Rearrangement reactions are quite common in synthesis:

<MultiModal>![The image shows a multi-step reaction: CC1=CC=C2C(C3C=CC2(C(OC)=O)C3)=C1OC>C[Si](C)(N=[N+]=[N-])C>[A]>O=C(OC(C)=O)C.CC(O)=O>[B], where A and B are compound codes](/media/uploads/da1b0617-3152-466a-bffe-9f2aabdb753e.png)</MultiModal>

From $\mathrm{A}$ to $\mathrm{B}$, the reaction proceeds through one neutral intermediate $\mathrm{X}$ and three positively charged intermediates, sequentially denoted as $\mathrm{Y_1}$, $\mathrm{Y_2}$, and $\mathrm{Y_3}$. Based on the above information, select the correct answer.
合成中的重排反应十分常见：

<MultiModal>![图片中为多步反应：CC1=CC=C2C(C3C=CC2(C(OC)=O)C3)=C1OC>C[Si](C)(N=[N+]=[N-])C>[A]>O=C(OC(C)=O)C.CC(O)=O>[B]，其中A和B均为化合物代号](/media/uploads/da1b0617-3152-466a-bffe-9f2aabdb753e.png)</MultiModal>

从$\mathrm{A}$到$\mathrm{B}$一共经历了一个不带电荷的中间体$\mathrm{X}$，和3个带一个正电荷的中间体，依次为$\mathrm{Y_1}$、$\mathrm{Y_2}$、$\mathrm{Y_3}$。根据以上信息，选出正确答案。
The structure of $\mathrm{A}$ is <MultiModal>![CC1=CC=C2C(C3C(NN=N4)C4C2(C(OC)=O)C3)=C1OC](/media/uploads/8d5ecaff-f637-4f54-815d-7d44df08b90a.png)</MultiModal>
During the reaction, no carbon-carbon single bond cleavage occurs.
The structure of $\mathrm{X}$ is <MultiModal>![CC1=CC=C2C(C3C4C(N4C(C)=O)C2(C(OC)=O)C3)=C1OC](/media/uploads/e3da6470-8bf8-4d1d-b784-2adcaa4b9951.png)</MultiModal>
The structure of $\mathrm{B}$ is <MultiModal>![CC1=CC=C2C(C3CCC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/7492948c-40d7-427d-a808-e248884a4f48.png)</MultiModal>
<MultiModal>![CC(O)=O](/media/uploads/79d09d68-8516-4868-bc34-26f15eee1874.png)</MultiModal> only acted as an acid catalyst during the reaction.
The structure of the intermediate $\mathrm{Y_1}$ is <MultiModal>![CC1=CC=C2C(C3C(NC(C)=O)[CH+]C2(C(OC)=O)C3)=C1OC](/media/uploads/4e87ec36-9527-4f4b-a408-45251e8b3da6.png)</MultiModal>
$\mathrm{A}$的结构为<MultiModal>![CC1=CC=C2C(C3C(NN=N4)C4C2(C(OC)=O)C3)=C1OC](/media/uploads/8d5ecaff-f637-4f54-815d-7d44df08b90a.png)</MultiModal>
反应过程中没有发生碳-碳单键断裂
$\mathrm{X}$的结构为<MultiModal>![CC1=CC=C2C(C3C4C(N4C(C)=O)C2(C(OC)=O)C3)=C1OC](/media/uploads/e3da6470-8bf8-4d1d-b784-2adcaa4b9951.png)</MultiModal>
$\mathrm{B}$的结构为<MultiModal>![CC1=CC=C2C(C3CCC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/7492948c-40d7-427d-a808-e248884a4f48.png)</MultiModal>
<MultiModal>![CC(O)=O](/media/uploads/79d09d68-8516-4868-bc34-26f15eee1874.png)</MultiModal>在反应过程中仅起到了酸催化的作用
中间体$\mathrm{Y_1}$的结构为<MultiModal>![CC1=CC=C2C(C3C(NC(C)=O)[CH+]C2(C(OC)=O)C3)=C1OC](/media/uploads/4e87ec36-9527-4f4b-a408-45251e8b3da6.png)</MultiModal>
<MultiModal>![C[Si](C)(N=[N+]=[N-])C](/media/uploads/384bdb7d-22d9-4171-bd8e-8a1527b21db5.png)</MultiModal>

The main reactivity characteristics are: serving as a source of the azido group (nucleophilic azidation), acting as a 1,3-dipole for [3+2] cycloaddition to form triazoles, decomposing under specific conditions to generate nitrenes for insertion or addition reactions, and having a nitrogen-silicon bond that is prone to hydrolysis or acidolysis, facilitating desilylation.

