[aznbeayst]

hey guys i dunno if you guys will be able to help me but these questions are sooo hard and i have no clue where to start.... can someone help me out or throw a couple of hints... im so lost

i have to do 2 but help with ANY will put me a step closer to accomplishing this problem. i would appreciate it soo much.. advanced organic chem was the worse decision ever, lol.. this is all a blur to me!!!!

[Albert]

This could be a way of solving reaction 2.


For what concerns the former reaction, are you sure that to be the molecule you have start from?

[aznbeayst]

here is the problem.. thanks albert for helping me... and yes that is the beggining product... sigh..

[green-goblin]

Is the starting structure of number two definitely drawn out right? If it the epoxide group was acting as a bridging species between the two rings it would just be the ring opening of an epoxide?

[aznbeayst]

hey, yes that is definitely the structure (i scanned the page) .. if it were an epoxide opening though, how would i be able to get the other OH group on the other side?

[Albert]

Take a look at this: I took inspiration from the synthesis of methacycline.

[aznbeayst]

thanks albert.. i dont quite understand the 2nd (H, H2O) and third step (hv). can you explain to me what exactly is going on? omg i suck at chem

[Albert]

The steps you want me to explain are those I consider the most probable of all the pathway.

The former is the opening of oxacyclopropane in acid. I think the product I drew is the most common because of steric hindrance.

The latter is taken from the synthesis of methacycline and hv (which is the Greek letter vi) means that it is a radical reaction. The precise mechanism is unknown to me: let's see whether or not there's someone who knows it.  

[alphahydroxy]

I guess this is the route for question 3....



Albert, forgive me if this is stupid question but it is getting late..

why would opening of the epoxide give the gem-diol rather than the 1,2-diol? surely if you spring the epoxide with a nucleophile it must give the 1,2 product..?

[movies]

Albert: check out the mechanism for formation of tetrahydrofuran rings from alkanols using a radical oxidant like Pb(OAc)₄.  I know that it is listed under Pb(OAc)₄ in the Encyclopedia of Reagents for Organic Synthesis.  The mechanism with NCS will be pretty similar.

Alphahydroxy: in the last step of your mechanism you ought to have an S_N1 mechanism rather than an S_N2 mechanism.  S_N2 reaction at a fully suybstituted carbon is exceedingly slow.

For #1, what do you suppose would be the first step of the mechanism?  Start pushing electrons!

[aznbeayst]

thanks so much you guys.. i really appreciate you taking the time to help me out... is there something im missing because some of the rxns i've never seen in my life.. is there a website you guys are getting all your sources from or is this general knowledge you all know already that i dont?  

[movies]

Lots of practice.  I'm sure each of us has been in your position at one time or another.

If you are looking for good resources, check the Good Chemistry Books thread.  There are lots of good name reaction websites out there as well.  If you become familiar with some those mechanisms, then you will soon be able to predict the mechanism for other reactions.

[aznbeayst]

thanks movies, ill have to look into the book


does anyone know #1 by any chance? tried doing a SN1 reaction with the CN- attacking the carbon and making the -BR chain leave, but that doesnt work and then i tried shifting electrons around and i still cant figure it out...

anyone? thanks

[movies]

This should get you started....