[hblondie26]

Compound 5 (I have attached it in the attachments) can be prepared either by reacting an organometallic reagent with an aromatic nitrile, or by reacting a different organometallic reagent with an aromatic carboxylic acid (assume appropriate work up.)


(a) Which aromatic compound and organometallic reagent would you use in each of the preparations described above?

I have whittled it down to the following 2 possibilities -

C6H5CN + C5H10MgBr

C6H5COOH + C5H10Li

Please can you advise if I am on the right track or do I need to split the carbon and hydrogens to show the structure ie:
 
(CH₃3)₂2CCHCH₂2MgBr 

[Dan]

The molecule in your attached document is this:



I assume what you meant was this?

[hblondie26]

Yes I did mean the molecule you put up I thought that that is what I uploaded. Sorry.

On that basis are my workings out correct?

[opsomath]

That lithium reagent will simply react with the acid.

[hblondie26]

How about this

(CH₃)₂CCHCH₂Li and C₆H₅COOH

[discodermolide]

All that will happen there is you will get the lithium salt of the acid and the corresponding alkane from the organometallic bit.
Perhaps it may be worth considering an acid derivative?

[hblondie26]

Do you mean something like LiAlH4? Lithium aluminium hydride.

So (CH3)2CCHCH2LiAlH4 us the aromatic carboxylic acid?

[discodermolide]

No I mean an acid derivative which will react with an organometallic reagent to give a ketone.
Not an aluminium hydride.

[hblondie26]

Sorry, I am confused my question says an aromatic carboxylic acid , so do you mean I should choose a different type of carboxylic acid - not use the C6H5COOH ? 

[discodermolide]

No you make a derivative of benzoic acid which will react with an organometallic reagent to give a ketone.

[opsomath]

I was actually confused by the question as I don't think there's a common reagent which goes directly from carboxylic acid -> ketone, although actually Grignards will do this with the carboxylate (a little known fact). So I guess they want you to prepare the ester as Disco suggested? The way the question was worded, it sounded like you had to use the acid.

[hblondie26]

I think that that is where I am confused as well as I think my tutor wants me to use the carboxylic acid directly - I will clarify with her and then let to know my answer. Thank you for th help so far - back to the drawing board for me this morning !

[orgopete]

Use the nitrile. It resists adding a second lithium reagent. Hydrolysis of the imine intermediate gives a ketone. This is just one method that could work, assuming this reaction was covered in your class.

[opsomath]

I thought the original question part II required a carboxylic acid (nitrile was the part I).

[hblondie26]

The question is actually in 2 parts - first one is asking for the aromatic nitrile plus OM reagent and then the 2nd part is asking for an aromatic carboxylic acid plus OMreagent to be used - both ending up with the same molecule.

I don't know what acid derivative to use unless you do something like

C6H5CH3COOH

WIth the nitrile I have used MgBr