Propargylic ureas as powerful and versatile building blocks in the synthesis of various key medicinal heterocyclic compounds

Document Type: Review Article

Authors

1 Bowling Green State University

2 Qatar University

3 Islamic Azad University

4 Payame Noor University

Abstract

This review article is an attempt to highlight the most important contributions toward the synthesis of various nitrogen-containing heterocyclic compounds from corresponding propargylic ureas through regio- and chemoselective 5-exo-dig and 6-endo-dig modes of N- and O-cyclization reactions. The review is divided into three major sections. In the first section we only focus on 5-exo-dig N-cyclization fashion. In the second section 5-exo-dig O-cyclization is described. The third section is devoted to 6-endo-dig N- and O-cyclizations

Graphical Abstract

Propargylic ureas as powerful and versatile building blocks in the synthesis of various key medicinal heterocyclic compounds

Keywords


[1] a) S. Shahidi, P. Farajzadeh, P. Ojaghloo, A. Karbakhshzadeh, A. Hosseinian, Nanocatalysts for conversion of aldehydes/alcohols/amines to nitriles: A review, Chem. Rev. Lett. 1 (2018) 37-44; b) S. Mohammadi, M. Musavi, F. Abdollahzadeh, S. Babadoust, A. Hosseinian, Application of Nanocatalysts in C-Te Cross-Coupling Reactions:  An Overview,Chem. Rev. Lett. 1 (2018) 49-55; c) T. L. Gilchrist, Heterocyclic Chemistry, 3rd ed. Addison Wesley: Essex, England, 1997. 414 pp. ISBN 0-582-27843-0.

[2] a)  E. Vessally, M. Abdoli., Oxime ethers as useful synthons in the synthesis of a number of key medicinal heteroaromatic compounds. J. Iran. Chem. Soc.,13 (2016) 1235-1256; b) V. Bhardwaj, D. Gumber, V. Abbot, S. Dhiman, P. Sharma. Pyrrole: a resourceful small molecule in key medicinal hetero-aromatics. RSC Adv., 5 (2015) 15233-15266; c) A. Marella, O.P. Tanwar, R. Saha, M. R. Ali, S. Srivastava, M. Akhter, M. Shaquiquzzaman, M. M. Alam. Quinoline: A versatile heterocyclic. Saudi. Pharm. J., 21 (2013) 1-12; d) M. Baumann, I. R. Baxendale. An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles. Beilstein J. Org. Chem., 9 (2013) 2265-2319; e) S. B. Ferreira, C. R. Kaiser. Pyrazine derivatives: a patent review (2008–present). Expert Opin. Ther. Pat., 22 (2012) 1033-1051; f) N.K. Kaushik, N. Kaushik, P. Attri, N. Kumar, C.H. Kim, A.K. Verma, E.H. Choi. Biomedical importance of indoles. Molecules., 18 (2013) 6620-6662; g) S. Y. Essack. The development of β-lactam antibiotics in response to the evolution of β-lactamases, Pharm. Res., 18 (2001) 1391-1399.

[3] R. Dua, S. Shrivastava, S. Sonwane, S. Srivastava, Pharmacological significance of synthetic heterocycles scaffold: a review. Adv. Biol. Res., 5 (2011) 120-144.

[4] P. Martins, J. Jesus, S. Santos, L. R. Raposo, C. Roma-Rodrigues, P. V. Baptista, A.R. Fernandes. Heterocyclic anticancer compounds: recent advances and the paradigm shift towards the use of nanomedicine's tool box. Molecules., 20 (2015) 16852-16891.

