Nitrene insertion, transition metal

The transition metal-catalyzed C-H insertion reaction of carbenes to organic compounds is a well-established synthetic method, as shown in the first two sections in this chapter. However, nitrene C-H insertion, the corresponding reaction of carbene analog, is much less known. In the past decade, considerable advances have been made in the development of this chemistry into a generally useful C-H amination process by using improved catalysts and protocols, in which readily available amines or amides are used as the starting substrates. Moreover,... 

P, Miiller, Transition Metal-Catalyzed Nitrene Transfer Aziridination and Insertion, in Advances in Catalytic Processes, Vol. 2, M. P. Doyle, Ed., JAI Press, Greenwich, CT, pp. 113/. 

Attempts to achieve asymmetric nitrene insertion reactions catalyzed by chiral transition metal complexes have also been performed [41,42]. The reaction of the nosyl-imine derivative as the nitrene donor with indane 61 catalyzed by the chiral rhodium complex 63 gave the optically active allyl amine 62 in good yield and moderate ee (Eq. (15)) [41],... 

The phosphides and arsenides of the elements M—PRR and M—AsRR are well known for main group elements, but transition metal analogues are more unusual. Insertion reactions were not widely explored until recently, but examples are given in reactions (j) and (k) (X = O or S) ° and (l) (n) (X = or As ) and (m) are effectively oxidative insertions of a nitrene, or specifically PhN into an Sn-P or Sn-As bond, and thus represent an extension of the Staudinger reactions whereby a phosphine or arsine is treated with an azide, and thereby converted into a phosphine-imine or the arsine analogue, as follows ... 

The electron-deficient sulfonyl nitrene (88) can insert into electron-rich carbon-hydrogen bonds, abstract hydrogen atoms, and add to double bonds and aromatic rings. These reactions may be initiated by acids, heat, light and transition metals. The reactions are illustrated by heating methanesulfonyl azide (89) with bezene (23) (Scheme 59). Here, the electrophilic sulfonyl nitrene (90) adds to the electron-rich aromatic double bond, but the kinetically favoured azepine(91) rearranges to give the thermodynamically favoured N-phenyl sulfonamide (92) (Scheme 59). 

Breslow R, GeUman SH (1983) Intramolecular nitrene C-H insertions mediated by transition-metal ctnnplexes as nitrogen analogues of cytochrome P-450 reactions. J Am Chem Soc 105 6729-6730... 

C-H insertion reactions of carbenes and nitrenes assisted by transition metals have been overviewed. Transition-metal-catalysed carbenoid insertions as a tool for C-H functionalization have been detailed. The intermolecular versions of these C-H insertions have been discussed from the point of view of their mechanisms and stereochemical outcomes. ... 

Like carbenes, nitrenes also insert into C-H bonds and add to double bonds. In some of the most useful nitrene addition reactions, however, free nitrenes are not involved rather a carrier such as a transition-metal complex or an iodine or bromine reagent is... 

Chanda, B. M., Vyas, R. and Bedekar, A. V. 2001. Investigations in the transition metal catalyzed aziridination of olefins and insertion reactions with bromamine-T as the source of nitrene. J. Org. Chem. 66 30-34. 

Chair-like transition states minimizing gauche interactions between the substituents with metal nitrene insertion into the equatorial C-H bond are used to explain the stereochemical outcome. Such an intramolecular C-H amination with sulfamates was used in a few syntheses, including the total synthesis of (-l-)-sax-itoxin [66, 67]. 

The active nitrene intermediate should insert into a saturated C-H bond [8], excluding also that reaction 27 proceeds via the corresponding N-(2-aminobenzoyl)amidc. Nucleophilic nitrene complexes are known to react with the carbonyl group of aldehydes and ketones to yield the corresponding imines and a metal-oxo complex [91], However, the driving force of this reaction is the oxophilicity of early transition metals used in [91], whereas the catalyst used in this work are derivatives of the late-transition metals. Oxo derivatives of these metals in the low oxidation state are ver> rare. The mechanism followed by this reaction requires further investigation in order to be clarified. 

While major advances in the area of C-H functionalization have been made with catalysts based on rare and expensive transition metals such as rhodium, palladium, ruthenium, and iridium [7], increasing interest in the sustainability aspect of catalysis has stimulated researchers toward the development of alternative catalysts based on naturally abundant first-row transition metals including cobalt [8]. As such, a growing number of cobalt-catalyzed C-H functionalization reactions, including those for heterocycle synthesis, have been reported over the last several years to date (early 2015) [9]. The purpose of this chapter is to provide an overview of such recent advancements with classification according to the nature of the catalytically active cobalt species involved in the C-H activation event. Besides inner-sphere C-H activation reactions catalyzed by low-valent and high-valent cobalt complexes, nitrene and carbene C-H insertion reactions promoted by cobalt(II)-porphyrin metalloradical catalysts are also discussed. 

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