Manganese(I)-Catalyzed C-H Activation: The Key Role of a 7-Membered Manganacycle in H-Transfer and Reductive Elimination.

Nasiru P Yahaya,Jason M Lynam,Joshua T W Bray,Jessica Milani,Natalie E Pridmore,Conrad Wagner,Simon B Duckett,Adrian C Whitwood,L Anders Hammarback,Jonathan S Ward,Ian J S Fairlamb,Kate M Appleby,Magdalene Teh,Erik Troschke

doi:10.1002/anie.201606236

Nasiru P Yahaya, Jason M Lynam + Show 12 more

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https://doi.org/10.1002/anie.201606236

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Abstract

Manganese‐catalyzed C−H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered MnI intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at MnI by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C−H bond activation, serving as a valuable system for probing the mechanistic features of Mn C−H bond activation chemistry.

Highlights

CÀH bond activation–functionalization chemistry is a central arena for catalyst development and synthetic application.[1]
Our findings demonstrate that 4 g acts as a central manifold to reductive elimination and H-transfer, giving products 5 g and 6 g, respectively, with details described
Complex 2 g was fully characterized; a single crystal X-ray structure confirmed that regioselective CÀH activation occurred at C3, in keeping with PdII-direct arylations of 2-pyrones,[9] albeit most likely by a s-CAM-type process.[10]

Summary

Introduction

CÀH bond activation–functionalization chemistry is a central arena for catalyst development and synthetic application.[1] Transition metals mediate the efficient and selective activation of CÀH bonds, with recent attention focusing on environmentally benign and sustainable metals, for example, Mn, Co, Fe, and Cu.[2] MnI promotes CÀH activation of substrates containing nitrogen-directing groups.[3] For example, 1 gives cyclomanganated complex 2, with subsequent reaction with alkyne 3 forming a proposed 7-membered ring intermediate 4 (Scheme 1).[4] Formation of either 5, 6, or 7 results from reductive elimination, H-transfer, or dehydrogenative annulation, respectively. The green bonds show the newly formed bonds in the organic products, with red showing the insertion location of 3 (5 g not observed under these reaction conditions).

Results

Conclusion