[everydaygame]

Hi im a little confused about a mechanism from this three step synthesis of 7-methoxyphthalide:

http://i28.photobucket.com/albums/c209/every_day_game/CV9P0559.gif

I think im correct saying the first step is chlorination via the thionyl chloride followed up by an SN2 substitution by the DMF and that the final step is reduction of the aldehyde by the sodium borohydride leading to cyclisation as the charged Oxygen then attacks the other carbonyl group with the amine group leaving after gaining a proton and becoming charged when the oxygen delococalised pair kicks back in.

Correct me if thats wrong. What i dont see though how the second step works. Presumably the BuLi deportonates but where is the aldehyde group coming from?

If someone could point me in the right direction that would be amazing

Matt

[sjb]

Your 1st and 3rd steps seem reasonable to me.

As to the second, the carbonyl directs lithiation to the observed regioisomer.

Then the negative charge attacks the carbonyl of DMF, forming a tetrahedral intermediate, and the least worst leaving group to be kicked out on reformation of the carbonyl is the dimethylamide ion.

At least, that's my understanding.

A

[everydaygame]

Ive worked what you suggested through, I think what was confusing me was the regio chemistry not adding up in my head.

nice one