Hoveyda-Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring. Synthesis of stable, industrially scalable, highly efficient ruthenium metathesis catalysts and 2-vinylbenzylamine ligands as their precursors.

Kirill B Polyanskii,Atash V Gurbanov,Fedor Ivanovich Zubkov,Eugeniya V Nikitina,Pavel V Raspertov,Pavel A Kumandin,Kseniia A Alekseeva

doi:10.3762/bjoc.15.73

Kirill B Polyanskii, Atash V Gurbanov + Show 5 more

Open Access

https://doi.org/10.3762/bjoc.15.73

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Abstract

A novel and efficient approach to the synthesis of 2-vinylbenzylamines is reported. This involves obtaining 2-vinylbenzylamine ligands from tetrahydroisoquinoline by alkylation and reduction followed by the Hofmann cleavage. The resultant 2-vinylbenzylamines allowed us to obtain new Hoveyda–Grubbs catalysts, which were thoroughly characterised by NMR, ESIMS, and X-ray crystallography. The utility of this chemistry is further demonstrated by the tests of the novel catalysts (up to 10−2 mol %) in different metathesis reactions such as cross metathesis (CM), ring-closing metathesis (RCM) and ring-opening cross metathesis (ROCM).

Highlights

Ruthenium-catalysed olefin metathesis reactions have been playing an important role in various fields of organic synthesis in the past three decades
The application of various catalysts is required to achieve the best results in each of the many directions of metathesis reactions such as cross metathesis – CM, ring-opening metathesis – ROM, ring-closing metathesis – RCM, ringopening metathesis polymerization – ROMP and acyclic diene metathesis – ADMET. This motivates the investigations into the development of new, efficient, stable, and highly selective catalytic systems based on ruthenium complexes
Several methods have been reported for the synthesis of 2-(N,Ndialkylaminomethyl)styrenes [39-46] relying on different approaches: i) from o-vinylbenzyl chloride [43], ii) by the Hofmann cleavage of quaternary tetrahydroisoquinoline salts under the action of silver oxide [39,42] and iii) by a reaction of 2-(2-bromoethyl)benzyl bromide with secondary amines under microwave irradiation followed by the decomposition of the products under the action of potassium tert-butoxide [46]

Summary

Introduction

Ruthenium-catalysed olefin metathesis reactions have been playing an important role in various fields of organic synthesis in the past three decades. The present work opens a series of studies by our group, which will be devoted to the synthesis and reactivity of Hoveyda–Grubbs-type catalysts possessing a six-membered ruthenium-containing ring with the N→Ru, S→Ru, and Se (Te)→Ru coordinate bonds. Scheme 1: Efficient multigram synthesis of N,N-dialkyl-2-vinylbenzylamines 4 (R1X = Me2SO4, Et2SO4 or BnCl, see Experimental part, Supporting Information File 1 and Table 1).

Results

Conclusion