The review by Maji and co-workers covers a timely and important topic of arene dearomatisation by cycloaddition. These reactions are intrinsically difficult to perform, owing to their energetically uphill nature, but photocatalysis has provided new methods for achieving this normally unfavourable reaction in useful yields. The products formed are potentially widely useful across a range of disciplines, although particularly in medicinal chemistry, where this work ties in well to current efforts to make more saturated and "three-dimensional" structures.
The review covers work that has been reported since 2016, when the last review on this topic was published. The review covers all important examples, with one exception (mentioned below) and could potentially be an excellent publication in Chemical Science. However, in its current state it is not ready for publication. The schemes are largely excellent and consistently drawn – small inconsistencies are noted below - but the text needs substantial improvement. Beyond numerous grammatical errors (too many to list), there are many overwritten sentences, logical errors and sometimes seemingly disconnected sentences make the text unfortunately quite difficult to read or understand at times. The introduction also contains far too many unexplained details and terminology that, while potentially interesting, are not fully contextualized.

I have written as detailed a list as possible of suggested corrections. I urge the authors to cross-check the rest of the manuscript to make sure that changes suggested in one instance are also made to other relevant sections, even when not explicitly mentioned. The review has the potential to be excellent (and much excellent work has already been done!!) but more attention is required on the written part of the manuscript.

General comments:
- The authors often refer to irradiation of substrate in the presence of a catalyst. In most cases, I think it makes more sense to talk about irradiation of the catalyst and an interaction with the substrate – these are the important interactions.
- The authors frequently give yields to general structures. This is not correct – please draw the correct structure out and refer to this when giving the yield. For example – "Condition A forms the cycloadduct 13.3 in 88% yield." 13.3 is a general structure and does not exist – I assume the authors mean 13.3a? Please go through the rest of the manuscript and check that this mistake is eliminated elsewhere.
- I think it is good practice to refer to general compounds in the plural eg. "cycloaddition of quinolines 13.3." Please go through and see that this is replicated elsewhere.

Abstract
- Please rewrite the first sentence. I often find myself writing like this too, but this type of overwritten idiomatic English has no place in the scientific literature - "intimately embraced garment in the historical backbone."
- Second sentence: change "stereoisomerism" for "stereochemical information"
- Please rewrite the final sentence. "Provides prospective luminescence." This is again overwritten.

Introduction
- Sentence "The cycloaddition reactions bring an extremely efficient perspective…". This doesn't make linguistic sense. Perhaps "Cycloaddition reactions bring exciting opportunities in this regard…"?
- Sentences should not begin with "And..".
- Phrases "Aromatic compounds would, in principle…" and "dearomative cycloaddition reactions can be considered..". "Would" and "can" should probably both be changed to "could." The point, presumably, is that they could be very useful, but their challenging energetics makes this generally difficult.
- Figure 1C: It might be helpful to label ET(product) and ET(PS) in the scheme
- Figure 1E: The Dexter EnT part of the scheme is extremely confusing. If you know what a Dexter energy transfer is then the scheme can be followed, but this is a tutorial review and I am not convinced that anybody would be able to learn what a Dexter energy transfer is from this scheme. I would suggest to draw this out in a line more like a reaction equation, showing the orbital occupation before and after irradiation, and after simultaneous electron transfer.
- I'm afraid I could not follow the paragraph beginning "decades of investigations…" and this should be rewritten. Frequent references are made to Figures 1A-D but I see little connection between any of the information in the text and what is in the figure. The information in the Figure is actually very good, and provides a good basis for the text – what is described in Figure 1A-C just needs to be clearly explained and discussed. 1A shows the fundamental energetic challenge of these types of reactions, 1B the first solution with direct irradiation. 1C, how photocatalysis has an impact.
- I think a more logical construction for the introduction would involve discussing Figure 1A+B, then introducing the three modes of arene-alkene cycloaddition, and then discussing the direct irradiation methods (from paragraph beginning "In 1959, Angus and Bryce-Smith…". I would then show Figure 1C and 1E, and then discuss the first examples of photocatalytic alkene-arene cycloadditions.
- Schemes showing the reactions discussed in the remainder of the introduction would be very useful!
- The paragraph beginning "In 1959, Angus and Bryce-Smith…" begins with a series of short sentences that are essentially bullet points. It is difficult to follow the ideas through to the final conclusion. Results are mentioned without discussing their significance, ideas introduced without context, "evidence" is mentioned without saying what the evidence is. The nomenclature of the energy terms (1B2u, 3B1u) is not defined anywhere. I'm afraid that for this reviewer, the statement "Weller equation clearly shows that…" is incorrect. I was not able to interpret the equation on the basis of the limited explanation provided. How does the equation show different selectivity for different deltaG?
- Sentence beginning "In this regard, an external photosensitizer (PS) bridges aromatic hydrocarbons…". The use of "bridges" is confusing. A photosensitizer allows aromatic hydrocarbons to be photochemically excited by visible light. I assume this is what was meant.
- "Given the context of dearomative cycloaddition.." should be changed to "In the context of dearomative cycloaddition.."
- "Dexter EnT described the concurrent two-electron transfer.." – please delete EnT.
- Sentence beginning "In 1950, the sensitization-induced…". The authors write "the restriction is based on low absorption" – what restriction? I don't know what the authors are trying to say here. I would also refer to unwanted rather than unexpected side products.

