Cyclization carbodiimide mediated

A general and efficient solid-phase synthesis of A-9-substituted 2,8-diamino purines 62 has been described. The key synthetic transformation uses a carbodiimide-mediated cyclization of a thiourea 60. The reaction was performed using microwave reaction conditions on solid phase <06TL8897>. 

The solid phase synthesis of many organic molecules utilizes carbodiimide mediated reactions. An example is the synthesis of l,4-benzodiazepine-2,5-dione using EDCCl in NMP in a key synthesis step. Often carbodiimides are used in the synthesis of complex proteins. A recent example is the synthesis of the tripeptide backbone of the novel immunosuppressent sanglifehrin A. In the synthesis of the marine alkaloid, variolin B, the formation of an annelated pyrimidine ring is achieved using a carbodiimide mediated cyclization process. 

Unexpected synthesis of rearranged 3,4-dihydroquinazolines by a sequential Ugi 4CC/aza-Wittig/ carbodiimide-mediated cyclization. 

Usually, carbodiimides obtained by an aza-Wittig reaction of A-vinyUc phosphazenes with isocyanates cannot be isolated. Therefore, the very reactive carbodiimides can be used as synthetic intermediates of polyheterocyclic natural products by domino processes involving aza-Wittig/intramolecuIar cycUzation (AW-IC). In the synthesis of variolin B (58), the formation of the annulated 2-aminopyrimidine ring 57 is achieved from phosphazene 56 by a tandem aza-Wittig/carbodiimide-mediated intramolecular cyclization process (Scheme 15.12). 

S-Hydroxy-l-azetidinones. A biomimetic synthesis of the y3-lactam 4 from BOC-L-serine (1) has been reported. The protected serine derivative is converted into the hydroxamic acid 2 by condensation with O-benzylhydroxylamine mediated by the water-soluble l-ethyl-3(3 -dimethylaminopropyl)carbodiimide (1, 371). The product is cyclized directly in high yield to the / -lactam 3 by treatment with diethyl azodicarboxylate and triphenylphosphine. No racemization is observed. Deprotection by catalytic hydrogenation gives the N-hydroxy-jS-lactam 4. Previous biomimetic syntheses of 2-azetidinones have involved cyclization ot /3-cMoroamides with sodium hydride (e.g., 7, 335). 

Scheme 1.8 Reaction chemistry of zirconacyclopentene and zirconocene-mediated cyclization of alkyne with aldehyde, ketone, nitrile, isocyanate,

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