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16.17.1.2.3 Method 3: Cyclization with Aldehydes

DOI: 10.1055/sos-SD-016-01192

Seela, F.; Ramzaeva, N.; Rosemeyer, H.Science of Synthesis, (200416974.

Condensation of a 5,6-diaminouracil with an aldehyde followed by ring closure of the 5-(alkylideneamino)-6-aminouracil intermediate (Schiff base) is the most commonly used route for the synthesis of 8-substituted xanthines. These preparations are frequently performed in one pot[‌174‌,‌212‌] (without addition of an oxidant), although in many cases the reaction conditions for the ring closure can be forcing. Commonly employed procedures for this step use an aqueous inorganic base at reflux temperature or oxidative cyclization [e.g., I2, DME, 50°C;[‌213‌] DEAD, DMF, 100°C;[‌214‌] DEAD, glyme, reflux;[‌215‌] DEAD (neat), heat;[‌216‌] SOCl2, reflux;[‌174‌,‌217‌] HgCl2, DMSO, rt;[‌218‌] FeCl3, EtOH, reflux;[‌174‌,‌185‌,‌219‌] FeCl3, AcOH;[‌220‌] NBS, CHCl3, reflux;[‌221‌] or MCPBA, MeCN, rt[‌222‌]]. An example is shown for the formation of xanthine 38 via ring closure of 6-amino-5-(ethylideneamino)uracil using 3-chloroperoxybenzoic acid in acetonitrile at room temperature (Scheme 30).[‌222‌]

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