Reaction Scheme

Below, IR spectra for this sequence are provided:

IR Spectra

For compound E, I suggest the formation of a conjugated ester with the elimination of $\ce{-OH}$ group. The IR peak at $\pu{1732 cm-1}$ is a reasonable value for $\ce{C=O}$ stretch of ester.

Subsequently for F, I suggest the presence of a hydroxyl group due to the strong peak at $\pu{3400 cm-1}$. The reformation of hydroxyl group from $\ce{C=C}$ is unlikely due to the conjugated system. Plus, hydrolysis of ester will give broad $\ce{-OH}$ peak which is unlikely from the spectrum. Hence, I am inclined to suggest vinylogue Michael addition of compound D to yield compound F. However, I am hesitant because of the possibility of dehydration.

For compound G, I would like to suggest the presence of alkyne yet the peak is strong. Possibly, would it be $\ce{CO2}$? If decarboxylation occurs, compound F must be β-keto-acid which is generated after hydrolysis of ester. The nucleophilic attack from compound D would also attack the carbonyl group instead of the $\ce{C=C}$ bond of compound E.

Compound Suggestion
E Text
F Text
F' Text
F'' Text

Possibly, my reasoning is wrong at the first place. I am confused currently. Any suggestion is really appreciated.

After reading the suggestion, I consider the potential of O-nucleophile. Reversible acidic hydrolysis of ester, E can form acrylic acid. Then, it will form acrylic anhydride. The conjugated system might lower the C=O stretch to lower frequency. Is this plausible? Is the condition suitable for the formation of acid anhydride without phosphorous pentoxide? However, I am still clueless for compound G.

  • 1
    $\begingroup$ consider the possibility of lactone formation $\endgroup$
    – Waylander
    Feb 6, 2022 at 8:19
  • 1
    $\begingroup$ The suggest of the metharcylate E makes sense given the reaction conditions and comparison of the IR spectrum given to you with an experimental spectrum by AIST/SDBS (entry SDBS 1220). Does the original question really truncate provision of the conditions/reagents for $\ce{E -> F -> G}$? Or, does it state that $\ce{D -> G}$ proceeds by telescoping/a one-pot procedure? $\endgroup$
    – Buttonwood
    Feb 6, 2022 at 11:47
  • $\begingroup$ @Buttonwood The original question only states that this is a multistep reaction sequence. I am unsure about the possibility of one-pot procedure. However, only conditions/reagents are shown for the first step. I believe the subsequent steps will follow the similar conditions. $\endgroup$
    – user4723
    Feb 6, 2022 at 12:36
  • 1
    $\begingroup$ @Waylander Except for cropping the header, replacing English transmittance and wavenumber by Chinese, this is copying the work by AIST/SDBS (entry 1220 mentioned earlier) without proper credit where (to whom) is credit is due. $\endgroup$
    – Buttonwood
    Feb 6, 2022 at 15:02


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