Organic imines

The first tantalum nitrene was obtained in 1959 by thermolysis of [Ta(NEt2)]5-288 This class of compounds is presently accessible by several routes, including hydrogen abstraction from the mono- or di-alkylamides, reaction of metallacarbenes with organic imines, oxidation of low valent species by organic azides, or reductive coupling of nitriles (Table 13). The tantalum derivatives are usually stabler than those of niobium. 

Chlorocyclophosphazenes react with organic acids or their salts (21, 346, 448), acid amides (206), and acid halides (207) to yield the nitrile of the acid the phosphazene ring is degraded. The reaction of benzoyl chloride with [NP(OEt)2]3 4 gives ethyl chloride, ethyl phos-phenates, and triphenyl-s-triazine (188). The trifluoroethoxy derivatives, [NP(OCH2CF3)2]3 4, react with diphenyl ketone to afford the acid, (CF3CH20)2P(0)(0H), and organic imines (405, 406). 

The reactions of the alkoxycyclophosphazenes [NP(OCH2CF3)a]3,4 with diphenyl ketone result in the formation of the acid (CF8CHa0)2P(0)(0H) and organic imines. > The cyclophosphazene N3P3CI6 (and N4P4CI8) reacts with formamide and thioformamide to give metaphosphimic and metathiophos-phimic acids, respectively. These acids appear to be in tautomeric equilibrium, e.g. 

Metathesis reactions have also been used to prepare imido compounds. In one such metathesis reaction, an 0x0 complex reacts with an isocyanate to form an imido complex (Equation 13.59). In another case, a carbene complex reacts with an organic imine to form the corresponding olefin and a transition metal-imido complex (Equation 13.60). ... 

R.A. Sheldon and J.K. Kochi, in Metal-Catalyzed Oxidations of Organic Compounds, pp. 324-325, Academic Press, New York (1981). The observation that the yield of the organic imine product never exceeded 50% based on metal suggests the possibility that the last step in the product formation is a bimolecular process requiring a second equivalent of metal oxidant. 

In addition to their antiknock properties, organic lead compounds possess bactericidal properties and motor fuels with lead are known to inhibit bacterial growth during storage in contact with water. With the disappearance of lead-based compounds, it is necessary to incorporate biocides from the cyclic imine family, (piperidine, pyrrolidine, hexamethyleneimine), alkylpropylene diamines or imidazolines (Figure 9.2). 

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. 

This area of research has only recently attracted the attention of synthetic organic chemists, but there has been a flurry of impressive activity in the area. Simple (i. e., unstabilized) carbenes suffer from many of the problems of nitrenes (vide infra) and most reported synthetically useful procedures use carbenoids the majority of recent reports have focussed upon reactions between a-diazoesters and imines in the presence of a range of catalysts. In one of the earliest reports of enantioselective carbene-imine reactions, for instance, Jacobsen and Finney reported that ethyl diazoacetate reacts with N-arylaldimines in the presence of cop-per(i) hexafluorophosphate with mediocre stereoselectivity to give N-arylaziridine carboxylates. Though the diastereoselectivities of the reaction were often acceptable (usually >10 1, in favor of the cis isomers) the observed enantioselectivity was low (no more than 44% ee Scheme 4.27) [33],... 

TV-aluminum imines are another example of masked inline derivatives of ammonia. They are easily synthesized by partial reduction of nitriles with diisobutylaluminum hydride (D1BAL-H)6. Addition of lithium organic reagents to /V-aluminum iniines 7 derived from O-protected cyanohydrins 6 provides a-amino alcohols 8a and 8b in moderate yields and low to good diastereo-selectivities n 12. 

Lanthanide triflates catalyze the Diels-Alder reaction of imines, generated from anilines and aldehydes, with both dienes and alkenes [26]. Thus N-benzyl-ideneaniline in the presence of Yb(OTf)3 (Scheme 6.16) reacts in organic solvent with open-chain dienes, such as Danishefsky s diene, to give tetrahy-dropyridine derivatives, while with cyclopentadiene and vinylethers and vinylthioethers it works like azadiene in both organic solvent and aqueous medium, affording tetrahydroquinoline derivatives. 

This approach finds experimental support in FTIR measurements of the oxidation of PANI in organic solvents which indicate an anion intercalation mechanism for the second oxidation step. However, the IR findings may also be interpreted as support for the formation of a protonated imine structure... 

A series of complexes in which the cyanide ligands are modified or replaced arises from the decomposition of methyl and pyridiomethylcobalt(111) pentacyanide derivatives in acid solution. The reactions include protonation of a cyanide ligand, insertion of a cyanide ligand between the organic group and the cobalt atom to produce an imine (see Section VI,D), decomposition of this imine to an acyl product, and replacement of a cyanide ligand by water 100, 101). The products are listed in Table III, 29. 

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