The behaviour of 6‐ and 8‐substituted purines toward potassium amide in liquid ammonia. A new example of tele‐amination

Reaction of 6‐chloro‐ and 6‐(methylthio)purine with potassium amide in liquid ammonia leads to the formation of adenine. When these aminations are carried out with 15N‐labelled potassium amide, the 15N label is found to be present in the amino group, proving that these reactions do not involve opening of the pyrimidine ring. Low temperature 1H‐ and 13C‐NMR spectroscopy of solutions of 6‐chloro‐ and 6‐(methylthio)purine in liquid ammonia, containing potassium amide give no evidence for the presence of an intermediary σ‐adduct. 8‐Chloro‐ and 8‐(methylthio)purine undergo a Tschitschibabin amination at position 6 leading to 8‐chloro‐ and 8‐(methylthio)adenine. In addition 8‐chloropurine gives adenine. Evidence is presented that the formation of this product proceeds via a tele‐amination. 6‐tert‐Butyl‐8‐(methylthio)purine and 8‐aminopurine are found to be unreactive towards potassium amide.