[5] a) G. Zeni, R. C. Larock. Synthesis of heterocycles via palladium π-olefin and π-alkyne chemistry. Chem. Rev., 104 (2004) 2285-2310; b) N. T. Patil, Y. Yamamoto. Chem. Rev., 108 (2008) 3395-3442; c) X. -F. Wu, H. Neumann, M. Beller. Synthesis of heterocycles via palladium-catalyzed carbonylations. Chem. Rev., 113 (2012) 1-35; d) B. Stanovnik, J. Svete. Synthesis of heterocycles from alkyl 3-(dimethylamino) propenoates and related enaminones. Chem. Rev., 104 (2004) 2433-2480; e) G. Balme, E. Bossharth, N. Monteiro. Pd‐assisted multicomponent synthesis of heterocycles. Eur. J. Org. Chem., (2003) 4101-4111.

[6] a) B. Godoi, R. F. Schumacher, G. Zeni. Synthesis of heterocycles via electrophilic cyclization of alkynes containing heteroatom. Chem. Rev., 111 (2011) 2937-2980; b) S. A. Vizer, E. S. Sycheva, A. A. A. Al Quntar, N. B. Kurmankulov, K. B. Yerzhanov, V. M. Dembitsky. Chem. Rev., 115 (2014) 1475-1502; c) Y. Hu, X. Xin, B. Wan. Cyclization reactions of propargylic amides: mild access to N-heterocycles. Tetrahedron Lett., 56 (2015) 32-52.

[7] S. Sarhandi, M. Daghagheleh, M. Vali, R. Moghadami, E. Vessally, New insight in Hiyama cross-coupling reactions: Decarboxylative, denitrogenative and desulfidative couplings: A review, Chem. Rev. Lett. 1 (2018) 9-15.

[8] M. Daghagheleh, M. Vali, Z. Rahmani, S. Sarhandi, E. Vessally, A review on the CO2 Incorporation Reactions Using Arynes, Chem. Rev. Lett. 1 (2018) 23-30.

[9] a) E. Vessally, A new avenue to the synthesis of highly substituted pyrroles: synthesis from N-propargylamines, RSC Adv., 6 (2016) 18619-18631; b) E. Vessally, H. Saeidian, A. Hosseinian, L. Edjlali, A. Bekhradnia, A review on synthetic applications of oxime esters, Curr.Org. Chem., 21 (2017) 249-271; c) E. Vessally, L. Edjlali, A. Hosseinian, A. Bekhradnia, M.D. Esrafili, Novel routes to quinoline derivatives from N-propargylamines, RSC Adv., 6 (2016) 49730-49746; d) E. Vessally, A. Hosseinian, L. Edjlali, A. Bekhradnia, M.D. Esrafili, New page to access pyridine derivatives: synthesis from N-propargylamines, RSC Adv., 6 (2016) 71662-71675; e) E. Vessally, A. Hosseinian, L. Edjlali, A. Bekhradnia, M. D Esrafili, New page to access pyrazines and their ring fused analogues: Synthesis from N-propargylamines, Curr.Org. Synth., 14 (2017) 557-567; f) E. Vessally, A. Hosseinian, L. Edjlali, A. Bekhradnia, M.D. Esrafili, New route to 1, 4-oxazepane and 1, 4-diazepane derivatives: synthesis from N-propargylamines, RSC Adv., 6 (2016) 99781-99793; g) E. Vessally, S. Soleimani-Amiri, A. Hosseinian, L. Edjlali, A. Bekhradnia, New protocols to access imidazoles and their ring fused analogues: synthesis from N-propargylamines, RSC Adv., 7 (2017) 7079-7091; h) M. Babazadeh, S. Soleimani-Amiri, E. Vessally, A. Hosseinian, L. Edjlali, Transition metal-catalyzed [2+ 2+ 2] cycloaddition of nitrogen-linked 1, 6-diynes: a straightforward route to fused pyrrolidine systems, RSC Adv., 7 (2017) 43716-43736; i) S. Arshadi, E. Vessally, L. Edjlali, R. Hosseinzadeh-Khanmiri, E. Ghorbani-Kalhor, N-Propargylamines: versatile building blocks in the construction of thiazole cores, Beilstein J. Org. Chem., 13 (2017) 625-638; j) E. Vessally, A. Hosseinian, L. Edjlali, E. Ghorbani-Kalhor, R. Hosseinzadeh-Khanmiri, Intramolecular cyclization of N-propargyl anilines: a new synthetic entry into highly substituted indoles, J. Iran. Chem. Soc., 14 (2017) 2339-2353; k) S. Arshadi, E. Vessally, L. Edjlali, E. Ghorbani-Kalhor, R. Hosseinzadeh-Khanmiri, N-Propargylic β-enaminocarbonyls: powerful and versatile building blocks in organic synthesis, RSC Adv., 7 (2017) 13198-13211; l) E. Vessally, A. Hosseinian, L. Edjlali, M. Babazadeh, R. Hosseinzadeh-Khanmiri, New strategy for the synthesis of morpholine cores: synthesis from N-propargylamines, Iran. J. Chem. Chem. Eng., 36 (2017) 1-13; m) S. Arshadi, E. Vessally, M. Sobati, A. Hosseinian, A. Bekhradnia, Chemical fixation of CO2 to N-propargylamines: a straightforward route to 2-oxazolidinones, J. CO2 Util., 19 (2017) 120-129.

