Cis-Imidazolines

Other cis-imidazoline derivatives of the current invention were prepared by the author in an earlier investigation (2). 

Imidazolines and isoxazolines. 1,3-Dipolar cycloaddition of isocyanoacetic esters and amides with 7/-tosylimines and aldehydes, respectively, furnishes the five-membered heterocycles. Interestingly, cis-imidazolines and frans-oxazolines are major products. Since trans-imidazolines are obtained on base-catalyzed isomerization of the cts-isomers, both erythro- and threo-a,P-diamino acids are accessible. 

The formation of derivatives of 2,3,6,8-tetraazabicyclo-[3.2.1]3-octene (425) arises from an intramolecular nucleophilic addition to the nitrone group of hydra-zone (424). Compound (424) was prepared by reaction of 2-acyl-3-imidazoline-3-oxides (423) with hydrazine. From the cis- and frans-derivatives (424), exo- and enr/o-isomers (425) were obtained (Scheme 2.197). The reaction of intramolecular cyclization does not occur in cases with monosubstituted hydrazones (316). 

For example, complex 37 with an imidazolin-2-ylidene and a methyl ligand in cis-position to each other decomposes to yield the 1,2,3-trimethylimidazolium salt 38, Pd°, and cod (Fig. 13) [124], Additional examples for the reductive elimination of 2-alkyl and 2-aryl substituted azohum salts from palladium or nickel NHC complexes have been reported [125, 126]. Today, reductive elimination reactions have been established as one important reaction pathway for the deactivation of catalytically active metal NHC complexes [126, 127]. 

Another reaction pathway is observed in methanol [117]. Irradiation of a methanolic solution of 134 led to imidazoline 147 in 60% yield, with a possible intermediate being azomethine ylide 146 (Scheme 1.44). However, two pathways for the formation of imidazoline 147 are possible. The first one is via initial formation of an enediimine 141 (such reaction is known as a nonphotochemical process [118, 119]). The fact that addition of methanol to compound 141 obtained by irradiation of cis-d i h yd ro pyrazine or trans-dih yd ro pyrazi ne 140... 

W L = l,3-dimethyl-4-imidazoline-2-ylidene). The thermodynamically less stable trans isomers reconvert thermally to the cis-complexes (98,99) (Fig. 8). 

The greater reactivity of 2-ethoxy-2-imidazoline-l-carboxylic acid over 1-carboxy-2-imi-dazolidinone in aqueous alkali to decarboxylation has been ascribed to tautomeric protonation of N-3 in the former <82TL659>. Irradiation of either the cis or trans forms of 2,4,5-triphenyl-2-imidazoline gives a mixture in which the trans form (131a) predominates <75BCJ3669>. 

The reaction of 3-amino-l-phenyl- and 3-amino-l(thien-2-yl)-4,4,4-tri-fluorobut-2-en-l-ones with 1,2-diaminopropane and l,2-diamino-3,3,3-trifluoropropane under kinetic control conditions (room temperature, 20 h) forms a mixture of cis and trans isomers of imidazolines, one of which prevails (isomer ratio 9 1) (99IZV2135,... 

Cyclization of imidazolones 638 with thiourea under dry conditions using MWI for 8-9 min, gave the cis- and tranj-isomers of thioxopyrimido[4,5-J]imidazolines 639 and 640 in 76-80% and 10-18% yields, respectively. Also, the cyclization with cyanoguanidine under MWI for 7-8 min produced the isomeric cis 641 (75-80%) and trans 642 (13-15%) of iminoxypyrimido[4,5-J]imidazolines (Scheme 125). The cyclization under conventional heating required 3-5 h to give the cis- and trans-isomers in 50-58% and 11-22% yields, respectively (01S1509). 

Another series of chiral Ci-symmetric monodentate ruthenium complexes 151-154 reported by Collins and coworkers contained bulky ferf-butyl units on the imidazoline ring and unsymmetrical nitrogen substitution, having one JV-aryl and one JV-methyl group (Figure 11.31) [114]. 

C12 2 Cl20i,PdS2, cis DichlorO (4,7,13,1 6-tetraoxa-1, 1 0-dithiacyclo-octadecane)palladium(II), 4OB, 1005 C12 2 ftCuNgOsSft, Tetrakis(imidazoline-2-thionato)copper(I) nitrate, 42B, 936... 

The structure of natural d-biotin (cis-tetrahydro-2-oxothieno[3,4-d]imidazoline-4-valeric acid) is as follows ... 

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