<MultiModal>![OCC(C)C(C(C)C(C(C)C[C@@H](C)[C@@H](O)CO[Si](C)(C)C(C)(C)C)=O)=O>[CSA],[CCl_4],[MeOH]>[$\mathbf{A}$],$\mathbf{A}$ is the reaction product](/media/uploads/6b7a45fc-1409-4454-9599-9770e3498d70.png)</MultiModal>

This condensation reaction produces a 6,6-spirocyclic product. Disregarding enantiomers, based on the stability of stereoconformations, please provide the most favored conformation of the condensation reaction product $\mathbf{A}$.
<MultiModal>![OCC(C)C(C(C)C(C(C)C[C@@H](C)[C@@H](O)CO[Si](C)(C)C(C)(C)C)=O)=O>[CSA],[CCl_4],[MeOH]>[$\mathbf{A}$],$\mathbf{A}$是反应产物](/media/uploads/6b7a45fc-1409-4454-9599-9770e3498d70.png)</MultiModal>

该缩合反应产生了一个6,6-螺环产物，在不考虑对映异构的情况下，根据立体构象的稳定性，请给出缩合反应产物$\mathbf{A}$的最优势构象
All other options are incorrect
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/70d68fd7-d7e8-48ba-8f85-1af733b984c5.png)</MultiModal>
<MultiModal>![C[C@H]1[C@H](CO)O[C@@](OC[C@@H](C)C2=O)([C@@H]2C)[C@@H](C)C1](/media/uploads/db9f098c-af22-41d6-829d-f4f2b644b393.png)</MultiModal>
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/959e02e6-7959-4de5-8644-008fa3bc6ae6.png)</MultiModal>
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@H](C)C1](/media/uploads/4c068749-143a-4843-b58e-65a57fc1d873.png)</MultiModal>
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@H](C)C2=O)(OC[C@@H]2C)[C@H](C)C1](/media/uploads/248d0620-4fd0-4902-99c4-f69b6fd6c8fb.png)</MultiModal>
其他选项均不正确
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/70d68fd7-d7e8-48ba-8f85-1af733b984c5.png)</MultiModal>


<MultiModal>![C[C@H]1[C@H](CO)O[C@@](OC[C@@H](C)C2=O)([C@@H]2C)[C@@H](C)C1](/media/uploads/db9f098c-af22-41d6-829d-f4f2b644b393.png)</MultiModal>
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/959e02e6-7959-4de5-8644-008fa3bc6ae6.png)</MultiModal>


<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@H](C)C1](/media/uploads/4c068749-143a-4843-b58e-65a57fc1d873.png)</MultiModal>
<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@H](C)C2=O)(OC[C@@H]2C)[C@H](C)C1](/media/uploads/248d0620-4fd0-4902-99c4-f69b6fd6c8fb.png)</MultiModal>
First, according to the prompt, the product $\mathbf{A}$ is a 6,6-spiro product, and a ketal structure is formed after condensation.

In the first chair-like six-membered ring, it is obvious that the methyl group is most stable when it is on the equatorial bond. Therefore, the configuration shown in the figure can be formed, in which two methyl groups and the hydroxymethyl group are all on the equatorial bonds. The configuration of the other spiro ring needs further discussion.

<MultiModal>![C[C@H]1[C@H](CO)O[C@]2([X2]CCC[X1]2)[C@@H](C)C1](/media/uploads/a4d33800-b796-4fb3-a5a2-8832ac682e6e.png)</MultiModal>

<Checkpoint>[In the first chair-like six-membered ring, it is obvious that the methyl group is most stable when it is on the equatorial bond](1)</Checkpoint>

Next, determine the relative position of O. We mark the axial and equatorial bonds at the spiro position as $\mathrm{X_1}$ and $\mathrm{X_2}$ respectively. Obviously, due to the anomeric effect, O is more inclined to be in the $\mathrm{X_1}$ axial bond position.

