A general method for the synthesis of dipeptides has been developed, which does not require any coupling reagents. This method is based on the reaction of readily available HCl salts of amino acid methyl esters with tetrabutylphosphonium amino acid ionic liquids. The isolation procedure of stepwise treatment with AcOH is easy to carry out. The method was extended to the synthesis of tripeptide, tyrosyl-glycyl-glycine, present in IMREG-1, also.

Bis(cyclopentadienyldicarbonyliron) ([CpFe(CO) 2 ] 2 ) serves as a carbon monoxide source in carbonylative coupling reactions. Treatment of aryl iodides with primary amines in the presence of DBU and [CpFe(CO) 2 ] 2 under palladium catalysis provides the corresponding benzamides in good yields. Similar reactions with phenols and thiols provide the corresponding benzoate esters and thioesters, respectively. A catalytic amount of DMAP as an additive promoted the carbonylative coupling reactions with primary alcohol and secondary amine.Transition-metal-catalyzed carbonylative cross-coupling reactions in the presence of carbon monoxide are useful methods for synthesizing carbonyl compounds. 13 Because of the inherent difficulty in handling highly toxic carbon monoxide, considerable efforts have been made to develop carbon monoxide equivalents to achieve CO-gas-free carbonylation. 4 Organic carbonyl compounds such as pentafluorobenzaldehyde and N,Ndimethylformamide are known to serve as carbon monoxide equivalents. 57 However, the scope of substrates and hence the diversity of products are limited. Alternatively, metal carbonyl complexes are also useful as carbon monoxide sources since they emit carbon monoxide upon heating. [Ni(CO) 4 ] was first used stoichiometrically in carbonylative reactions. could be reduced to 0.75 equiv without significantly deteriorating the yield (Entry 2). In the presence of 0.38 equiv of [CpFe(CO) 2 ] 2 (1.5 equiv of CO), the reaction proceeded cleanly to afford a 70% yield of 1a, the remainder of mass balance being unreacted 4-iodotoluene (Entry 3). To increase the efficiency of the reaction with 0.38 equiv of [CpFe(CO) 2 ] 2 , we further examined the effect of ligand. Tricyclohexylphosphane slightly improved the yield to 79% (Entry 5) whereas triphenylphosphane and bidentate 1,2-bis(diphenylphosphano)ethane had no and adverse effects, respectively (Entries 4 and 6). The choice of strong organic bases such as DBU and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN, Entry 7) is critical. Other organic bases such as 1,4-diazabicyclo[2.2.2]octane, tributylamine, and pyridine as well as inorganic bases such as cesium carbonate and potassium t-butoxide failed to promote the reaction. In analogy with the molybdenum-mediated carbonylation, 9b DBU would strongly coordinate to iron, which leads to irreversible release of carbon monoxide from iron carbonyl complexes.Finally, the use of 2 equiv of iodobenzene and a prolonged reaction time could improve the yield of 1b (based on 4-toluidine) while reducing the amount of the palladium catalyst to 1 mol % (Table 2, Entry 1).13

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Strike while the iron is hot! A BF3‐mediated formal [2+2] cycloaddition between (1‐alkynyl)iron complexes and aromatic aldehyde imines occurs, which is followed by ring‐opening of the initially formed azacyclobutenes to yield (2‐alkenyl‐1‐imino)iron complexes (see scheme). The resulting iron complexes undergo deferric substitution reactions with water under oxidative conditions to afford the corresponding cinnamamides with high E selectivity.