4- purin-9-imine, formation

Cyclopropylamines react with aldehydes to yield the corresponding imines in fair yield.Cyclopropane-1,2-diamine reacted with two equivalents of benzaldehyde to give corresponding diimine 1 in 58% yield. Imine formation is also involved as the key step in multistep reactions leading to a variety of complex compounds. For example, 4-[2,2-bis(benzyloxymethyl)cyclopropylamino]-6-chloro-5-formamidopyrimidine (2) reacted with triethyl orthoformate in the presence of hydrochloric acid to give purine derivative 3 in 58% yield. An analogous reaction took place when 1-azido-l-vinylcyclopropane was treated successively with triphenylphosphane and benzaldehyde to give iV-benzylidene-l-vinyl-cyclopropylamine in almost quantitative yield. 

Purine Synthesis. Aminopyrimidines and aminouracil derivatives can be converted into purines with diethyl azodicarboxylate in a number of closely related synthetic methods. Treatment of compound (1) with an aldehyde leads to the formation of imine (2), which is converted to purine (3) with DAD (eq 4). A number of researchers have applied variations of this approach. Treatment of 6-aminouracils or 6-aminopyrimidines (unsubstituted at the 5-position) with DAD leads to the initial formation of hydrazino Michael adducts. Treatment of these adducts with excess DAD leads to cyclization (eq 5). 

---