General information S2Characterization data for amine substrates 1 S2Carboxylative cyclization of 1-methylamino-2-butyne with mixed gases S4Characterization data for 2 S4 Synthesis of 3a S7 X-ray structure determination for 2a and 3a S8References S10NMR spectra of 1-3

The carboxylative cyclization of a range of propargylic amines using carbon dioxide (CO 2 ) is promoted by IPr-gold(I) (IPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene) complexes to afford (Z)-5-alkylidene-2-oxazolidones in methanol under mild conditions, even in the absence of additives such as silver salts and bases. Investigation of the substrate scope shows that the catalytic performance is markedly retarded by the introduction of aromatic substituents at the alkyne terminus. The formation of alkenylgold(I) complexes as catalytic intermediate models is demonstrated by the treatment of methyl-and phenyl-substituted propargylamines with AuOH(IPr) under a CO 2 atmosphere. A comparison of the reactivity of the alkenylgold(I) complexes clearly indicates that the alkenyl ligand attached to an alkyl group at the  position is more susceptible to protonolysis compared with that attached to a phenyl group. These results and kinetic experiments corroborate a catalytic cycle that involves the nucleophilic attack of carbamate at the C-C triple bond bound to the Au center and its subsequent protodeauration to release the cyclic urethane products.

Silver(I) carboxylate complexes promote the carboxylative cyclization of allenylmethylamines to afford 5-alkenyl-1,3-oxazolidin-2-ones in 2-propanol. The use of an N-heterocyclic carbene ligand (IPr) under pressurized CO2 is effective in suppressing the intramolecular hydroamination that leads to 2,5-dihydropyrroles. The mechanism involving a nucleophilic attack of the carbamate of the allene moiety and a subsequent protonation was realized on the basis of experimental and theoretical results involving a model intermediate, the alkenylgold(I) complex, which was synthesized from Au(OH)(IPr) and 1-methylamino-2,3-butadiene.

Abstractleading to 5‐alkenyl‐1.3‐oxazolidin‐2‐ones