The authors present an interesting manuscript that describes the enantioselective synthesis of a range of thio-substituted cyclobutane esters via an asymmetric Michael addition approach. The manuscript is very well written and put together, with an infomrative introduction that clearly sets the current work in the context of the state-of-the-art. Initial optimisation in the racemic series showed that product dr varied with the base additive, with DBU giving optimal selectivity. Epimerisation is speculated to lead to the thermodynamic trans isomer, and this is consistent with the control experiment in Scheme 3 - taking a known ratio of diastereoisomer and treat with DBU under the reaction conditions to give the trans product in high dr. The scope and limitations of this process in the racemic series is completed with a huge variation in products described giving the desired products in high dr and generally good to excellent yields.The enantioselective reaction is then developed, with a range of catalysts screened and cat*8 assessed as optimal. A good scope and limitations is then developed using this process (Scheme 4) with high enantioselectivity observed. A number of derivatisations are then descibed upon the products (Scheme 5). The SI is complete and exceptionally clear - the authors should be congratulated on this. Overall this is an excellent addition to the literature and should be accepted once the very minor comment below is considered.

1. The authors speculate a retro-Michael addition process operates as part of the epimerisation scheme. While this is consistent with their observations, further proof of this could be demonstrated by a crossover experiment. If the epimerisation experiment in scheme 3 could be repeated in the presence of another thiol then scrambling of the thiols should be seen within the products. Although this may not be necessary it would add further credence to their hypothesis.

The authors have addressed the positive but critical comments from both referees of the original submission in an appropriate fashion. Suggested changes to the title, as well as further experimental product derivatisations and mechanistic experiments have been performed and these add to the quality of the manuscript. As such this manuscript should now be accepted in its current form.