Palladium Catalyzed Synthesis of Münchnones from α‐Amidoethers: A Mild Route to Pyrroles

Abstract

Eine milde Palladiumkatalyse aktiviert die Kohlenstoff‐Sauerstoff‐Bindung von α‐Amidoethern in Carbonylierungen (siehe Schema). Ein in situ erzeugtes Münchnon geht eine 1,3‐dipolare Cycloaddition mit Alkinen ein, die zu substituierten Pyrrolen als Produkten führt.

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…The latter approaches have been suggested to proceed via cycloaddition reactions between mesoionic intermediates with the alkyne components [727,728]. Intermediate m€ unchnones can also be generated by a palladium-catalyzed reaction between certain a-amidoethers with carbon monoxide, eventually affording pyrroles via cycloadditions with suitable alkynes [729]. Additional efforts resulted in conversion of 1,3-dicarbonyl compounds, arylglyoxals, and ammonium acetate into 2-alkyl-5-aryl-4-hydroxypyrroles in water as the reaction medium [730], and preparation of 4,5-dimethylpyrrole-2,3-dicarboxylates by cyclizations of butane-2,3-dione with ylides derived from acetylenedicarboxylates and ammonium acetate in the presence of triphenylphosphine [731].…”

Catalyst‐Dependent Divergent Synthesis of Pyrroles from 3‐Alkynyl Imine Derivatives: A Noncarbonylative and Carbonylative Approach

“…[20] The substrate generality of the carbonylative pyrrole synthesis was also examined. The reactions proceeded smoothly when the R 2 substituent was changed from a simple alkyl group to a benzyl, PMB, or 2-phenylethyl group to afford the desired products in moderate to good yields (Table 3, entries [1][2][3][4][5]. The substituent on the alkyne functionality could also tolerate a substituted phenyl group or thienyl, which provided the desired products in yields ranging from moderate to good (Table 3, entries [6][7][8][9][10][11].…”

“…[1,4] In addition to the traditional methods, such as the Knorr pyrrole synthesis, transition-metal-catalyzed approaches have also been developed. [5] However, new and practically useful synthetic methods are still highly desirable.…”

A Palladium‐Catalyzed Multicomponent Coupling Approach to π‐Conjugated Oligomers: Assembling Imidazole‐Based Materials from Imines and Acyl Chlorides

“…This can in principle be favored by forming a more-electron-rich palladium catalyst. Replacing dba with a stronger donor, PPh 3 , inhibits the reaction (entry 2), presumably because of its strong coordination to palladium blocking subsequent carbonylation (step c); [15] however, bulky, electron-rich phosphines can increase yields to 48 % (entry 3). A second byproduct in this reaction is the a-sulfonyl-substituted amide 7, [18] which results from the reaction of TolSO 2 À with the in situ generated 6.…”

“…Palladium catalysis can provide a potential mechanism to selectively couple these units together by mediating the series of steps outlined in Scheme 2. This approach is based on our recent efforts in metal-catalyzed multicomponent reactions, [15] including imidazole synthesis, [16] and involves the catalytic synthesis of mesoionic 1,3-oxazolium-5-oxides, commonly referred to as Münchnones (2), from imines, acyl chlorides, and CO (steps a-e).…”