Catalytic C —H amination

DESI Detecting intermediates (catalytic C-H amination reaction cycle) Perry eta/. [351]... 

The prevalence of literature concerning C—H activations has increased dramatically over the last decade as more and more synthetically useful and efficient methodologies have become available. Several excellent reviews on C—H activation exist, including the use of different metal catalysts, the use of C—H functionalizations in natural product synthesis, and aryl-aryl bond formations," and in catalytic C—H aminations. ... 

Mahy JP, Ciesielski J, Dauban P. Catalytic C-H amination a reaction now accessible to engineered natural enzymes. Angew Chem Int Ed. 2014 53 6862-6864. 

Perry RH, CahiU 111 TJ, Roizen JL, Du Bois J, Zare RN. Capmring fleeting intermediates in a catalytic C-H amination reaction cycle. Proc Natl Acad Sd. 2012 109 18295-18299. 

Norder A, Herrmann P, Herdtweck E, Bach T. Acyclic stereocontrol in the catalytic C—H amination of benzylic methylene groups. Org Lett. 2010 12 3690-3692. 

Collet F, Dodd R, Dauban P (2009) Catalytic C-H amination recent progress and future directions. Chem Commun 34 5061-5074... 

Preliminary efforts to examine the mechanism of C-H amination proved inconclusive with respect to the intermediacy of carbamoyl iminoiodinane 12. Control experiments in which carbamate 11 and PhI(OAc)2 were heated in CD2CI2 at 40°C with and without MgO gave no indication of a reaction between substrate and oxidant by NMR. In Hne with these observations, synthesis of a carbamate-derived iodinane has remained elusive. The inability to prepare iminoiodinane reagents from carbamate esters precluded their evaluation in catalytic nitrene transfer chemistry. By employing the PhI(OAc)2/MgO conditions, however, 1° carbamates can now serve as effective N-atom sources. The synthetic scope of metal-catalyzed C-H amination processes is thus expanded considerably as a result of this invention. Details of the reaction mechanism for this rhodium-mediated intramolecular oxidation are presented in Section 17.8. 

Catalytic intermolecular C H amination has been extensively investigated but the... 

While the majority of Rh-catalyzed C-H amination processes employ hyperva-lent iodine oxidants and sulfonamide derivatives, Lebel and coworkers have demonstrated that /V-tosyloxycarbamates will engage with catalytic Rh2(02CCPh3)4 and K2CC>3 to afford products of intramolecular C-H insertion (Fig. 22) [104, 5, 105]. Similar to Du Bois earlier work involving oxidative cyclization with 1 ° carbamates [94], the /V-tosyloxy derivatives display a strong bias for oxazolidinone formation. Selectivity trends and other mechanistic data support a reaction pathway involving a Rh-nitrene oxidant. Intermolecular amination of simple benzylic substrates... 

An oxidative iminium ion formation strategy allows the synthesis of valuable Y-aminoalkyl butenolides from readily available amines in the presence of a rhodium catalyst (Equation 11.11) [32]. 2-Triisopropoxysilylfuran reacted with the iminium ion formed in situ from catalytic C—H oxidation to afford the corresponding oxidative Mannich products. 

Nature has always been a source of inspiration for scientists. While most of research developments are centered on simulating nature, it would be worthwhile to challenge nature s ingenuity to mimic the synthetic reactions. To this end, catalytic C—H bond amination is an excellent platform for the development of a non-natural enzymatic reaction. Whereas enzymes are capable of inserting oxygen atoms into even inactivated C—H bonds, the sites into... 

Suna developed a one-pot, two-step process for the intermolecular C—H amination of indoles and other electron-rich aromatic systems. Indole 229 is converted to indolyliodonium tosylate 230 (the structure of which was confirmed by X-ray crystallography) the intermediate is stable in MeCN,dichlo-romethane (DCM), and DMSO at room temperature for at least 72 h. Upon exposure to morpholine and catalytic copper salts, aminated indole 231 is isolated in good yield. The scope of competent amines is quite broad alkyl amines, benzylic amines, anilines, and allylic amines are all tolerated.The reaction sequence also works with pyrroles, azaindoles, pyrazoles, and related systems (14JA6920). Gross and colleagues reported the first one-pot synthesis of L-7-iodotryptophan firom 7-iodoindole and serine the biotransformation uses a bacterial cell lysate that can be stored lyophilized for several months and used catalyticaUy (19 examples, 9-81% yield) (140L2622). 

The isoelectronic [Ru -Ru ] complexes are relatively more accessible, and such complexes are proving to be useful for a range of chemical reactions. This article collects the chemistry at sites trans to the [Ru-Ru] single bond. The C-H activation, C-C bond formation, acceptorless alcohol dehydrogenation, cyclo-propanation, carbenoid C-H insertion, and C-H amination reactions are covered. Reactivity studies at axial sites on [Ru-Ru] multiply bonded systems are also included because of their direct relevance in catalytic chemistry. The purpose of this article is to highlight the recent progress on the axial-site chemistry on [Ru -Ru ] platforms with intent to infuse interests for further development. 

Figure 11.8 Using DESI-MS to detect short-lived intermediates from catalytic reactions. DESI-MS setup for intercepting transient intermediates of the Rh2 esp)2-catalyzed C-H amination of adamantane [75]. Reproduced from Perry, R.H., Cahill III, T.J., Roizen, J.L., Bois, J.D., Zare, R.N. (2012) with permission of PNAS...

A few mechanistic studies have been performed by Lebel and Huard to establish the catalytic cycle of this C—H amination reactions [77]. It has been shown that the deprotonation of the N-tosyloxycarbamate does not occur in the absence of the transition metal complex. Furthermore, the nature of the leaving group does not affect the amination pathway. For instance, the regioselectivity (tertiary vs. secondary C—H bonds) for the amination of adamantane is conserved, independent of the nature of the sulfonyloxy group (Eq. (5.27)). 

Catalytic addition of carbodiimides to terminal alkyne C-H, amine N-H, and phosphine P H bonds gives a new family of propiolamidines, guanidines, and phophaguanidines (Scheme 16), which are widely nsed as ancillary ligands for stabilization of varions metal complexes. 

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