Cleavage carbon-nitrogen bonds

The formation of 2H-pyrroles (21) and a pyrrole derivative (22) from the reaction of 3-phenyl-2//-azirines and acetylenic esters in the presence of molybdenum hexacarbonyl is intriguing mechanistically (Schemes 24, 25).53 Carbon-nitrogen bond cleavage must occur perhaps via a molybdenum complex (cf. 23 in Scheme 26) but intermediate organometallic species have not yet been isolated.53 Despite the relatively poor yields of 2H-pyrrole products, the process is synthetically valuable since the equivalent uncatalyzed photochemical process produces isomeric 2H-pyrroles from a primary reaction of azirine C—C cleavage54 (Scheme 24). 

Novel synthetic procedures for indolizidine alkaloids were developed via a samarium diiodide-promoted carbon-nitrogen bond cleavage as a key step. Application of the procedure led to the total synthesis of (+)-(8R, 8aR)-perhydro-8-indolizidinol <2006H193>. 

Ketones containing sulfur or nitrogen atoms bound to a-carbons suffer carbon-sulfur or carbon-nitrogen bond cleavage under the conditions of the Clemmensen reduction [159, 864 (p. 118). A ketosulfone was reduced to a sulfone-alcohol with zinc in refluxing 80% acetic acid in 70% yield [920]. 

Effect of 2,6-substituents on the carbon-nitrogen bond cleavage rate in radical-zwitterions from 1 -benzyl-4-phenylpyridiniums in dimethylformamide at 25 °C. 

The electrochemical cyclization reaction is less successful with the N-(3-phenylallyl)acetanilide 60 which has two potential bond cleavage sites from the radical-anion [173]. Carbon-nitrogen bond cleavage with loss of a 3-phenylallyl radical, leaving an amide nitrogen anion, is favoured over carbon-chlorine bond cleavage. 

Except in two isolated cases, in which Af,Af-dimethylaniline was transformed into N-methylaniline and Ai-(diphenylmethyl)benzotriazole gave a mixture of products (using biphenyl or DTBB as the electron carrier, respectively), the reductive carbon-nitrogen bond cleavage has always been applied to amides and their derivatives. 

The reaction rate constant for carbon-nitrogen bond cleavage in nitrobenzene has been determined to be ... 

Kadin, S. B.. Monomethylation of aromatic amines via sodium borohydride. Mediated carbon-nitrogen bond cleavage, 7. Org. Chem.. 38, 1.348, 1973. 

Vinylaziridines such as (162) have been rearranged theimally to 3-pynolines (equation 51),presumably through one of the species (164). Substituents play an important role in the likelihood of these inteim ates. The energy of activation for carbon-nitrogen bond cleavage has been estimated to be 12-14 kcal mol" (compared with 27 kcal mol for cyclopropane). Vinylaziridines of type (165 R = alkyl) furnish 1-pyirolines (166) or, if X is another heteroatom, the corresponding heterocyclopentenes (equation 52 Section 8.1.7). - ... 

Heterolytic carbon-nitrogen bond cleavage is responsible... 

Sultams like (190) undergo aminolysis with amines by nitrogen-sulfur bond cleavage (similar to hydrolysis), and suitably functionalised sultams (191) may also suffer carbon-nitrogen bond cleavage by a bimolecular (E2) elimination reaction (Scheme 79). 

When heated with benzene in the presence of AICI3, OOiV-trialkyl phosphoramidates suffer both carbon-oxygen and carbon-nitrogen bond cleavage, and afford mono- or di-alkylbenzenes. When, on the other hand, 00-diphenyl iV-(cyclo)alkyl phosphoramidates or AWW"-trialkyl phosphoric triamides are employed, only carbon-nitrogen bond cleavage takes place, and no reaction occurs with most amides from secondary amines. ... 

Reductive deamination of pyrrolidine (3) with samarium diiodide in THF-HMPA in the presence of methanol as the proton source yielded the desired piperidone (4) stereoselectively in 90% yield (Eq. (2)), where a carbon-nitrogen bond cleavage reaction and subsequent recyclization took place simultaneously (05TL5161). 

I.I.4. Schiff Base and Other Reactions Involving Carbon-Nitrogen Bond Cleavage... 

The binding of the carbonyl oxygen of amides to zinc(II) of carboxypeptidase is based on X-ray studies of enzyme-inhibitor complexes. Of course, the amides studied may be inhibitors because they bind to the enzyme incorrectly. An alternative mechanism, which makes chemical sense, could involve metal-ion coordination to the amide nitrogen which would not only stabilise the tetrahedral intermediate (XVI) but also facilitate carbon-nitrogen bond cleavage. Such a mode of catalysis... 

Though carbon-nitrogen bond cleavage reaction is less explored, allylic C-N bond can be cleaved by low valent late transition metal complexes. Treatment of (/x-dinitrogen or carbon dioxide)nickel(O) complexes with allylammonium... 

Aliphatic and aromatic amines are also widely available from nature or industry. However, studies on their chemical transformation through transition metal-catalysed carbon-nitrogen bond cleavage are relatively scarce. Recently, several nickel-catalysed transformation of amine derivatives including aryl or benzylammonium salts, N-atyl amides and carbamates, as well as JV-sulfonyl aziridines were reported. 

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