Abstract
The Pd-catalyzed intramolecular carbene C–H insertion of α-diazo-α-(methoxycarbonyl)acetamides to prepare oxindoles as well as β-lactams was studied. In order to identify what factors influence the selectivity of the processes, we explored how the reactions are affected by the catalyst type, using two oxidation states of Pd and a variety of ligands. It was found that, in the synthesis of oxindoles, ((IMes)Pd(NQ))2 can be used as an alternative to Pd2(dba)3 to catalyze the carbene CArsp2–H insertion, although it was less versatile. On the other hand, it was demonstrated that the Csp3–H insertion leading to β-lactams can be effectively promoted by both Pd(0) and Pd(II) catalysts, the latter being most efficient. Insight into the reaction mechanisms involved in these transformations was provided by DFT calculations.
Highlights
In recent years, the development of new methodologies for the selective functionalization of unactivated C–H bonds has become a very active area of research [1,2]
In order to ascertain the thefactors factorsgoverning governing selectivity of processes, the processes, we explored how the reactions are thethe selectivity of the we explored how the reactions are affected ascertain the factors governing the selectivity of the processes, we explored how the reactions are affected by the substituents on α-diazoacetamide and the type of catalyst, using complexes with two by the substituents on α-diazoacetamide and the type of catalyst, using complexes with two oxidation affected by the substituents on α-diazoacetamide and the type of catalyst, using complexes with two oxidation
We have reported that the intramolecular carbene C–H insertion of α-diazo-α-(methoxycarbonyl)acetamides to form β-lactams can be effectively catalyzed by Pd(II)
Summary
The development of new methodologies for the selective functionalization of unactivated C–H bonds has become a very active area of research [1,2]. While the effectiveness of palladium complexes in catalyzing carbene C–H insertion reactions from α-diazo carbonyl compounds was demonstrated some time ago [28], their use has been restricted to a couple of examples of insertion into CAr sp2 –H bonds [29,30,31]. This fact is highly surprising if we take into account the great success of palladium catalysis in cross-coupling reactions of diazo compounds with organic halides, pseudohalides, or arylboronic acids [32,33,34,35] and Molecules 2019, 24, 3551; doi:10.3390/molecules24193551 www.mdpi.com/journal/molecules
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