<Checkpoint>[<MultiModal>![C[Si](C)(N=[N+]=[N-])C](/media/uploads/384bdb7d-22d9-4171-bd8e-8a1527b21db5.png)</MultiModal> may exhibit reactivity characteristics leading to aziridine formation](1)</Checkpoint>

Reaction type: This is a [3+2] cycloaddition reaction (also known as Huisgen cycloaddition) between a 1,3-dipole and an alkene. Trimethylsilyl azide acts as the 1,3-dipole, while the non-aromatic double bond in the starting material serves as the dipolarophile. Reaction regioselectivity: The reaction will occur at the non-aromatic double bond in the starting material.

<Checkpoint>[The reaction will occur at the non-aromatic double bond in the starting material](1)</Checkpoint>

Aromatic double bonds (in the benzene ring moiety) exhibit high stability and typically do not participate in such cycloaddition reactions.

The formed N-H triazole, especially when fused within a highly strained polycyclic system, is highly prone to decomposition through nitrogen elimination.

<Checkpoint>[The formed N-H triazole, especially when fused within a highly strained polycyclic system, is highly prone to decomposition through nitrogen elimination.<MultiModal>![CC1=CC=C2C(=C1OC)C3CC2(C4C3N4)C(=O)OC](/media/uploads/ec83914e-075e-4399-a81f-c52cb401f104.png)</MultiModal>](1)</Checkpoint>

This process usually generates highly reactive intermediates (such as nitrenes or through concerted processes), followed by skeletal rearrangement. For such fused bicyclic triazoles, common rearrangement outcomes include ring contraction to form a smaller ring (e.g., a cyclopropane ring) or more complex skeletal rearrangements to release ring strain. This corresponds to product $\mathrm{A}$.

After nitrogen elimination and rearrangement, an amino group is generated, which is immediately acetylated by acetic anhydride (a strong acetylating agent) to form an amide structure.

<Checkpoint>[An amino group is generated, which is immediately acetylated by acetic anhydride (a strong acetylating agent) to form an amide structure.](1)</Checkpoint>

Considering the ring-opening and rearrangement tendencies of aziridines and the acetylating effect of acetic anhydride, product $\mathrm{B}$ will be a ring-opened and rearranged compound containing an acetamido group (derived from the nitrogen of the aziridine). The specific rearrangement pathway depends on the direction of ring strain release and electronic effects.

Possible ring-opening modes: Aziridine ring-opening can occur along either the N-C bond or the C-C bond.

If ring-opening occurs along the N-C bond, it may form an alkene and an imine.

If C-C bond cleavage is involved, more complex rearrangements may occur. The N-C bond has greater polarity and is more prone to ring-opening under acidic conditions, thus forming intermediate $\mathrm{Y_1}$.

<MultiModal>![CC1=CC=C2C(C3[CH+]C(NC(C)=O)C2(C(OC)=O)C3)=C1OC](/media/uploads/e49c5b34-cc34-4bc3-bd2f-b0b88debb958.png)</MultiModal>

<Checkpoint>[The N-C bond has greater polarity and is more prone to ring-opening under acidic conditions, thus forming intermediate $\mathrm{Y_1}$  <MultiModal>![CC1=CC=C2C(C3[CH+]C(NC(C)=O)C2(C(OC)=O)C3)=C1OC](/media/uploads/e49c5b34-cc34-4bc3-bd2f-b0b88debb958.png)</MultiModal>](1)</Checkpoint>

Subsequently, the strong electron-donating methoxy group can stabilize the carbocation, forming intermediate $\mathrm{Y_2}$ containing a three-membered ring.