I would encourage the authors to include ortho or para in the section titles eg. 2. Dearomative [2+2] ortho-cycloadditions. This terminology was emphasized in the introduction but is not used in the subtitles in the rest of the manuscript.

1. Dearomative [2+2] cycloaddition
2. I would refer to the first "direct" ortho-photocycloaddition, to emphases the lack of photocatalyst/sensititzer.
3. Remove "By definition"
4. Change "Triplet sensitization is employed to promote the arene moiety" to "Triplet sensitization is employed to excite the arene moiety"

2.1 Intramolecular dearomative [2pi+2pi] cycloaddition
- Remove phrase "started the road map". Perhaps say "reported the first"?
- The second sentence is written in an illogical order. The important interaction is the catalyst being irradiated, not the substrate. The sentence structure makes it sound like a direct excitation of the substrate by 455nm LEDS, which is not true. This is frequently written – I would encourage the authors to go through the manuscript and check for this elsewhere.
- The authors then say cycloadduct 2.2 was isolated in 96% yield. This is impossible as 2.2 is a generic structure. The R groups are not defined. This is a frequent error throughout the manuscript. A range of yields could be given for a generic structure, to reflect the range of yields achieved for substrates that are consistent with the generic structure, but a single yield for an undefined structure makes no sense. Please change this, and change the part of the Figure too!
- The authors then write "PS-1 could not productively interact with 2.2". At first I was confused by this statement but then realized the authors were explaining that this ensured selectivity for products 2.2 and not the onward reactivity to 2.3. I would make this point more obvious. Sentence order is important. Perhaps state the yield of 2.2 with PS-1, then state that with PS-2, a different product 2.3 was obtained, and then use the energy levels of the substrates and catalysts to explain the difference in observed reactivity.
- The sentence "The formation of 2.3 is not the primary focus of this review and is not discussed" is not true – the mechanism is discussed later and much of the Figure 2 is devoted to it. I would leave the material in (it is interesting!) and delete the sentence.
- Rewrite sentence "Instead, the authors complemented the explicit compatibility of the PS's…". Perhaps "Instead, the authors correlated the differing product identities with the different ETs of the respective PSs."?
- Figure 2: I think the title should be "Visible light-mediated EnT dearomative…" Please change the word order in other titles.
- The authors comment on the importance of the phenyl group in 3.2b, but in example 3.2c, there is no pendant phenyl group. They mention that the N-EWG group increases the reactivity, but it would be good if the reason why (if known) could be mentioned.
- Replace "…followed by radical addition to give the desired [2+2] cycloadduct 3.2" with "…followed by radical recombination to give the desired [2+2] cycloadduct 3.2"
- Replace "…their low solubility check the widespread application of this scheme." with "…their low solubility limit the widespread application of this reaction."
- The authors describe Nolan's work as "sustainable" but it uses an expensive and rare Gold catalyst, and high energy 365 UV light. I would not describe this as sustainable.
- The triplet energy of Nolan's gold catalyst should also be mentioned in the text
- Replace "Indole with substituted EDGs was also well tolerated…" with "Indoles with electron-donating substituents were also well tolerated…"
- Replace "…and quantum yield determination prove the mechanism…" with "…and quantum yield determination provide evidence to support the mechanism…". We rarely actually "prove" a mechanism, in almost all cases all we are doing is eliminating other possible mechanisms and providing evidence that is consistent with what we propose.
- "Substrate 4.1 has a relatively higher ET that PS-2…" – the ET for 4.1 should be given
- Replace "meager yields" with "lower yields"
- "…introducing trifluoroethanol resulted in a dramatically improved yield of 4.2" – what was the yield?
- Avoid using terms like "depicted" and "registered" when introducing new publications – reported, disclosed, published, demonstrated, are all better alternatives.
