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Synthesis of 2-imidazolines

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An efficient preparation of 2-imidazolines was achieved from aldehydes and ethylenediamines in the presence of tert-butyl hypochlorite. By this method, 1,3-bis(imidazolin-2-yl)benzene and 2,6-bis(imidazolin-2-yl)pyridine, which act as chiral ligands, could be prepared directly from the corresponding dialdehydes in high yields.
M. Ishihara, H. Togo, Synthesis, 2007, 1939-1942.

A mild, environmentally friendly, and efficient process enables the synthesis of 2-imidazolines in high yield by reaction of aldehydes with ethylenediamine using hydrogen peroxide as an oxidant in the presence of sodium iodide and anhydrous magnesium sulfate.
G.-y. Bai, K. Xu, G.-f. Chen, Y.-h. Yang, T.-y. Li, Synthesis, 2011, 1599-1603.

2-Imidazolines were easily prepared in good yields from the reaction of aldehydes and ethylenediamine with iodine in the presence of potassium carbonate. The 2-imidazolines were smoothly oxidized to the corresponding imidazoles in good yields using (diacetoxyiodo)benzene at room temperature.
M. Ishihara, H. Togo, Synlett, 2006, 227-230.

Various 2-oxazolines were prepared from aromatic aldehydes and 2-aminoethanol with pyridinium hydrobromide perbromide in water at room temperature. The reaction of aromatic aldehydes with ethylenediamine gave 2-imidazolines in good yields under the same reaction conditions.
S. Sayama, Synlett, 2006, 1479-1484.

A one-pot, three-component cascade reaction combining photoredox catalyzed radical addition and formal [3 + 2] annulation provides imidazoline and oxazolidine derivatives in very good yields. The advantages of this transformation are mild reaction conditions, operational simplicity, and easy accessibility of raw materials.
J.-Q. Chen, W.-L. Yu, Y.-L. Wei, T.-H. Li, P.-F. Xu, J. Org. Chem., 2017, 82, 243-249.

The use of Cu(OAc)2 as the catalyst in the presence of PhI(OAc)2 and K3PO4 enables an amination of aliphatic C-H bonds of N-alkylamidines to yield dihydroimidazoles and tetrahydropyrimidines. A subsequent hydride reduction gives the corresponding diamines.
H. Chen, S. Synjaya, Y.-F. Wang, S. Chiba, Org. Lett., 2013, 15, 212-215.

A novel cationic Br initiated one-pot synthesis using olefin, nitrile, amine, and N-bromosuccinimide gives imidazolines in good yields. The olefinic substrates and the nitrile partners can be flexibly varied to achieve a range of imidazoline derivatives.
L. Zhou, J. Zhou, C. K. Tan, J. Chen, Y.-Y. Yeung, Org. Lett., 2011, 13, 2448-2451.

A mild reaction of α,α-difluoroalkyl amines with β-amino alcohols, β-amino thiols, and β-diamines affords the corresponding oxazoline, thiazoline, and imidazoline derivatives, respectively. The conditions are applicable for the synthesis of optically active heterocyclic compounds.
T. Fukuhara, C. Hasegawa, S. Hara, Synthesis, 2007, 1528-1534.

A palladium-catalyzed cyclization of 2,3-allenyl amines with aryl iodides provides polysubstituted 2-imidazoline derivatives in good yields via formation of new carbon-carbon and carbon-nitrogen bonds in a single synthetic operation.
Y. Liu, C. Zhang, X. Liang, X. Zeng, R. Lu, Z. Fang, S. Wang, Y. Liu, J. Hu, Synthesis, 2020, 52, 901-908.

A novel electrophilic one-pot reaction of an olefin, a cyanimide, an amine, and N-bromosuccinimide enables the synthesis of a number of guanidine derivatives with very good yields - including an rTRTVI precursor.
L. Zhou, J. Chen, J. Zhou, Y.-Y. Yeung, Org. Lett., 2011, 13, 5804-5807.

The key step in a new route for the construction of 2-aminoimidazolidines is an intramolecular microwave-assisted Staudinger/aza-Wittig cyclization of an in situ generated urea intermediate upon treatment with Bu3P or polymer-supported phosphine reagent. Furthermore, a useful one-pot Staudinger/aza-Wittig/Buchwald-Hartwig protocol leading to bicyclic guanidines has been elaborated.
R. Kumar, D. S. Ermolat'ev, E. V. Van der Eycken, J. Org. Chem., 2013, 78, 5737-5743.

Reaction of iodoethanol with aniline provides N-(2-iodoethyl)arylamine salts that are then converted to the corresponding iodide. A subsequent reaction with aliphatic or aromatic amines followed by triethyl orthoformate gave 26 different NHC ligands.
B. A. B. Prasad, S. R. Gilbertson, Org. Lett., 2009, 11, 3710-3713.

The reaction of formamidines and (2-bromoethyl)diphenylsulfonium triflate enables the synthesis of various symmetrical and unsymmetrical imidazolinium triflate salts in high yield in short reaction times under mild conditions. Aromatic and aliphatic N-substituents work well. The reaction is proposed to proceed via generation of a vinyl sulfonium salt intermediate from the bromoethylsulfonium triflate.
E. M. McGarrigle, S. P. Fritz, L. Favereau, M. Yar, V. K. Aggarwal, Org. Lett., 2011, 13, 3060-3063.

A very simple and efficient, microwave-assisted procedure is reported for the synthesis of 1,3-diarylimidazolinium chlorides by cyclization of N,N′-diarylethylenediamines dihydrochlorides with triethyl orthoformate.
A. Aidouni, A. Demonceau, L. Delaude, Synlett, 2006, 493-495.