Imine compounds heterocyclic rings

Nitrile imines have been added to 1,4-diazepines (246) (143,144), 1,2, 4-triazepines (247) (145), 1-benzazepines (248) (146), 1,4-benzodiazepines (249-251) (147-149), 1,5-benzodiazepines (252, 253) (X = NH) (143,150-153), 1,5-benzothiazepines (253) (X=S) (153). Interest in this area has been stimulated by the known pharmacological activity of many compounds with five-membered heterocyclic rings fused to a benzodiazepine skeleton. 

This methodology is applicable to the synthesis of biologically important compounds. For example, imines A and B in Scheme 1.107 having a heterocyclic ring are reduced with... 

Typical UV spectra of some pyridine V-imines are summarized in Table III. The spectra of the V-imines unsubstituted in the heterocyclic ring contain two transitions near 230 and 320 nm18 which are strongly dependent on the solvent. In addition, ring-substituted compounds show absorption at 270 nm. In the same solvent, the position of the absorption bands is only slightly dependent on the substituent of the imino group, with the exception of the V-arylimines.38 70 71 The azomethine imine system of the V-imines is apparently the essential chromophore since these compounds show analogous absorption frequencies (for a summary of azomethine imines see Timpe.m)... 

As previously pointed out, heteroaromatic A-imines contain the structural element of an azomethine imine. A typical reaction of this class of compound is 1,3-dipolar cycloaddition.121139 In heteroaromatic A-imines, such reactions are difficult since they involve loss of the aromaticity of the heterocyclic ring. Factors essential to the success or failure of a 1,3-dipolar reaction are the aromatic character of the parent heterocycle, the electron effect of the substituent R, and the nature of the dipolarophile. 

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organonitnles arises both from the reactivity of the C=N bond, and from the abiHty of the cyano substituent to activate adjacent bonds, especially C—H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxyHc acids and esters, aldehydes, ketones, large-ring cycHc ketones, imines, heterocycles, orthoesters, and other compounds. Some of the more common transformations involve hydrolysis or alcoholysis to produce amides, acids and esters, and hydrogenation to produce amines, which are intermediates for the production of polyurethanes and polyamides. An extensive review on hydrogenation of nitriles has been recendy pubHshed (10). 

Relatively little data are available on sulfonamido derivatives of heterocyclic systems with five-membered rings. The tautomeric equilibrium between structures 222 and 223 has been shown to favor the imine form by about 10 1 by comparison of the ultraviolet spectrum of the parent compound with those of both methylated forms." ... 

Other advances include the construction of seven- and nine-membered rings via the analogous [4-1-3] and [6-1-3] cycloadditions with dienes and trienes respectively. Heterocycles, such as tetrahydrofurans and pyrrolidines, are accessible using carbonyl compounds and imines as substrates. The following discussion is organized around these recent discoveries. It serves to illustrate the versatility and the high degree of selectivity which are some of the distinctive features of the Pd-TMM chemistry. 

Closure of the oxadiazole ring is still achieved through cycloaddition between pyridine iV-oxides and isocyanates, affording adducts such as 142 (Scheme 38) <1995T6451>. Nonaromatic imine fV-oxides exhibited similar reactivities, since azasugar-derived fV-oxides as a mixture of 143 and 144 underwent cycloaddition reactions in the presence of phenyl isocyanate or trichloroacetonitrile. Compounds 145 and 146 (Scheme 39) were obtained from the aldoxime W-oxide 143 two other regioisomeric heterocycles arose from the ketoxime derivative 144 <1996T4467>. 

Electric dipole moment studies have provided excellent support for the formulation of certain heterocycles as mesoionic compounds. Hanley et al. <78JCS(P1)600> have measured dipole moments for mesoionic l,2,3,4-thiatriazol-5-imines (20), 5-ones (21) and 5-ylidenemalononitriles (22) using a vector analysis similar to that previously employed for sydnones and other mesoionic compounds assuming that mesoionic rings are regular pentagons. The dipole moment of 3-phenyl-1,2,3,4-thiatriazolium-5-anilide (20) was found to be 3.71 D and five derivatives of compounds (21) were measured and the ring moment calculated to be 3.8 D. In both cases the dipole moments are rather small but clearly consistent with the mesoionic formulation. 3-Phenyl-l,2,3,4-thiatriazolium-5-dicyanomethanide (22) was found to have a dipole moment of 8.84 D. 

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