C-H Amination with Rhodium II Catalysts

NHNs insertion with complete retention of stereochemistry 

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Intramolecular C-H Amination with Rhodium(II) Catalysts 391 Tab. 17.2 Rhodium-catalyzed insertion of sulfamates. 

Intermolecular amination experiments described by Muller using 02NC,5H4S02N=IPh (NsN=IPh) as the nitrene source underscore the value of certain rhodium(II) catalysts for C-H insertion (Scheme 17.5) [12, 34—36]. In accord with Breslow s finding, dirhodium carboxylates were demonstrated to catalyze the amination of allylic, benzylic, and adamantyl substrates. Notably, structurally related tetracarboxamide dimers fail to give... 

Asymmetric C-H amination has progressed through the apphcation of rathenium(II) porphyrin catalysts. Che has employed fluorinated ruthenium porphyrin complexes with added AI2O3 (in place of MgO) to catalyze suifamate ester insertion (Scheme 17.31) [98]. These systems show exceptional catalyst activity (>300 turnovers) and afford product yields that are comparable to rhodium tetracarboxylate-promoted reactions. Of perhaps greater significance is that the use of the chiral rathenium complex... 

C-H alkylation and amination reactions involving metal-carbenoid and metal-nitrenoid species have been developed for many years, most extensively with (chiral) dirhodium(ll) carboxylate and carboxamidate complexes as catalysts [45]. When performed in intramolecular settings, such reactions offer versatile methods for the (enantioselective) synthesis of hetero- and carbocy-cles. In the past decade, Zhang and coworkers had explored the catalysis of cobalt(II)-porphyrin complexes for carbene- and nitrene-transfer reactions [46] and revealed a radical nature of such processes as a distinct mechanistic feature compared with typical metal (e.g., rhodium)-catalyzed carbenoid and nitrenoid reactions [47]. Described below are examples of heterocycle synthesis via cobalt(II)-porphyrin-catalyzed intramolecular C-H amination or C-H alkylation. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Allyl amines and alkynes were explored as starting materials for pyridines synthesis by Jun and coworkers as well [109]. The reaction proceeded through a sequential Cu(II)-promoted dehydrogenation of the allylamine and Rh(III)-catalyzed iV-annulation of the resulting a,/3-unsaturated imine and alkyne. Moderate to good yields of pyridines can be isolated (Scheme 3.52). This transformation was later on explored with ruthenium catalyst [110]. In the presence of [ RuCl2(p-cymene) 2] (0.1 equiv.), KPFe (0.1 equiv.), and Cu(OAc)2 (1 equiv.) in tAmOH at 100°C, the desired pyridine derivatives were formed in good yields. In this case, the reaction started with C-H activation and then insertion to alkynes which is different from the rhodium catalyzed case. 

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