Oxamide formation, double carbonylation

The alkylurea 576 and oxamide 577 are formed by oxidative carbonylation of amines under CO pressure using Pd/C as a catalyst[518]. The urea formation proceeds under atmospheric pressure using PdCh and CuCl2[519]. The mono-and double carbonylations of / -aminoethanol (578 and 579) afford the cyclic carbamate (oxazolidinones) 580 and oxamide (morpholinediones) 581 [520,521]. 

Under appropriate conditions, alcohols and amines can undergo an oxidative double carbonylation process, with formation of oxalate esters (Eq. 34), oxamate esters (Eq. 35) or oxamides (Eq. 36). These reactions are usually catalyzed by Pd(II) species and take place trough the intermediate formation of bis(alkoxycarbonyl)palladium, (alkoxycarbonyl)(carbamoyl)palladium or bis(carbamoyl)palladium complexes, as shown in Scheme 29 (NuH, Nu H = alcohol or amine) [227,231,267,293-300]. 

F. OXAMIDE, OXALATE, AND OXAMATE FORMATION FROM PALLADIUM-CATALYZED DOUBLE CARBONYLATION... 

Oxamides, dialkyl oxalate esters, and oxamic add esters can be prepared by Pd-catalyzed double carbonylation of secondary amines and alcohols via incorporation of two molecules of carbon monoxide into amines and/or alcohols. Pd-catalyzed double carbonylation reactions of amines in the absence or presence of alcohol were reported earlier to give ox-amides and oxamic acid ester.t i t Selective formation of oxamides has been achieved by double carbonylation of secondary amines in the presence of iodide ion and dioxygen catalyzed by Pd(OAc>2 (Eq. 

The mechanism for the formation of oxamides was proposed as shown in Scheme Pd-catalyzed cross double carbonylation of secondary amines and alcohols to give oxamic acid esters together with the formation of earbamate, mea, and oxamide was also developed by employing Cul as a eoeatalyst. In a stoichiometric reaction, oxamate can be formed selectively by treatment of PdCl2(MeCN)2 with a secondary amine and alcohol under CO (Eq. 22). ... 

In all these syntheses of ureas, a side reaction of either double carbonylation to oxamides takes place, or the formation of isocyanates probably by amine-elimination reaction from urea. It was been, therefore, important to find a synthesis with high selectivity, to minimize the side reactions. 

---