<MultiModal>![C[C@H]1[C@H](CO)O[C@]2([X2]CCC[X1]2)[C@@H](C)C1](/media/uploads/a4d33800-b796-4fb3-a5a2-8832ac682e6e.png)</MultiModal>

<Checkpoint>[Due to the anomeric effect, O is more inclined to be in the axial bond position](1)</Checkpoint>

Therefore, the position of the methyl group on the first carbon connected by the equatorial bond needs further discussion. We mark the two axial and equatorial bonds connected to the carbon at $\mathrm{X_2}$ as $\mathrm{X_3}$ and $\mathrm{X_4}$ respectively, as shown in the figure:

<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@]([X4])([X3])C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/607ff6de-bb67-4e95-a7c1-f6a91a2e23fc.png)</MultiModal>

For the methyl group close to the center of the ketal structure, being in the $\mathrm{X_4}$ equatorial bond position will generate a very large repulsive force with the methyl group on the other ring. Therefore, the methyl group preferentially occupies the $\mathrm{X_3}$ axial bond position.

<Checkpoint>[For the methyl group close to the center of the ketal structure, being in the $\mathrm{X_4}$ equatorial bond position will generate a very large repulsive force with the methyl group on the other ring. Therefore, the methyl group preferentially occupies the $\mathrm{X_3}$ axial bond position.](1)</Checkpoint>

Finally, there is also a methyl group next to the carbonyl group. Since it extends outside the ring, in the absence of other interference, the methyl group will be more stable on the equatorial bond.

<Checkpoint>[The last methyl group will be more stable on the equatorial bond](1)</Checkpoint>

<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/70d68fd7-d7e8-48ba-8f85-1af733b984c5.png)</MultiModal>

<Checkpoint>[The most stable conformation of the product: C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](1)</Checkpoint>
首先根据题干提示可知，产物$\mathbf{A}$是6,6-螺环产物，缩合后形成缩酮结构

在第一个椅式六元环中，显然甲基处于平伏键上时最稳定，因此可以形成如图所示的构型，其中两个甲基和羟甲基均处于平伏键，另一个螺环的构型需要进一步讨论。

<MultiModal>![C[C@H]1[C@H](CO)O[C@]2([X2]CCC[X1]2)[C@@H](C)C1](/media/uploads/a4d33800-b796-4fb3-a5a2-8832ac682e6e.png)</MultiModal>


<Checkpoint>[在第一个椅式六元环中，显然甲基处于平伏键上时最稳定](1)</Checkpoint>

接着确定O的相对位置，我们将螺环位置的直立键和平伏键分别标记为$\mathrm{X_1}$和$\mathrm{X_2}$，显然由于异头碳效应的存在，O更倾向于处于$\mathrm{X_1}$直立键的位置。

<MultiModal>![C[C@H]1[C@H](CO)O[C@]2([X2]CCC[X1]2)[C@@H](C)C1](/media/uploads/a4d33800-b796-4fb3-a5a2-8832ac682e6e.png)</MultiModal>

<Checkpoint>[由于异头碳效应的存在，O更倾向于处于直立键的位置](1)</Checkpoint>

因此平伏键连接的第一个碳上甲基的位置需要进一步讨论，我们将$\mathrm{X_2}$这个碳连接的两个直立键和平伏键分别标记为$\mathrm{X_3}$和$\mathrm{X_4}$，如图所示：

<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@]([X4])([X3])C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/607ff6de-bb67-4e95-a7c1-f6a91a2e23fc.png)</MultiModal>

对于靠近缩酮结构中心的甲基，处于$\mathrm{X_4}$平伏键的位置会与另一个环上的甲基产生非常大的排斥作用，因此该甲基优先处于$\mathrm{X_3}$直立键的位置上。

<Checkpoint>[对于靠近缩酮结构中心的甲基，处于$\mathrm{X_4}$平伏键的位置会与另一个环上的甲基产生非常大的排斥作用，因此该甲基优先处于$\mathrm{X_3}$直立键的位置上。](1)</Checkpoint>

最后还有一个羰基旁的甲基，由于延伸至环外，没有其他干扰的情况下，甲基处于平伏键上会更加稳定

<Checkpoint>[最后一个甲基处于平伏键上会更加稳定](1)</Checkpoint>

<MultiModal>![C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](/media/uploads/70d68fd7-d7e8-48ba-8f85-1af733b984c5.png)</MultiModal>

<Checkpoint>[产物最稳定构象：C[C@H]1[C@H](CO)O[C@@]([C@@H](C)C2=O)(OC[C@@H]2C)[C@@H](C)C1](1)</Checkpoint>