How can 2-indanone be prepared?

[![2-indanone](https://i.stack.imgur.com/81ePf.png)](https://i.stack.imgur.com/81ePf.png)


Would adding phosgene to *ortho*-xylene lead to the formation of 2-indanone?




If you need to start with *ortho*-xylene, then you should use fazekazs's approach. I searched through SciFinder and found that the most commonly reported synthesis of 2-indanone involves oxidation of indene using a variety of conditions. 


The following *Organic Synthesis* [prep](http://orgsyn.org/demo.aspx?prep=CV5P0647) highlights this approach, although it certainly uses some outdated methodology (distillation by aspirator vs. rotary evaporation, for example). Newer reports use a variety of oxidations, including oxone or the the Wacker process.


In this example, indene **1** is added to a mixture of formic acid and hydrogen peroxide to afford the monoformate ester of indene 1,2-diol **2**. The monoformate ester was hydrolyze with sulfuric acid to give 2-indanone **3**.


[![A synthesis of 2-indanone by oxidation of indene](https://i.stack.imgur.com/uff3P.png)](https://i.stack.imgur.com/uff3P.png) 


However, when I first saw your question, I wanted to propose a synthesis based on a [Dieckmann condensation](http://www.organic-chemistry.org/namedreactions/dieckmann-condensation.shtm) on diethyl phenylene-1,2-diacetate **4** followed by decarboxylation of the $\beta$-ketoester **5**. However, I did not find this approach in the literature, and both the diacetate ester and its parent diacid are of comparaple price to 2-indanone. 


[![synthesis of 2-indanone by a Dieckmann condensation](https://i.stack.imgur.com/jnuPv.png)](https://i.stack.imgur.com/jnuPv.png)


Another interesting idea that I did not find in the literature is a pericyclic approach based on photolysis or thermolysis of beznocyclobutene **5** in the presence of carbon monoxide. Following electrocyclic ring opening, intermediate **6** can react with CO in 4+1 cycloaddition. An isocyanide could be used instead of CO, and hydrolysis of the imine would give 2-indanone. Alternatively, there may be a transition metal species that could mediate this transformation.


[![A synthesis of 2-indnaone via pericyclic reactions](https://i.stack.imgur.com/0mdAJ.png)](https://i.stack.imgur.com/0mdAJ.png)


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If you want to start from *ortho*-xylene **1** I would recommend dibromination using *N*-bromosuccinimide to obtaining *ortho*-di(bromomethyl)benzene **2**, followed by the addition of 1,3-dithianide anion **3** (prepared from formaldehyde and 1,2-ethanedithiol followed by treatment with NaH). While formaldehyde is electrophylic, 1,3-dithiane is nucleophylic if deprotonated (eg. with NaH, forming 1,3-dithianide ion) and can attack on the bromomethyl side of the molecule to get **4**. This polarity inversion is called umpolung. A second treatment with NaH gives the cyclized product **5**. Deprotection of the thioacetal gives 2-indanone **6**. With this reversed polarity approach no phosgene is needed for the synthesis.


![a synthesis of 2-indanone from o-xylene using an umpolung approach described in the paragraph above[1]](https://i.stack.imgur.com/8d31W.png)


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