Dimethyl 3,7-diamino-4,8-bis((2-methoxy-2-oxoethyl)thio)benzo[1,2-b:4,5-b’]dithiophene-2,6-dicarboxylate

Round 1

Reviewer 1 Report

The manuscript of Short Note: “Dimethyl 3,7-diamino-4,8-bis((2-methoxy-2-oxoethyl)thio)benzo[1,2-b:4,5-b']dithiophene-2,6-dicarboxylate” by authors: Branislav Pavilek, Daniel Vegh, Dusan Bortnak, Veronika Smejkalova, Jozef Kozisek and Viktor Milata has been properly described and the product has been fully characterized by X-Ray analysis, 1H, 13C NMR, IR spectroscopy, and microanalysis. I have only one comment. In principle the reaction should be carried out in methanol not in ethanol. The reason for this is the possible base catalyzed reesterification of the methyl ester functional group to ethyl ester, which would lead to a mixture of products. Fortunately for the authors, this side reaction proceeded very slowly under the reaction conditions described. The present manuscript should be acceptable for publication in the Molbank without further revision.

Author Response

Dear Reviewer,

thank you for your kind input to our manuscript. Your comment is justified and true. During the optimization, the reaction was carried out in a variety of solvents such as THF, MeOH, EtOH, and dimethyl carbonate. As there was negligible impact on the reaction results, we kept using the solvent most accessible for our research group. In general, it would be safer to use MeOH to avoid the creation of possible side products.

Kind regards,

Branislav Pavilek

Reviewer 2 Report

The present short note by Pavilek and coworkers describes the synthesis of Dimethyl 3,7-diamino-4,8-bis((2-methoxy-2-oxoethyl)thio)benzo[1,2-b:4,5-b']dithiophene-2,6-dicarboxylate (BDT), a material potentially usable for optoelectronics. The product has been extensively characterized by 1H-NMR, 13C-NMR, IR, elemental analysis and X-ray crystallography.

Comments:

- The main body of the article (introduction, results, discussion, conclusions) is quite sparse. This might be acceptable for a short note, but I suggest adding some more scientific background to this rather technical report.

- I suggest adding the mechanism of product formation as an additional scheme.

- In the titular compound the two (2-methoxy-2-oxoethyl)thio residues are in para position. Did you also observe the formation of the ortho isomer? If not, what could be possible reasons?

- Please add the CIF report for the X-ray structure to the supplementary materials. If it includes any serious alerts (levels A, B or C) provide appropriate responses.

- Synthesis section: In addition to the molar amounts, also add the weights and the molar equivalents of the substances to the procedure.

Author Response

Dear Reviewer,

thank you for your kind input to our manuscript. I would like to address your comments as follows:

• you are right, the main body is sparse, as we indeed aim to publish a short note. If you deem it necessary to expand the main body even though it is supposed to be a short note, please let me know.
• I added a reference for a possible mechanism pathway for a structurally similar derivative, however, in our case we did not study the mechanism, and therefore it might not be suitable for publication as it is only our suggestion with no evidence.
• We did not observe the formation of the ortho isomer. I depicted a possible explanation in the attached pdf. If aromatic substitution proceeds via SnAr, then the second SnAr of methyl 2-mercaptoacetate on chlorine must be in ortho or para position in order for BDT (linear vs angular) to be formed. We propose SnAr in the para position as the overall net activating and deactivating effect of the substituents in this stage favors SnAr on para chorine. Also, both methyl 2-mercaptoacetate moieties in the ortho position could create possible steric repulsions, and therefore this favors the creation of a para (linear) isomer as well. Please notice, the mechanism is not exhausting, and I bundled some steps together such as deprotonation/protonation, or formation/breakdown of tetrahedral intermediates. Also, the sequence of the steps may differ.
• I uploaded CIF file into supplementary materials.
• Weights and molar equivalents were added to the synthesis section.

Kind regards,

Branislav Pavilek

Author Response File: Author Response.pdf