Nitrogen Bond Cleavage

Hofmann degradation of quaternary N-methyltetrahydroprotoberberine salts induced by methanolic alkali results in scission of ring B and, less often, 

The monophenolic discretine methiodide, by contrast, under the same conditions, yielded only the normal methine base 36.  

A requirement for cleavage of ring C is the presence of a phenolic function at C-9 or C-11 in the starting methiodide salt in addition, for the formation of a tetracyclic base such as 27, a phenol is needed at C-2. A plausible mechanism for these transformations is shown below. 

Similar secoberbine derivatives are obtained when nonphenolic tetra-hydroprotoberberines are treated with acylating agents in the presence of 

Similarly, the Birch-type reduction of various tetrahydroisoquinoline A -oxides has been reported to generate secondary amines in good yields through cleavage of the central carbon to nitrogen bridge.  

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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 only example of nitrogen-nitrogen bond cleavage promoted by lithium and a catalytic amount of DTBB (10%) in THF at room temperature was performed with alkyl and aryl azides 87. After hydrolysis, the corresponding primary amides 88 were isolated (Scheme 37). ... 

In contrast to cyclic imides, the linear imide perfluoro(Af-phenyldibutanoylamine), under relatively mild conditions, affords exclusively products resulting from acyl nitrogen bond cleavage, i.e. perfluoro -butylideneaniline) (15) and perfluorobutanoyl fluoride (16).178... 

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

Scheme 9 Nitrogen-nitrogen bond cleavage of gamma hydrazinoester 36a...

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). - ... 

The rearrangement of aromatic carbonyl arylhydrazones in polyphosphoric acid involving nitrogen-nitrogen bond cleavage is similard ... 

D. Reactions of Thiophene S,N-Ylids 1. Sulfur-Nitrogen Bond Cleavage... 

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