Question

When cyclodecane-1,6-dione is treated with sodium carbonate, the product gives a UV spectrum similar to that of 1-acetyl-2-methylcyclopentene. Propose a structure for the product, and give a mechanism for its formation.

Short answer

Aldol cyclization is theintramolecular aldol reaction in which cyclization occurs in the molecule with two carbonyl groups in it.

The trendy of forming the ring in the adol cyclization reaction follows this order:

$\mathbf{6}\mathbf{-}\mathit{m}\mathit{e}\mathit{m}\mathit{b}\mathit{e}\mathit{r}\mathit{e}\mathit{d}\mathbf{>}\mathbf{5}\mathbf{-}\underset{\overrightarrow{\mathbf{S}\mathbf{t}\mathbf{a}\mathbf{b}\mathbf{i}\mathbf{l}\mathbf{i}\mathbf{t}\mathbf{y}\mathbf{}\mathbf{o}\mathbf{f}\mathbf{}\mathbf{r}\mathbf{i}\mathbf{n}\mathbf{g}\mathbf{}}}{\mathbf{m}\mathbf{e}\mathbf{m}\mathbf{b}\mathbf{e}\mathbf{r}\mathbf{e}\mathbf{d}}\mathbf{>}\mathbf{7}\mathbf{-}\mathit{m}\mathit{e}\mathit{m}\mathit{b}\mathit{e}\mathit{r}\mathit{e}\mathit{d}$

Step-by-step solution

Aldol Cyclizations

Aldol cyclization is theintramolecular aldol reaction in which cyclization occurs in the molecule with two carbonyl groups in it.

The trendy of forming the ring in the adol cyclization reaction follows this order:

$\mathbf{6}\mathbf{-}\mathit{m}\mathit{e}\mathit{m}\mathit{b}\mathit{e}\mathit{r}\mathit{e}\mathit{d}\mathbf{>}\mathbf{5}\mathbf{-}\underset{\overrightarrow{\mathbf{S}\mathbf{t}\mathbf{a}\mathbf{b}\mathbf{i}\mathbf{l}\mathbf{i}\mathbf{t}\mathbf{y}\mathbf{}\mathbf{o}\mathbf{f}\mathbf{}\mathbf{r}\mathbf{i}\mathbf{n}\mathbf{g}\mathbf{}}}{\mathbf{m}\mathbf{e}\mathbf{m}\mathbf{b}\mathbf{e}\mathbf{r}\mathbf{e}\mathbf{d}}\mathbf{>}\mathbf{7}\mathbf{-}\mathit{m}\mathit{e}\mathit{m}\mathit{b}\mathit{e}\mathit{r}\mathit{e}\mathit{d}$

 Mechanism of formation of 2,3,5,6,7,8-hexahydroazulen-4(1H)-one

Cyclodecane-1,6-dione on reacting with base carbonate forms resonance stabilized enolate. The enolate formed attacks the electrophilic carbonyl carbon resulting in ring formation. In the last step of the reaction a proton is abstracted by a baseto give the final desired product 2,3,5,6,7,8-hexahydroazulen-4(1H)-one.

Formation of 2,3,5,6,7,8-hexahydroazulen-4(1H)-one