- Replace "Due to conformational restrictions in the bridged ring structure, an indene-fused substrate underwent dearomative [2 + 2] cycloaddition, providing the corresponding product 4.8 with 96% yield, thus, ruling out the possibility of a 1,5-HAT process." With "Due to conformational restrictions preventing a 1,5-HAT process, an indene-fused substrate underwent dearomative [2 + 2] cycloaddition, providing product 4.8 in 96% yield."
- The authors sometimes write Kcal/mol – kcal/mol is correct.
- "…for a C3-EWG substituted substrate, PS-2 did not furnish a reasonable yield." Since this yield is not given in the scheme it would be useful to have it written here.
- Figure 4: I think descriptive titles next to the authors name and year in the scheme would be useful, perhaps replicate the names given in the figure title. Having the information immediately available is always good and saves the reader having to go hunting in a figure caption.
- I would rewrite the sentence "Vinylcyclopropanes are amongst the most vital building blocks in organic synthesis." I don't think many would agree with this statement, although they do certainly show highly interesting and unusual reactivity!
- In this section I was astonished that the fact that the cyclopropanes were present in the final product was not discussed. The authors mentioned the use of cyclopropanes as radical clocks but then didn't comment that this wasn't observed here. What implication does this have for the mechanism?
- In the discussed on Dhar's 2020 work, the numerical effect of the C2 carboxamide group on ET should be given. When the authors write "..which eliminated the requirement for the phenyl and ester group at the C2 position" I assume they are referring to the chemistry in Figure 3? If so, this should be explicitly referred to. Otherwise reference should be made to the chemistry that is being compared to.
- "A feeble amount of cycloadducts" should be changed to something like "However, only small quantities of cycloadducts.."
- Figure 5: Lightbulb is missing from mechanism in part B.
- The discussion of Koenig/Ohkuma's work has a number of issues. (1) "The desired cis-fused methylenecyclobutane-containing products…" It is not clear to me if this sentence is referring to Koenig's or Ohkuma's work. (2) none of the alkyne, deacylated, or photo-Fries products are shown. If their importance is such that they are discussed, then ideally they should also be shown in the scheme. (3) It is not clear what the "difficulties" faced by Ohkuma were.
- The ET of aryl iminium ions 6.1 and of TXT should be given in the discussion of Bach's 2022 work.
- "…do not give expected products owing to inaccessible triplet states." This is a speculative explanation from Bach's publication. The sentence as written makes it sound like an established fact.

2.2 Intermolecular [2pi+2pi] cycloaddition

• Please remove "obvious" from the first sentence.
• The discussion of Meggers' chemistry is written in very short sentences. Please try and rewrite providing a bit more structure and context, which will make it easier to read.
• I would not call Meggers' reaction stereospecific – he never used this term himself in the original publication. There is a temperature dependence to the observed selectivity (which is not stated clearly enough in this review) and he argues that the intermediate biradical is extremely short lived. The result appears similar but, in my view, this is not stereospecificity in the truest sense.
• For the work of Oderinde, 8.1d-g were "too short lived to undergo intermolecular cycloaddition reactions." Can this reactivity be correlated with the structure of the compounds? Would be useful to the reader if this were the case.
• Why does the fact that the reaction in Figure 8 can be performed with the poorly oxidizing catalyst PS-5 warrant a mention? The significance is not clear from the text.

2.3 Intermolecular [2pi+2sigma] cycloaddition

• References 67 and 68 can be added to: J. Am. Chem. Soc. 202, 144, 7988–7994, ACS Catal. 2023, 13, 7, 5096–5103.
• The authors mention that 9.3a was formed without Lewis acid having previously said that neither reaction partner absorbs at 450nm and that the Lewis acid was required (?) for the bathochromic shift. There is either something incorrect here or something is not completely explained.

