C-N Insertion

In the dihapto mode the pyridine ring can be protonated intermolecularly at nitrogen, or even intramolecularly deprotonated at carbon. The first evidence for metal C—N insertion is the reaction of the metallaaziridine complex (111) with homogeneity LiHBEt3 in THF at low temperature that yields (112) (Scheme 49).251-254 Experiments with carbon nucleophiles (RMgCl, MeLi) in place of LiHBEt3 have provided valuable information to allow discrimination between... 

An interesting case of metal-assisted ring opening of (109) has been described by Wolczanski using the low-valent (silox)3Nb fragment that binds (109) in the //2(N,C) mode (Scheme 50). Derivative (113) undergoes C—N insertion by thermolysis in benzene at 70 °C only. The reaction gives 0.5 equiv. of (109) and 0.5 equiv. of (114) as a thermodynamic mixture of cis,cis-, trans,cis-, trans,trans- and cis,trans-isomers.255-257... 

At low temperatures cyclopropenones and enamines or ketene acetals were shown to yield 2-azonia-bicyclo(3,l, 0)hex-3-enolates-3 (371, X=0), which can be isomerized thermally to penta-2,4-diene amides(372, X=0). At elevated temperatures the amides were found to be the principal products arising from C-N-insertion 237) (insertion of the cyclopropenone three-carbon unit into the C-N bond of the enamine). These were accompanied in some cases by 3-aminoenones 373 arising from C-C-insertion 237) (insertion of the cyclopropenone into the C-C double bond of the enamine) and a-amino cyclopentenones 375 formed by Stevens rearrangement of the ylide 369 and cyclopentenones 374 ( condensation 237)). 

The products formed in the reaction of diphenylcyclopropen-one or -thione and 1-methyl-2-methylthiopyrroline have been shown to be the l,2,7,8-tetrahydroazocin-2-one (87) and the thione, respectively, evidently arising from a C,N-insertion pathway involving an ylide rearrangement (72HCA1759). 

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... 

The bis(ir-allyl) complex derived from the linear dimerization of butadiene can be trapped with phe-nylhydrazones in a process involving C—N insertion into a ir-allyl intermediate.265 Predominant insertion into the more substituted terminus is observed (equation 304). 

J. Kim, BAl. Stoltz, A C-N insertion of p-lactam to benzyne unusual formation of acridone. Tetrahedron Lett. 53 (2012) 4994-4996. 

Recently, Qian and Dong disclosed a highly efficient Rh-catalyzed three-component reaction of imines, alkynes, and aldehydes via C-H activation to afford highly fused polycyclic sultam skeletons [24]. This strategy allows the formation of four new bonds in a simple-to-perform, single-operation cascade of C-H activation/C=N insertion, C-H activation/C=0 insertion, and cyclization (Eq. (5.39)). 

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