<MultiModal>![CC1=CC=C2C3(C4C3C(NC(C)=O)C2(C(OC)=O)C4)C1=[O+]C](/media/uploads/99e5362c-e24f-454f-a9bc-e3a9b8eb20b7.png)</MultiModal>

<Checkpoint>[The strong electron-donating methoxy group can stabilize the carbocation, forming intermediate $\mathrm{Y_2}$ containing a three-membered ring  <MultiModal>![CC1=CC=C2C3(C4C3C(NC(C)=O)C2(C(OC)=O)C4)C1=[O+]C](/media/uploads/99e5362c-e24f-454f-a9bc-e3a9b8eb20b7.png)</MultiModal>](1)</Checkpoint>

This non-aromatic structure is unstable and undergoes further C-C bond cleavage to restore aromaticity.

<Checkpoint>[This non-aromatic structure is unstable and undergoes further C-C bond cleavage to restore aromaticity](1)</Checkpoint> The system now tends to form intermediate $\mathrm{Y_3}$, which is not destabilized by the electron-withdrawing inductive effect of the nitrogen atom.

<MultiModal>![CC1=CC=C2C(C3[CH+]CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/25aa3e86-6480-44e3-bb42-9e40f0ada5cb.png)</MultiModal>

<Checkpoint>[Intermediate $\mathrm{Y_3}$  <MultiModal>![CC1=CC=C2C(C3[CH+]CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/25aa3e86-6480-44e3-bb42-9e40f0ada5cb.png)</MultiModal>](1)</Checkpoint>

Finally, the carbocation is attacked by the nucleophilic acetate anion in the system to yield stable product $\mathrm{B}$.

<MultiModal>![CC1=CC=C2C(C3C(OC(C)=O)CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/a1af0d75-27d6-46be-b93c-24b5fca3e937.png)</MultiModal>

<Checkpoint>[The carbocation is attacked by the nucleophilic acetate anion in the system to yield stable product $\mathrm{B}$  <MultiModal>![CC1=CC=C2C(C3C(OC(C)=O)CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/a1af0d75-27d6-46be-b93c-24b5fca3e937.png)</MultiModal>](1)</Checkpoint>
<MultiModal>![C[Si](C)(N=[N+]=[N-])C](/media/uploads/384bdb7d-22d9-4171-bd8e-8a1527b21db5.png)</MultiModal>

的主要反应性特点是：作为叠氮基团的来源（亲核叠氮化）。作为 1,3-偶极体进行 [3+2] 环加成形成三唑。在特定条件下分解生成氮烯，进行插入或加成反应，其氮-硅键易于水解或酸解，方便脱硅。

<Checkpoint>[<MultiModal>![C[Si](C)(N=[N+]=[N-])C](/media/uploads/384bdb7d-22d9-4171-bd8e-8a1527b21db5.png)</MultiModal>的主要反应性特点是可能形成氮杂环丙烷](1)</Checkpoint>

反应类型： 这是1,3-偶极体与烯烃之间的 [3+2]环加成反应（也称为Huisgen环加成）。叠氮三甲基硅烷作为1,3-偶极体，起始物中的非芳香性双键作为亲偶极体。反应区域选择性： 反应将发生在起始物中的非芳香性双键上。

<Checkpoint>[反应将发生在起始物中的非芳香性双键上](1)</Checkpoint>

芳香性双键（苯环部分）具有高度的稳定性，通常不参与此类环加成反应。

形成的 N-H 三唑，尤其是当它稠合在一个张力较大的多环体系中时，非常容易通过脱除氮气而分解。

<Checkpoint>[形成的 N-H 三唑，尤其是当它稠合在一个张力较大的多环体系中时，非常容易通过脱除氮气而分解，得到产物$\mathrm{A}$<MultiModal>![CC1=CC=C2C(=C1OC)C3CC2(C4C3N4)C(=O)OC](/media/uploads/ec83914e-075e-4399-a81f-c52cb401f104.png)</MultiModal>](1)</Checkpoint>

