SYNTHESIS OF SYMMETRICALLY AND UNSYMMETRICALLY SUBSTITUTED ALPHA-DIONES FROM ORGANOMETALLIC REAGENTS AND 1,4-DIALKYLPIPERAZINE-2,3-DIONES

The reaction of an equimolar mixture of N,N'-dialkylethylenediamines and diethyl oxalate in diethyl ether or 2-propanol leads to 1,4-dialkylpiperazine-2,3-diones. As cyclic and nearly planar tetraalkyl oxamides, these compounds are able to react with 2 equiv of organolithium or Grignard compounds to form, after hydrolysis, symmetrically substituted alpha-diones in excellent yields. The sequential addition of 1 equiv each of two different organolithium compounds affords unsymmetrically substitute alpha-diones when the more soluble longer chain dialkyl derivatives of piperazine-2,3-dione are employed. The dialkylethylenediamines can conveniently be recovered and recycled to the 1,4-dialkylpiperazine-2,3-diones in good yields.