An environmentally benign access to carbamates and ureas Isabelle Vauthey, FreÂdeÂric Valot, Christel Gozzi, Fabienne Fache and Marc Lemaire* Laboratoire de Catalyse et Synthe Áse Organique, Unite  Mixte de Recherches 5622, Universite  Claude Bernard Lyon I, Ba Ãt. 308 CPE, 43 Bd du 11 novembre 1918, 69622 Villeurbanne Cedex, France Received 14 March 2000; accepted 20 June 2000 Abstract Ureas were synthesized from methyl carbamates which were obtained by reaction of amines with dimethylcarbonate. Both reactions were catalyzed by g-Al 2 O 3 . # 2000 Elsevier Science Ltd. All rights reserved. Keywords: carbamate synthesis; urea synthesis; heterogeneous catalysis; dimethylcarbonate. The carbamate and urea functions are widely encountered in the structure of biologically active compounds. These compounds are generally prepared from phosgene, 1,2 phosgene derivatives 3,4 or isocyanates 5 in reaction with alcohols in the case of carbamates and amines in the case of ureas. Nevertheless, none of these methods are environmentally benign (use of toxic reagents and generation of by-products). In the case of carbamates, numerous methods have been described to avoid such drawbacks. Tetraethylammonium hydrogen carbonate (Et 4 NHCO 3 ) 6 was recently described as a safe reagent to obtain carbamates from amines but this method generates salts as by products. Hofmann rear- rangement 7,8 also allowed the synthesis of carbamates from amides. Mono- and di-substituted ureas were obtained by reductive alkylation of aromatic ureas using an aldehyde with NaBH 4 and TMSCl. Nevertheless, this is only suitable for aromatic aldehydes. 9 Solid-phase synthesis is used more and more for the obtention of urea libraries using thiophenoxy carbonyl linker 10 or 1,1 0 - carbonylbisbenzotriazole. 11 Heterogeneous catalysis has also been reported for carbamate and urea synthesis. For example, platinum group metals have been developed to catalyze the alkoxycarbonylation of amines leading to carbamates. 12,13 Nevertheless, this reaction requires the use of carbon monoxide. Zinc, as well, promoted the synthesis of carbamates starting from chloroformates and amines. 14 Dimethylcarbonate was used with lead derivatives as catalysts for the synthesis of methyl-N-phenylcarbamate from aniline. 15 Tin derivatives were also patented for 0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(00)01051-0 Tetrahedron Letters 41 (2000) 6347±6350 *Corresponding author. Fax: 33 (0) 4 72 43 14 08; e-mail: marc.lemaire@univ-lyon1.fr