The preparation of 2‐penten‐1‐yl and 3‐methyl‐2‐buten‐1‐yl derivatives of adenine 2a,b, 7‐deazaadenine 2c,d, 2‐aminopurine 4a,b and 5a,b, 4‐aminopyrazolo[3,4‐d]pyrimidine 7a,b and 7‐amino‐v‐triazolo‐[4,5‐d]pyrimidine 8a–10a and 8b‐10b is described. The synthesis of compounds 2a‐d was accomplished by the functional group transformation reaction, whereas the synthesis of 4a‐8a and 4b‐8b was performed by the alkylation of the sodium salt of the heterocycles with alkenyl bromides. These alkenyl derivatives prepared as congeners of pentoxifylline (methylxanthine) were evaluated for their anti‐tumor necrosis factor a activity in human monocytic leukemia cells. Only compounds 7a and 7b exhibited significant activity and a poor toxicity profile in this assay. In peripheral blood mononuclear cells, compounds 7a and 7b, inhibited tumor necrosis factor a production in a dose dependent manner.