Amidines rearrangement reactions

Dibenzo[l,3]diazepines 9, together with amidines and benzimidazoles, are produced by a rearrangement reaction when certain A.A -diarylamide oximes 7 are treated with tosyl chloride. The intermediate 0-tosyl derivatives 8 cannot be isolated.176... 

Another curiois the rearrangement followed by cycli-zation of the azide derived from the dichloride of benzophenone (reaction 97). An example of ring opening of a triazole leading to an amidine is reaction (98)... 

The N —> N type isomerization as a special version of the amidine rearrangement was described for the 2-arylaminotetrahydro-l,3-diazepine system 102176. The reaction occurred under neutral conditions to form the rearranged products 103 in 24-83% yields (equation 42). 

The reaction depicted in equation 43 between a nitrile and a lithium amide takes place as a 1,2-addition to the cyano group. The product crystallizes as a dimer (236) in which the lithium atoms are solvated by nitrile molecules and differently bonded to the amidine moieties, as shown by XRD analysis. Low-temperature H NMR spectrum in solution points to uniform chemical environments for both the aryl groups and for the Me—Si groups, and to rapid rearrangement of the Li—N coordination structures. Acidolysis of the dimer in solution yields the corresponding amidine (237) . The crystal structure of the THF-solvated analog of 236 shows dissimilar N—Li bond lengths for the two Li atoms... 

Cyclic amidines (213) react with chlorocarbonylsulfenyl chloride to give bicyclic 1,2,4-thia-diazoles. The product isolated from this reaction depends on the mode of addition. When (213) is added to chlorocarbonylsulfenyl chloride, 3-oxo derivatives (214) are isolated via the postulated intermediate (215). Addition of chlorocarbonylsulfenyl chloride to (213) leads to 5-oxo derivatives (216), via the proposed bis(intermediate) (217) (Scheme 47) <84CHEC-I(6)463). Cyclic amidines (213) have also been treated with 1-chloro-l-phenyliminomethanesulfenyl chloride (210) to afford 2>H-1,2,4-thiadiazoles (218). The other possible product from this reaction, the 2/7-isomer (219) has been shown to be unstable, rearranging to a benzothiazole. Heterocycles (213) which have been used in this transformation include 2-aminopyridine, 3-aminopyridazine, 2-aminobenzothiazole, 2-aminopyrimidine and 2-aminothiazole (Equation (33)) <86S1027>. 

AT-Substituted amidines 74 are transformed via the carbodiimide intermediate 75 into urea derivatives 76 as shown in Scheme 34 [141]. This reaction has been performed with a variety of aliphatic and aromatic substituents and in addition to (diacetoxyiodo)benzene 3 other hypervalent iodine compounds can also be used for this rearrangement. Phenyl substituted amidines 74 (R = Ph) can lead to cyclized products of type 77. 

The reaction of a variety of liganded metal derivatives with carbodiimides give [1+2] or [2+2] cycloadducts or more complicated products resulting from rearrangement or reductive coupling reactions. Also, amidinate complexes, which are sometimes obtained in the reaction of metal complexes with carbodiimides, are included. 

Claisen rearrangement of the adduct (43) formed when a propiolate ester and an aryl aldoxime combine leads to imidazole-4-carboxylates in 61-72% yields. This reaction also proceeds by ring closure of an amidine (44 Scheme 24) (80AHC(27)241). 

Ethyl azidoformate and l-trimethylsilyl-l,4-dihydropyridine react at room temperature to give the cyclic amidine 41. Since the reaction takes place 60° below the decomposition temperature of ethyl azidoformate, it is unlikely that carbethoxynitrene intervenes, formation of the triazoline followed by a Fusco rearrangement being the more reasonable interpretation. 

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