Primary amine- urea-mediated

The last example focuses not on the functionalization of heterocycles by a transition metal mediated carbon-heteroatom bond forming reaction, but the palladium catalyzed conversion of primary amines, including amino-heterocycles, into urea derivatives. A representative example, shown in 8.38., includes the reaction of an amino-carbazole derivative with morpholine, carbon monoxide and oxygen in the presence of catalytic amounts of palladium(II) iodide. The formation of the urea moiety proceeds with great selectivity and in high yield.49 The reaction works equally well for primary aliphatic and aromatic amines. 

C-labeled carbamoyl compounds can be prepared by using a selenium-mediated reaction with [ carbon monoxide. The urea formation works excellent in the case of cyclizations but in other cases satisfactorily only with primary amines (Kihlberg et al. 2002). Since selenium is practically insoluble in most solvents the use of primary alkyl amines or tetrabutylammonium fluoride is necessary for the formation of soluble and reactive complexes with selenium. Except for ring closures, rhodium-promoted carbonylations are probably more useful than the corresponding selenium reactions (Ohad et al. 2009). 

In 2005, Larhed s group presented extremely fast cobalt carbonyl mediated syntheses of ureas from primary amines [39]. A protocol was developed where a primary amine, Co2(CO)8 (0.66 equiv.) and triethylamine (2 equiv.) in acetonitrile... 

Ureas prepared from primary allylic amines slowly decomposed under the conditions listed without providing any cyclized products. Furthermore, the synthesis of amino sugars by the IBX-mediated cyclization protocol was also accomplished. This method was found to be stereoselective. A few examples are listed below ... 

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