Manganese‐Catalyzed Dehydrogenative Alkylation or α‐Olefination of Alkyl‐Substituted N‐Heteroarenes with Alcohols

Abstract

Catalysis with earth-abundant transition metals is an option to help save our rare noble-metal resources and is especially interesting when novel reactivity or selectivity patterns are observed. We report here on a novel reaction, namely the dehydrogenative alkylation or α-olefination of alkyl-substituted N-heteroarenes with alcohols. Manganese complexes developed in our laboratory catalyze the reaction with high efficiency whereas iron and cobalt complexes stabilized by the same ligands are essentially inactive. Hydrogen is liberated during the reaction, and bromine and iodine functional groups as well as olefins are tolerated. A variety of alkyl-substituted N-heteroarenes can be functionalized, and benzylic and aliphatic alcohols undergo the reaction.

Phosphine Ligand‐Free Ruthenium Complexes as Efficient Catalysts for the Synthesis of Quinolines and Pyridines by Acceptorless Dehydrogenative Coupling Reactions

“…[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][60][61][62][63] Metal-ligand cooperative catalysis [64][65][66][67] can dramatically improve catalytic performance of ADC reactions using pincer ligands bearing NH, OH or CH 2 functionality. [40][41][42][43][44][68][69][70][71][72][73][74][75][76][77][78][79][80][81] Milstein, [40] Sun, [41] Yu, [42] Kundu [43] and Chen [44] have independently developed bifunctional Ru(II) catalysts for the synthesis of pyridine and quinoline derivatives (Scheme 1), but these catalysts were often air/water sensitive, involved a somewhat complicated synthesis, or required to...…”

Manganese Catalyzed Acceptorless Dehydrogenative Coupling Reactions

“…In 2018, the Maji et al and the Kempe's group independently reported manganese-catalyzed olefination of alkyl-substituted N-heteroarenes 12 with alcohols 1. While Kempe and coworkers approached the reaction with the PNPÀ Mn complex Mn-22 (Scheme 12a), [30] Maji et al used an in situ generated NNN-pincer stabilized complex Mn-23 for the ADC of Nheteroarenes 12 with 1 (Scheme 12b). [31] In both cases, it was found that the reaction was highly selective and gave only Zisomer of the olefination product 13.…”

Manganese‐Catalyzed C−H Olefination Reactions

“…Remarkably, water and hydrogen were eliminated as the byproducts, making this reaction fairly environmentally benign. At the same time, such an olefination reaction was also developed by Kempe's group, using a manganese catalyst supported by a PNP pincer ligand . A possible reaction mechanism was proposed after careful mechanistic studies (Scheme ).…”

“…At the same time, such an olefination reaction was also developed by Kempe's group, using a manganese catalyst supported by a PNP pincer ligand. [33] A possible reaction mechanism was proposed after careful mechanistic studies (Scheme 12). Initially, the real catalytic active manganese species Mn-8 was generated upon preactivation with a base.…”