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The effects of β‐hydrogen‐containing alkyl Grignard reagents in simple ferric salt cross‐couplings have been elucidated. The reaction of FeCl3 with EtMgBr in THF leads to the formation of the cluster species [Fe8Et12]2−, a rare example of a structurally characterized metal complex with bridging ethyl ligands. Analogous reactions in the presence of NMP, a key additive for effective cross‐coupling with simple ferric salts and β‐hydrogen‐containing alkyl nucleophiles, result in the formation of [FeEt3]−. Reactivity studies demonstrate the effectiveness of [FeEt3]− in rapidly and selectively forming the cross‐coupled product upon reaction with electrophiles. The identification of iron‐ate species with EtMgBr analogous to those previously observed with MeMgBr is a critical insight, indicating that analogous iron species can be operative in catalysis for these two classes of alkyl nucleophiles. The reactivity of β‐hydrogen‐containing alkyl Grignard reagents in simple ferric salt cross‐couplings was studied. Whereas [Fe8Et12]2− is formed upon reaction of simple ferric salts and EtMgBr in THF, the addition of N‐methylpyrrolidone (NMP) leads to the formation of [FeEt3]−. Overall, these studies demonstrate that similar iron species are accessible for alkyl Grignard reagents containing or lacking β‐hydrogen atoms. [ABSTRACT FROM AUTHOR]

Abstract: The use of N‐methylpyrrolidone (NMP) as a co‐solvent in ferric salt catalyzed cross‐coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross‐coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP)6][FeMe3]2 (1), which forms as the major iron species in situ in reactions of Fe(acac)3 and MeMgBr under catalytically relevant conditions where NMP is employed as a co‐solvent. Importantly, combined GC analysis and 57Fe Mössbauer spectroscopic studies identified 1 as a highly reactive iron species for the selective formation generating cross‐coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of 1 over [Fe8Me12]− cluster generation, which occurs in the absence of NMP. [ABSTRACT FROM AUTHOR]

The discovery and elucidation of a new Nazarov cyclization/Wagner-Meerwein rearrangement/oxidation sequence is described that constitutes an efficient strategy for the synthesis of 4-alkylidene cyclopentenones. DFT computations and EPR experiments were conducted to gain further mechanistic insight into the reaction pathways. [ABSTRACT FROM AUTHOR]