Imines heterocyclic

The reactions of nucleophiles with complexes of chelating heterocyclic imines a critical survey. E. C. Constable, Polyhedron, 1983, 2, 551-572 (185). 

A few heterocyclic imines reacted poorly if at all with chromium alkoxycarbene complexes. Oxazines required the use of the more reactive (and less stable) molybdenum alkoxycarbenes, producing oxacephams in -40% yield. Oxazo-lines gave low yields (-12%) of the oxapenam system, along with similar amounts of oxazinone, resulting from incorporation of two equivalents of ketene (Eq. 3) [20]. 

Table 3 Reaction of chromium alkoxycarbenes with chiral heterocyclic imines ...

Ethylenimines or aziridines [lb] can be considered cyclic imines and are only briefly covered in Section 5. The preparation of heterocyclic imine systems, semicarbazones, hydrazones, azines, and oximes, is omitted from this chapter. The synthesis of carbodiimides is presented in Chapter 9. 

The acidity of the Os(III) ammine complexes is enhanced considerably by replacement of an ammine ligand by N-heterocyclic, imine, or... 

The cycloaddition of diazomethane to SchifT bases from heterocyclic aldehydes and anilines provides a useful route to heterocyclic substituted triazolines. Unlike olefins bearing heterocyclic substituents, the heterocyclic imines can be obtained readily by reaction of the appropriate aldehyde and amine thus the diazomethane-imine addition has greater scope than the olefin-azide reaction. NMR spectroscopic studies of the orientation of addition are in accord with previously reported mechanistic considerations (see, e.g., Scheme 93).329 In addition to the influence of the N-aryl group, the electron-withdrawing power of the heterocyclic substituent on the Schiff-base carbon also has a substantial effect on imine reactivity, in the order 2-quinolyl 2-, 3-, or 4-pyridyl > phenyl > 2-thienyl as 2-furyl.329... 

Substituted benzylideneanilines form molecular complexes187 with 106 and with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (110) (chloranilic acid). These complexes were investigated by IR and 111 NMR. The complexes between benzylideneanilines and 106 are CT complexes (111), while complexes with 110 are formed through electron and proton transfer187, as illustrated in 112. In 111, a refers lo n -> jr interaction and b is a jr -> jr interaction, sp2 N-atoms of some heterocyclic imines (such as 2,2 -bipyridyl, 1,10-phenantroline) are also n-donors towards acceptors (tetracyanoethylene, p-benzoquinone, chloranil)188. 

The following two synthetic techniques are applied for obtaining complexes of aliphatic, aromatic, and heterocyclic imines in the limits of the discussed variant of the template synthesis interaction of coordinated mono- and diamines with mono- and dicarbonyl derivatives (method A) and reactions of complexes of o-hydroxyalde-hydes (ketones) with amines and diamines (method B). The simplest transformation of this type is represented by the reaction (3.176) [53,54] ... 

Silver is well known in its ability to oxidize amines into imines or hydroxyl-amine compounds. Normal conditions use persulfate as an oxidant, with the mechanism considered to be a radical chain reaction (87-93). In some cases, oxidative condensations may occur between two substrate molecules to yield heterocycles. Imines can be oxidatively converted into aldehydes or ketones with aldehydes eventually converting into carboxyhc acids. In 1999, Enders and co-workers (94) reported the mild oxidation of a-amino nitriles into a-hydro-xyenones. The reaction was regioselective with good reported yields. 

The first highly diastereoselective hydrophosphonylation of heterocyclic imines, 3-thiazolines (330) by a chiral phosphorus reagent BINOL, has been performed. The relative configuration of BINOL and the newly formed stereogenic centre in the a-amino phosphonic acid derivatives (331) have been elucidated by X-ray analysis. 

The first efficient enantioselective synthetic route to cyclic a-amino phosphonates, namely the pharmaceutically interesting heterocyclic phosphonates of type 1 [63,64],by an asymmetric addition reaction of dialkyl phosphites to heterocyclic imines was recently developed by Shibasaki et al. (Scheme 23) [ 10,77]. 