[10] S. Soleimani-Amiri, E. Vessally, M. Babazadeh, A. Hosseinian, L. Edjlali, Intramolecular cyclization of N-allyl propiolamides: a facile synthetic route to highly substituted γ-lactams (a review), RSC Adv., 7 (2017) 28407-28418; b) E. Vessally, M. Babazadeh, A. Hosseinian, L. Edjlali, L. Sreerama, Recent Advances in Synthesis of Functionalized β-Lactams through Cyclization of N-Propargyl Amine/Amide Derivatives, Curr. Org. Chem., 22 (2018) 199-205; c) E. Vessally, A. Hosseinian, M. Babazadeh, L. Edjlali, R. Hosseinzadeh-Khanmiri, Metal Catalyzed Carboxylative Coupling of Terminal Alkynes, Organohalides and Carbon Dioxide: A Novel and Promising Synthetic Strategy toward 2-Alkynoates (A Review), Curr. Org. Chem., 22 (2018) 315-322; d) E. Vessally, M. Nikpasand, S. Ahmadi, P.D.K. Nezhad, A. Hosseinian, Transition metal-catalyzed intramolecular cyclization of N-Boc-protected propargyl/ethynyl amines: a novel and convenient access to 2-oxazolidinone/oxazolone derivatives, J. Iran. Chem. Soc., (2018) DOI: 10.1007/s13738-018-1542-5; e) S. Arshadi, E. Vessally, A. Hosseinian, S. Soleimani-amiri, L. Edjlali, Three-component coupling of CO2, propargyl alcohols, and amines: An environmentally benign access to cyclic and acyclic carbamates (A Review), J. CO2 Util., 21 (2017) 108-118; f) E. Vessally, S. Soleimani-Amiri, A. Hosseinian, L. Edjlali, M. Babazadeh, Chemical fixation of CO2 to 2-aminobenzonitriles: a straightforward route to quinazoline-2, 4 (1H, 3H)-diones with green and sustainable chemistry perspectives, J. CO2 Util., 21 (2017) 342-352; g) E. Vessally, M. Babazadeh, A. Hosseinian, S. Arshadi, L. Edjlali, Nanocatalysts for chemical transformation of carbon dioxide, J. CO2 Util., 21 (2017) 491-502.

