Author Topic: High yield aldoxime --> nitrile conversion  (Read 1280 times)

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High yield aldoxime --> nitrile conversion
« on: November 20, 2002, 03:54:00 PM »
SWIM found brief mention of obtaining nitriles from aldoximes through TFSE, but nothing regarding this method. While doing some research on the Beckmann Rearrangement, SWIM came across an article where 2,4,6-trichloro[1,3,5]triazine (TCT) in N,N-DMF is used to perform the rearrangement in high yields at room temp. TCT is also known as cyanuric chloride, and is extremely cheap. The TCT forms a complex with the DMF, which is what actually performs the rearrangement. There is a blurb about aldoximes to nitriles however...

This from JOC, 2002, 67, 6272-6274 entitled "Beckmann Rearrangement of Oximes under Very Mild Conditions."

General Procedure.  The procedure for the preparation of 7-ethylazepan-2-one (run 12) is representative.  TCT (1.83g, 10.0 mmol) was added to DMF (2 mL), maintained at 25C.  After the formation of a white solid, the reaction was monitored (TLC) until the complete disappearance of TCT.  Then 2-ethylcyclohexanone oxime (1.41g, 10.0 mmol) in DMF (15 mL) was added.  After the addition, the mixture was stirred at roomt emperature, monitored (TLC) until completion (8 h).  Water (20 mL) was added then the organic phase washed with 15 mL of a saturated solution of Na2CO3, followed by 1N HCl and brine.  The organic layer was dried (Na2SO4), and the solvent evaporated to yield 7-ethylazepan-2-one that was isolated without further purifications (1.41g, 100%)

   Aldoximes seem apparently to show a different reaction trend.  Under the same conditions, treatment of aldoximes with the TCT/DMF complex in DMF affords rapidly and quantitatively the corresponding nitrile (Scheme 2).  The reactions are rapid and quantitative, the nitrile being the only product recovered from the reaction mixtures.
    Although conversion of aldoximes to nitriles through dehydration using TCT is already documented[13], this reaction should not proceed through dehydration sequences as no added base is present in the reaction medium that is acidic.
...... The subsequent rearrangement to adduct 3 should then afford directly the nitrile, in the case of aldoximes ... upon hydrolitic workup.

Scheme 2
  RCHO  -->  RCHNOH  --[TCT/DMF, DMF, r.t. 4h]--> RCN, 100%

[13] Chakrabarti, J. K.; Hotten, T. K. J. Chem. Soc., Chem. Commun. 1972, 1226.

A possibility occured to SWIM along the lines of, condensation of 2,5-DMBA (for example...) with nitromethane, reduction of the nitroalkene to the aldoxime with SnCl2, conversion to the nitrile, then reduction by any number of means to 2CH.

Of course, if the NaBH4/Ni2B reduction effectively reduces nitroalkenes to amines, then this wouldn't be of much importance, but anyway, hope you guys liked it.