A phosphine-free catalytic system [Pd(OAc)
2-Cu(OAc)
2-air] induced a substrate-specific carbonylationof amines in boiling toluene under CO gas (1 atm). Symmetrical
N,
N'-dialkylureas were obtained by thecarbonylation of primary amines.
N,
N,
N'-Trialkylureas were selectively formed by addition of a secondaryamine to the above reaction vessel. Secondary amines did not give tetraalkylureas. However, dialkylamineswith a phenyl group on their alkyl chains, such as
N-monoalkylated benzylic amine or phenethylaminederivatives, underwent a direct aromatic carbonylation to afford five- or six-membered benzolactams. Inthe carbonylation, the chelation effect or steric repulsion between Pd(II) and the
meta-substituent in the
ortho-palladation and the ring sizes of cyclopalladation products that were formed prior to carbonylationwere found to generate good site selectivity and increase the reaction rate. In contrast, carbonylation of
![](/images/gifchars/omega.gif)
-arylalkylamines with a hydroxyl group gave neither ureas nor benzolactams but instead produced 1,3-oxazolidinones smoothly. Hydrochlorides of amines also underwent carbonylation to afford thecorresponding amides under the conditions used. This procedure made it possible to prepare ureas ofamino acid esters and
N-alkylcarbamates in practical yields.