[11] a) A. Hosseinian, S. Farshbaf, L.Z. Fekri, M. Nikpassand, E. Vessally, Cross-Dehydrogenative Coupling Reactions Between P (O)–H and X–H (X= S, N, O, P) Bonds, Top. Curr. Chem., 376 (2018) 23; b) F.A.H. Nasab, L.Z. Fekri, A. Monfared, A. Hosseinian, E. Vessally, Recent advances in sulfur–nitrogen bond formation via cross-dehydrogenative coupling reactions, RSC Adv., 8 (2018) 18456-18469; c) S. Farshbaf, L.Z. Fekri, M. Nikpassand, R. Mohammadi, E. Vessally, Dehydrative condensation of β-aminoalcohols with CO 2: An environmentally benign access to 2-oxazolidinone derivatives, J. CO2 Util., 25 (2018) 194-204; d) A. Hosseinian, S. Ahmadi, A. Monfared, P.D. Nezhad, E. Vessally, Nano-structured Catalytic Systems in Cyanation of Aryl Halides with K4 [Fe (CN) 4], Curr. Org. Chem., 22 (2018) 1862-1874; e) A. Hosseinian, L. Zare Fekri, A. Monfared, E. Vessally, M. Nikpassand, Transition-metal-catalyzed C–N cross-coupling reactions of N-unsubstituted sulfoximines: a review, J. Sulfur Chem., 39 (2018) 674-698; f) K. Nejati, S. Ahmadi, M. Nikpassand, P.D.K. Nezhad, E. Vessally, Diaryl ethers synthesis: nano-catalysts in carbon-oxygen cross-coupling reactions, RSC Adv., 8 (2018) 19125-19143; g) A. Hosseinian, S. Ahmadi, F.A.H. Nasab, R. Mohammadi, E. Vessally, Cross-Dehydrogenative C–H/S–H Coupling Reactions, Top. Curr. Chem., 376 (2018) 39; h) A. Hosseinian, F.A.H. Nasab, S. Ahmadi, Z. Rahmani, E. Vessally, Decarboxylative cross-coupling reactions for P (O)–C bond formation, RSC Adv., 8 (2018) 26383-26398.

[12] a) K. Didehban, E. Vessally, A. Hosseinian, L. Edjlali, E.S. Khosroshahi, Nanocatalysts for C–Se cross-coupling reactions, RSC Adv., 8 (2018) 291-301; b) E. Vessally, R. Mohammadi, A. Hosseinian, K. Didehban, L. Edjlali, S-arylation of 2-mercaptobenzazoles: a comprehensive review, J. Sulfur Chem., 39 (2018) 443-463; c) A. Hosseinian, S. Farshbaf, R. Mohammadi, A. Monfared, E. Vessally, Advancements in six-membered cyclic carbonate (1, 3-dioxan-2-one) synthesis utilizing carbon dioxide as a C1 source, RSC Adv., 8 (2018) 17976-17988.

[13] a) A. Hosseinian, M. Babazadeh, L. Edjlali, Z. Rahmani, E. Vessally, Intramolecular Cyclization of Aryl Propargyl Ethers: A Straightforward and Convenient Approach to Benzofuran Derivatives, Curr. Org. Synth., 15 (2018) 972-981; b) K. Didehban, E. Vessally, M. Salary, L. Edjlali, M. Babazadeh, Synthesis of a variety of key medicinal heterocyclic compounds via chemical fixation of CO2 onto o-alkynylaniline derivatives, J. CO2 Util., 23 (2018) 42-50; c) E. Vessally, R. Mohammadi, A. Hosseinian, L. Edjlali, M. Babazadeh, Three component coupling of amines, alkyl halides and carbon dioxide: An environmentally benign access to carbamate esters (urethanes), J. CO2 Util., 24 (2018) 361-368; d) E. Vessally, K. Didehban, R. Mohammadi, A. Hosseinian, M. Babazadeh, Recent advantages in the metal (bulk and nano)-catalyzed S-arylation reactions of thiols with aryl halides in water: a perfect synergy for eco-compatible preparation of aromatic thioethers, J. Sulfur Chem., 39 (2018) 332-349.

[14] E. Vessally, R. Hosseinzadeh-Khanmiri, E. Ghorbani-Kalhor, M. Es' haghi, A. Bekhradnia, Domino carbometalation/coupling reactions of N-arylpropiolamides: a novel and promising synthetic strategy toward stereocontrolled preparation of highly substituted 3-methyleneindolinones, RSC Adv., 7 (2017) 19061-19072.