这个过程通常会形成高度活泼的中间体（如氮烯或通过协同过程），继而发生骨架重排。对于这种稠合的双环三唑，常见的重排结果是环收缩，形成一个更小的环（例如环丙烷环），或者发生更复杂的骨架重排，以释放体系的张力。这对应产物$\mathrm{A}$

在氮气脱除和重排后，生成了氨基，乙酸酐（强乙酰化剂）会立刻对其进行乙酰化，生成酰胺结构。

<Checkpoint>[生成了氨基，乙酸酐（强乙酰化剂）会立刻对其进行乙酰化，生成酰胺结构。](1)</Checkpoint>

考虑到氮杂环丙烷的开环和重排倾向，以及乙酸酐的乙酰化作用，产物$\mathrm{B}$将是一个开环并重排的化合物，其中包含一个乙酰胺基团（来自氮杂环丙烷的氮）。具体的重排途径取决于环张力释放的方向和电子效应。

可能的开环模式： 氮杂环丙烷的开环可以沿着N-C键或C-C键进行。

如果沿着N-C键开环，可能形成烯烃和亚胺。

如果涉及到C-C键断裂，则可能会有更复杂的重排。N-C键极性更大，在酸作用下更容易开环，因此形成中间体$\mathrm{Y_1}$

<MultiModal>![CC1=CC=C2C(C3[CH+]C(NC(C)=O)C2(C(OC)=O)C3)=C1OC](/media/uploads/e49c5b34-cc34-4bc3-bd2f-b0b88debb958.png)</MultiModal>

<Checkpoint>[N-C键极性更大，在酸作用下更容易开环，因此形成中间体$\mathrm{Y_1}$  <MultiModal>![CC1=CC=C2C(C3[CH+]C(NC(C)=O)C2(C(OC)=O)C3)=C1OC](/media/uploads/e49c5b34-cc34-4bc3-bd2f-b0b88debb958.png)</MultiModal>](1)</Checkpoint>

随后，强给电子基团甲氧基可以稳定碳正离子，形成含有三元环的中间体$\mathrm{Y_2}$

<MultiModal>![CC1=CC=C2C3(C4C3C(NC(C)=O)C2(C(OC)=O)C4)C1=[O+]C](/media/uploads/99e5362c-e24f-454f-a9bc-e3a9b8eb20b7.png)</MultiModal>

<Checkpoint>[强给电子基团甲氧基可以稳定碳正离子，形成含有三元环的中间体$\mathrm{Y_2}$  <MultiModal>![CC1=CC=C2C3(C4C3C(NC(C)=O)C2(C(OC)=O)C4)C1=[O+]C](/media/uploads/99e5362c-e24f-454f-a9bc-e3a9b8eb20b7.png)</MultiModal>](1)</Checkpoint>

该非芳香性的结构并不稳定，继续发生C-C键断裂，恢复芳香性，

<Checkpoint>[该非芳香性的结构并不稳定，继续发生C-C键断裂，恢复芳香性](1)</Checkpoint>但此时倾向于形成不被氮原子吸电子诱导效应去稳定化的中间体$\mathrm{Y_3}$

<MultiModal>![CC1=CC=C2C(C3[CH+]CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/25aa3e86-6480-44e3-bb42-9e40f0ada5cb.png)</MultiModal>

<Checkpoint>[中间体$\mathrm{Y_3}$  <MultiModal>![CC1=CC=C2C(C3[CH+]CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/25aa3e86-6480-44e3-bb42-9e40f0ada5cb.png)</MultiModal>](1)</Checkpoint>

最后，碳正离子被体系中的亲核试剂乙酰负离子进攻，得到稳定产物$\mathrm{B}$

<MultiModal>![CC1=CC=C2C(C3C(OC(C)=O)CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/a1af0d75-27d6-46be-b93c-24b5fca3e937.png)</MultiModal>

<Checkpoint>[碳正离子被体系中的亲核试剂乙酰负离子进攻，得到稳定产物$\mathrm{B}$  <MultiModal>![CC1=CC=C2C(C3C(OC(C)=O)CC2(C(OC)=O)C3NC(C)=O)=C1OC](/media/uploads/a1af0d75-27d6-46be-b93c-24b5fca3e937.png)</MultiModal>](1)</Checkpoint>