Insertion oxygen into nitrogen-carbon

Peroxyacetic acid Insertion of oxygen into nitrogen-carbon bonds... 

Facile isocyanide insertion reactions into metal-carbon, -nitrogen, -sulfur, -oxygen, - hydride, and - halide bonds have been found to readily occur. The insertion into metal-hydrides to give stable formimidines is particularly noteworthy since corresponding formyls (—CHO) are exceptionally difficult to synthesize and tend to be very unstable. There is a great deal of interest in carbon monoxide reductions, and the instability of the intermediate reduction products has made a study of the reduction process extremely difficult. Recently, however, the interaction of isocyanides with zirconium hydrides has allowed the isolation of the individual reduction steps of the isocyanide which has provided a model study for carbon monoxide reduction (39). 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

Insertion of oxygen atom from Cpd I into the carbon-carbon double bond with formation of epoxide (Scheme Ic) reveals features characteristic for a concerted process, although formation of radical intermediates is possible in many cases. A unified description of this alternative is also provided by the two-state mechanism of catalysis by Cpd I (see the section on Hydroxylation of hydrocarbons). Essentially, the concerted oxygen insertion represents a low-spin reaction surface, whereas the distinct radical intermediate is formed on the high-spin reaction pathway. In the latter case, the carbon radical may attack the nearby heme nitrogen and modify the heme covalently. This reaction is also an important inactivation pathway of cytochromes P450 during oxidative transformations of terminal double and triple bonds. 

Carbene complexes, generated by the reaction between metal salts and diazo compounds can insert into C-H bonds in a form of CH activation (see Chapter 3 for other CH activation reactions). While early reactions involved the use of copper salts as catalysts (Schemes 8.143 and 8.144), rhodium complexes are now more widely used. In molecules such as cyclohexane, there is no issue of regioselectivity, but this issue is critical for the use of the reaction in synthesis. Both steric and electronic factors influence selectivity. Carbon atoms where a build up of some positive charge can be stabilized are favoured. Hence, allylic positions and positions a- to a heteroatom such as oxygen or nitrogen, are favoured. The reaction at tertiary C-H bonds, rather than primary C-H bonds is also favoured for the same reason, but, in this case, are also disfavoured by steric effects. Reactivity and selectivity are also influenced by both the structure of the catalyst, and the... 

Regarding carbon nucleophiles, phosphoric acids have been applied as organocatalysts in multicomponent reactions between diazo compounds, alcohols, or amines, and aldehydes, imines, or Michael acceptors [76]. Diazo compounds can be converted into the respective metallocarbenes in the presence of dirhodium (n) carboxylates complexes [77], Such intermediates can suffer a nucleophilic attack from alcohols or amines generating oxygen or nitrogen ylides that may undergo a proton shift, furnishing the respective O-H or N-H insertion products (insertion pathway. Scheme 26.14). 

In the following section we shall consider the insertion of carbon dioxide into transition nieial carbon, metal hydrogen, metal -oxygen and metal -nitrogen bonds. 

If titanium-nitrogen and titanium-oxygen bonds arc available in the same molecule, CO insertion yields carbamates [104]. If carbon dioxide has the capability (0 insert into a metal-carbon or a metal-nitrogen bond, the insertion into M-N is preferred hafnium dialkyl diarnides react with CO at room temperature to yield the carbamato derivatives HfRjfOjCNR ) [105). 

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