In this manuscript, Zhu and co-workers disclosed a noteworthy study on the deuterocarboxylation of alkynes with oxalate and D2O in a photocatalytic approach. The key to this catalytic photoredox-neutral strategy is to generate intermediate deuterated cinnamic acid derivatives through sequential radical addition/single electron transfer (SET) and D2O deuteration, followed by two rounds of SET/deuteration to obtain the final product. The Stern-Volmer quenching analysis confirmed that the excited state of 4DPAIPN triggers a reaction through reduction quenching. In general, considering the importance of the work, this manuscript is suitable for publication in Chem. Sci. after mirror revision.
1) Please give an explanation why the yield is relatively lower of 2l and 3a in comparison with other products. What’s the main byproduct?
2) Did the author obtain the product of CO2•− addition to the indole double bond with 1m and 1n as substrates? Can acetylene be dicarboxylated under N2 atmosphere?
3) Why the yield is relatively lower in table 1, entry 4?
4) Can the author obtain alkynyl carboxylic acid under standard reaction conditions?
5) Regarding the reaction mechanism, under the condition of cinnamic acid derivatives as intermediates, it is necessary to determine whether the excited state photocatalyst reacts with oxalate first or with cinnamic acid derivatives first. Please cite literatures or provide experimental evidence to support this.
6) Refs 2b, 14b, 14c and 14e should be cited or mentioned in Ref 15.

In this manuscript, Zhu and colleagues presented a significant investigation on the deuterocarboxylation of alkynes using oxalate and D2O in a photocatalytic method. The central aspect of this catalytic photoredox-neutral approach involves the formation of intermediate deuterated cinnamic acid derivatives via sequential radical addition/single electron transfer (SET) and D2O deuteration, followed by two cycles of SET/deuteration to yield the final product. The Stern-Volmer quenching analysis validated that the excited state of 4DPAIPN initiates the reaction through reduction quenching. Given the significance of the research and the authors' effective response to previous review feedback, this manuscript is deemed suitable for publication in Chem. Sci.