Microwave‐Assisted Aminocarbonylation of Ynamides by Using Catalytic [Fe₃(CO)₁₂] at Low Pressures of Carbon Monoxide

Abstract

The microwave-assisted aminocarbonylation of ynamides at low pressures of CO is reported. A new class of (E)-acrylamides that are potentially suitable for several applications has been regioselectively synthesized after microwave irradiation for only 20 min by using eco-friendly [Fe(3)(CO)(12)] as the catalyst precursor and triethylamine as the ligand. This transformation is atom economic as all reactants are used in stoichiometric quantities. Furthermore, the transformation is efficiently applied to the alkoxycarbonylation of alkynes as well. Moreover, running these reactions under microwave irradiation allows the simplification of the reaction conditions with remarkable reductions in time, temperature and gas pressure.

Gaseous Reactants in Microwave‐Assisted Synthesis

“…Mainly primary amines were reacted, whereas addition of CO took place regioselectively at the terminal alkyne moiety, resulting in α, β-unsaturated amides. Similarly to hydroxycarbonylation with Mo(CO) 6 [29], the present method forms the respective methyl cinnamates on reaction with MeOH as the nucleophile [33]. Racemization of the asymmetric carbon atom in (S)-1-phenylethanamine was not observed during the reaction.…”

“…The examples discussed so far involved reactions of sp 2 carbon-halogen bonds [28,32], but carbon-carbon triple bonds can also be used as centers for reactivity. Thus, aminocarbonylation of ynamides with 0.13 MPa CO at 90 • C afforded the respective acrylamides (Scheme 11.8) in acceptable yields (44-90%) [33]. Reactions were catalyzed using [Fe 3 (CO) 12 ] and NEt 3 as the base.…”

“…Hydroxycarbonylation reactions, which have been mentioned in connection with the aminocarbonylation studies of Kaiser et al [29] and Pizzetti et al [33], were intensively investigated by Kormos and Leadbeater (Scheme 11.9) [34]. Performing the reaction in water as nucleophile and solvent in the presence of Na 2 CO 3 allowed the formation of benzoic acids from several aryl iodides if pressurized with 1.4 MPa CO. Investigation of the reaction conditions revealed that even catalyst concentrations of 0.001 mol% Pd resulted in the formation of the desired product.…”

“…Isolated yields ranged from 70 to 97%, whereas sterically hindered triflates (2,6-or 2,5-substitution) or those with MeO groups afforded the carboxylic acids in lower yields (15-56%). Similarly to methoxycarbonylation with Mo(CO) 6 in MeOH [33], several alcohols were applied as nucleophiles, unifying the roles of reactant and solvent for the Pd(OAc) 2 -catalyzed procedure with gaseous CO (Scheme 11.9) [36]. In comparison with the proposed method for the formation of aromatic carboxylic acids [34], the reaction needed a lower partial pressure of CO (1 MPa) and the reaction temperature could be reduced to 125 • C instead of 165 • C [36].…”

Domino Reactions Triggered by Hydroformylation

“…Microwave cavities are usually equipped with vessels able to resist high temperature, and pressures of maximum 20 atm, which leads to small autoclaves where the energy source for heating is microwave irradiation. Different protocols for the introduction of gas reagents inside a microwave cavity have recently been developed by different groups, demonstrating that hydrogenations [70,71], carbonylations [72][73][74], and HF [75] can be easily run inside a microwave working in milder reaction conditions with respect to traditional heating, especially in terms of gas pressures and reaction temperatures [76]. Since the first report on microwave-assisted HF reaction [75], several application of this protocols to domino transformations have been reported, leading to efficient access to chemically and biologically interesting heterocycles and amines.…”