3 Dearomative [4pi+2pi] cycloaddition

• There should be a scheme here. This is nice chemistry and deserves to be shown. The discussion in this section is also generally better than others.
• Final sentence – what is the focus of the next section? Arene excitation or arenophile excitation? Both as proposed as solutions to the challenge of electronically mismatched substrates, but not clear which one will then be discussed.

3.1 Intramolecular [4pi+2pi] cycloadditions

• I would avoid using the words "inert" and "unresponsive" in the first sentence. I would say the reactions are difficult. I would also emphasise that reactivity by activation of the pyridine core itself is difficult – general "pyridine derivatives" are shown to work in the next section!
• The authors mention a "remarkable >20:1 dr was observed in CH2Cl2." For which substrate? I can't find this result in the scheme.
• Reference missing and should be discussed: G. Zhen, G. Zeng, F. Wang, X. Cao, B. Yin, Adv. Synth. Catal. 2023, 365, 43–52.
• The section from "During this process, 11.5 equilibrates… …cycloadduct 11.2 was formed after radical addition" should be rewritten. At the moment it sounds like an equilibrium forms, stabilizes, and then is shifted, which cannot be the case. Perhaps "During this process, 11.5 is in equilibrium with the 1,4-biradical 11.6, which is itself removed from equilibrium by radial recombination from its resonance form 11.7."
• Figure 11: correct "open shell singlet radical". The drs of the products should also be given.
• In the discussion of Maestri's work, the authors write sentences such as "intramolecular attack of 12.5 to the naphthyl moiety" and "intermediate 12.8 attacked the benzyl arm." The moiety and arm are both part of the compounds which attack, so the sentence construction does not make sense. "Intramolecular attack of the excited allene onto the naphthyl moiety of 12.5" would be more accurate, for example.
• The authors need to be a bit clearer in connecting the "low-energy" and "high-energy" transition states to the (I assume) structures aromatized arene 12.5 and dearomatized 12.6. This wasn't immediately clear to me.
• Why is the pathway for 12.2 (presumably via aromatized 12.8) not considered "low-energy"? Perhaps again something is not clearly explained here…
• The authors then refer to an "unproductive ET" – I'm not sure this is the best description. The energy transfer itself it fine, the problem is the presence of an unwanted side reaction, I think.
• The effect of the Naphthalene additive should be quantified in the scheme for the substrates where it is relevant – no yields are currently given.

3.2 Intermolecular [4pi+2pi] cycloaddition
- In the section discussing Kano's work the authors write " It was shown that adding HCl (2 equiv.) sped up the [4 + 2] cycloaddition reaction for the less reactive 5- or 8- substituted quinolines. From these observations, the authors suspected that the acceleration of EnT might not be the exact function of acids." Either I am misunderstanding something or this is a direct contradiction? Please check this.
- The endo product "13.13" with styrene that is formed in >20:1 dr is not shown. Do the authors also mean rr here? Please check.
- In the section covering Maji's work they refer to PS-2 as an "energy harvester." It is probably better to simply refer to this as a photocatalyst.
- Please change "the reaction transpired" to "the reaction proceeded"
- Figrue 14: Sometimes the authors write endo:exo and sometimes dr - please be consistent with terminology. Compound 14.7a the dr is >20:1

4 Conclusion and outlook

• The authors write "…to compensate for entropic issues and the high reactivity of the EnT-activated substrates." Do they not mean low reactivity? High ET energies…
• The sentence "Not only the pi-system the development also includes the sigma-framework." is not a full sentence and should be rewritten. I assume the sigma framework refers to the BCBs?
• Figure 15: change Kcal/mol to kcal/mol.
• Figure 15: Although I was unsure at first, I think this scheme is actually a good idea – but perhaps put the substrates first and then the catalysts second. The information on the substrates is much more interesting and useful (the catalyst data can be otherwise found from many sources – but I would still keep it here!).
• The authors talk about designing new sensitisers with ever higher triplet energies, but surely a more interesting and widely applicable strategy is to design new ways to lower the triplet energy of existing substrates?

References:
2 – Book? Page number, publisher etc. needed DOI not needed.
27 – incomplete
30 – incomplete
38 – second page number missing
43 – page numbers missing and doi present.
47 – incomplete
48 – publisher needed, DOI to be removed
56 – second page number needed
90 – publisher needed