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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: phillyj on November 15, 2007, 06:46:32 PM

Title: single ring to double ring synthesis
Post by: phillyj on November 15, 2007, 06:46:32 PM

I'm having trouble with this:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg225.imageshack.us%2Fimg225%2F269%2F36633206lz4.jpg&hash=3519e22df7ff2a62577a7c897896cf60c7acf148) (http://imageshack.us)

I'm not sure of the first step. does it involve the OH group or should I try to create the second ring? I believe that the reaction does not involve the first  ring and everything occurs in the straight chain. I also think that methyl shift is involved later in the reaction but please help my start it.

Thanks

 

Title: Re: single ring to double ring synthesis
Post by: phillyj on November 15, 2007, 10:22:21 PM

can anyone please help me? i been working on this for so long and i cant get the final product.

Title: Re: single ring to double ring synthesis
Post by: Dan on November 16, 2007, 03:51:26 AM

Start by losing water, leaving a secondary carbocation. I think there's a methyl shift at this point, giving the (more stable) tertiary carbocation. You can then attack this carbocation wth the electron rich double bond, leaving another tertiary carbocation. Then pick off a proton to re-form the (most stable) tetra-substituted alkene.

Title: Re: single ring to double ring synthesis
Post by: phillyj on November 16, 2007, 09:31:42 AM

pick off a proton from what? where does the proton come from?
of an HBr or the like?

Title: Re: single ring to double ring synthesis
Post by: Dan on November 16, 2007, 01:26:46 PM

No, I mean take a proton off the intermediate. I have drawn what I meant.

Title: Re: single ring to double ring synthesis
Post by: phillyj on November 17, 2007, 02:02:40 PM

yes that looks similar to what i did. except in my method H3O+ donates a proton to the -OH producing a H2O that leaves a carbocation. then i used methyl shift and created a carbocation as your step 3 shows. then the alkene donated a proton forming the second ring. then H2O doantes an electron to the H seen in step 5 and that forms the double bond. I wanted to have H2O as a product also and this made sense. Thanks for you help.

Also, what program did you to draw the structures?

Title: Re: single ring to double ring synthesis
Post by: Rico on November 18, 2007, 11:33:01 AM

Since the secondary carbocation really isn't that stable i would suggest that the mechanism occurs in a concerted fashion. The methyl group leaves, attacks the oxygen-carbon and kicks out the water leaving group giving the tertiary carbocation (see jpeg attached). All happening in one step.

Title: Re: single ring to double ring synthesis
Post by: phillyj on November 18, 2007, 04:33:57 PM

thanks for the help. that seems reasonable.

how do you guys draw the reactions what program do you use?