A further application of 1,3-dipolar additions to the synthesis of seven-membered rings is cycloaddition to the C=N double bond of 1,5-benzothiazepines. In an extension of their investigations into the cyclofunctionalisation of heterocyclic imine systems, Chimirri et al. have demonstrated that the cycloaddition of benzonitriloxide to 1,5-benzothiazepines affords 3a,4-dihydro-l-phenyl-5//-... 

It is well known that alkyl azides also behave as 1,3-dipoles in intramolecular thermal cycloaddition reactions. The formation of two carbon-nitrogen bonds leads to triazolines, which are usually not stable. They decompose after the loss of nitrogen to aziridines, diazo compounds, and heterocyclic imines. There are a limited number of examples reported in which the triazoline was isolated [15]. The dipolar cycloaddition methodology has been extremely useful for the synthesis of many natural products with interesting biological activities [16], In recent years, the cycloaddition approach has allowed many successful syntheses of complex molecules which would be difficult to obtain by different routes. For instance, Cha and co-workers developed a general approach to functionalized indolizidine and pyrrolizidine alkaloids such as (-i-)-crotanecine [17] and (-)-slaframine [18]. The key step of the enantioselective synthesis of (-)-swainsonine (41), starting from 36, involves the construction of the bicyclic imine 38 by an intramolecular 1,3-dipolar cycloaddition of an azide derived from tosylate 36, as shown in Scheme 6 [ 19). 

Baugh et al. [22] synthesized and characterized a series of nickel(II) and iron(II) complexes of the general formula [LMX2] containing bidentate (for M = Ni) and tridentate (for M = Fe) heterocycle-imine ligands. Activation of these pre-catalysts with methyl aluminoxane yields active catalyst systems for the oligomerization/polymerization of ethylene. Compared to a-diimine nickel and bis (immo)pyridine iron catalysts, both metal systems provide only half of the steric protection and consequently the catalytic activities are significantly lower. 

Among the depicted reactivity modes, we are particularly interested in the reactions of DCA that is accounted as an alternative route for the generation of heterocyclic imines (Route I) and A-heterocyclic carbenes (Route II). While the reactions of the metal-mediated DCA to nitriles have been extensively reviewed circa 10 years ago [1], over the past decade, many new reactions illustrating this approach have appeared. In addition, previously unknown examples for [2 - - 3] DCA to isocyanides have emerged. In this survey, we describe the recent trends in metal-mediated transformation of CN substrates via the reactions of [2 - - 3] DCA exemplified by the most representative papers. The mechanistic features and driving forces of these processes as well as the reasons of activation effect upon coordination of substrate to the metal center are also discussed. 

Heterocyclic imines with a thiomethyl group adjacent to nitrogen are in equilibrium with ketene 5,Af-acetals. On reaction with aryl isocyanates, linear 1 1 adducts 95 are obtained. ... 

A comparison of the reaction products obtained from RCH=NPh (R = MeO, Ph, PhCH=CH) and two heterocyclic imines with ketenes, generated by photolysis of oxazolidine- and oxazolidinone-chromium carbene complexes and from the oxazolidi-none carboxylic acid chlorides, indicated high yields and high diastereoselectivities in some of these reactions... 

Several other recent reviews contain material relevant to this section. An article by Blandamer and Burgess on the thermodynamics, kinetics, and mechanisms of solvation, solvolysis, and substitution in nonaqueous solvents contains a contribution on the controversial dissociative mechanism for isomerization of square-planar molecules. This is outlined in Section 5.5. A review of ligand substitution reactions at low-valency transition-metal centers contains sections on five-coordinate metal carbonyl complexes and on ML4 complexes (mainly tetrahedral configurations with L being a tertiary phosphine), as well as on acid- and base-catalyzed reactions. A review by Constable " surveying the reactions of nucleophiles with complexes of chelating heterocyclic imines contains a sizable section on square-planar palladium and platinum derivatives. Most discussion centers on [Pt(bipy)2] and [Pt(phen)2] (bipy = 2,2 -bipyridine phen = 1,10-phenanthroline). The metal center, ligand, or both are susceptible to nucleophilic attack and the mechanisms involved are critically assessed. 

The anions derived from 2,4,4,6-tetramethyl-5,6-dihydro-l,3-oxazine have been used as the basis of several general synthetic procedures. Alkylation of the anion followed by reduction of the heterocyclic imine group and hydrolysis gives aldehydes. ... 

---