deacetalization; Electrophilic aromatic substitution; Oxo- and thio-Friedel-Crafts/Bradsher reactions; Ultrasounds.