Vibrating_Lights (Hive Addict)
07-25-02 03:25
No 336752
      Making the 3,4MD benzyl ketone  Bookmark   

Swim has become interested in researching M-Alpha.  What is the general procedure for getting the =O  on to the alpha carbon.  Swim has found a commercial source for The pipronyl alcohol that could be oxidised to the benzyl ketone but would rather do it him self.  Would a peracetic on safrole do the trick????
 
 
 
 
    Rhodium
(Chief Bee)
07-26-02 09:01
No 337293
      3,4-Methylenedioxypropiophenone is what you ...
(Rated as: excellent)
 Bookmark   

3,4-Methylenedioxypropiophenone is what you are looking for.

If you necessarily want to make it from isosafrole, see Patent GB898581 but use aqueous KOH instead of alcoholic KOH in the hydrolysis of the dihalo intermediate, that should yield the propiophenone, but it is a lot of guesswork.

Another way is to make the piperonylonitrile from piperonal (with hydroxylamine and an anhydride), then react that with ethylmagnesium bromide in a grignard reaction to form 3,4-methylenedioxypropiophenone. This process is detailed in J. Org, Chem. 13, 489-493 (1948).

The Grignard reagent acted on 9.85 g. of the nitrile in the usual manner to give 2.3 g. of practically pure starting material in the neutral fraction and 9.4 g. of solid yellow imine. The crude imine melted at 36-38C and gave a white hydrochloride; m.p. 143-144C. It proved too easily hydrolyzed to be analyzed, and 3 g. of the imine was accordingly converted to the ketone by treatment with warm acid. This compound weighed 2.5 g. and melted at 38-39C, the reported melting point of 3,4-methylenedioxypropiophenone. The phenylhydrazone, reported to melt at 97C, was prepared but melted at 106-107C. However, the melting points of the semi-carbazone, m.p. 185-187C, and the oxime, m.p. 103-104C, agreed well with the reported values of 187-188C and 104C, respectively.


General procedure for reaction of ethylmagnesium bromide with the benzonitriles.

2,6-Dimethoxybenzonitrile.

The nitrile (12 g.) suspended in a mixture of 50 ml. of ether and 50 ml. of benzene was added
in four approximately equal portions at fifteen-minute intervals to a Grignard reagent prepared from 3.5 g. of magnesium, 16 g . of ethyl bromide, and 100 ml. of ether. After the addition was completed the mixture was stirred for four hours at room temperature and
overnight under reflux. The products were isolated by usual procedures. A small amount
(0.8 g.) of unchanged 2,6-dimethoxybenzonitrile was recovered along with 11 g. of the crude
imine of 2,6-dimethoxypropiophenone (m.p. 68-72C).