[15] E. Vessally, M. Babazadeh, K. Didehban, A. Hosseinian, L. Edjlali, Intramolecular ipso-Cyclization of N-Arylpropiolamides: A Novel and Straightforward Synthetic Approach for Azaspiro [4.5] decatrien-2-ones, Curr. Org. Chem., 22 (2018) 286-297.

[16] E. Vessally, M. Babazadeh, K. Didehban, A. Hosseinian, L. Edjlali, Intramolecular Cyclization of N-Arylpropiolamides: A New Strategy for the Synthesis of Functionalized 2-Quinolones, Curr. Org. Chem., 21 (2017) 2561-2572.

[17] E. Vessally, K. Didehban, M. Babazadeh, A. Hosseinian, L. Edjlali, Chemical fixation of CO2 with aniline derivatives: A new avenue to the synthesis of functionalized azole compounds (A review), J. CO2 Util., 21 (2017) 480-490.

[18] E. Vessally, A. Hosseinian, L. Edjlali, M. Babazadeh, K. Didehban, Chemical Fixation of CO2 to Allylic (α-Allenylic) Amines: A Green Route to Synthesis of Functionalized 2-Oxazolidones, Mini-Rev. Org. Chem., 15 (2018) 315-323.

[19] L. Zhang, X. M. Peng, G. L. Damu, R. X. Geng, C. H. Zhou. Comprehensive review in current developments of imidazole‐based medicinal chemistry. Med. Res. Rev., 34 (2014) 340-437.

[20] A. R. Carroll, S. Duffy, V. M. Avery. Citronamides A and B, Tetrapeptides from the australian sponge Citronia astra. J. Nat. Prod., 72 (2009) 764-768.

[21] S. C. Reddymasu, I. Soykan, R. W. McCallum. Domperidone: Review of pharmacology and clinical applications in gastroenterology. Am. J. Gastroenterol.. 102 (2007) 2036-2044.

[22] Palmer, W. S.; Poncet-Montange, G.; Liu, G.; Petrocchi, A.; Reyna, N.; Subramanian, G.; Theroff, J.; Yau, A.; Kost-Alimova, M.; Bardenhagen. J.P. Structure-guided design of IACS-9571, a selective high-affinity dual TRIM24-BRPF1 bromodomain inhibitor. J. Med. Chem., 59 (2015) 1440-1454.

[23] N. Shachat, J. J. Bagnell Jr. Reactions of propargyl alcohols and propargylamines with isocyanates. J. Org. Chem., 28 (1963) 991-995.

[24] a) C. Proulx, W. D. Lubell. N-amino-imidazolin-2-one peptide mimic synthesis and conformational analysis. Org. Lett., 14 (2012) 4552-4555; b) C. Proulx, W. D. Lubell. Analysis of N‐amino‐imidazolin‐2‐one peptide turn mimic 4‐position substituent effects on conformation by X‐ray crystallography. Biopolymers., 102 (2014) 7-15.

[25] V. A. Peshkov, O. P. Pereshivko, S. Sharma, T. Meganathan, V. S. Parmar, D. S. Ermolat’ev, E. V. Van der Eycken. Tetrasubstituted 2-imidazolones via Ag (I)-catalyzed cycloisomerization of propargylic ureas. J. Org. Chem., 76 (2011) 5867-5872.

[26] A. Ranjan, R. Yerande, P. B. Wakchaure, S.G. Yerande, D. H. Dethe. Base-mediated hydroamination of propargylamine: A regioselective intramolecular 5-exo-dig cycloisomerization en route to imidazole-2-thione. Org. Lett., 16 (2014) 5788-5791.

[27] F. Huguenot, C. Delalande, M. Vidal. Metal-free 5-exo-dig cyclization of propargyl urea using TBAF. Tetrahedron Lett., 55 (2014) 4632-4635.

[28] A. La-Venia, N. S. Medran, V. Krchňák, S. A. Testero. Synthesis of a small library of imidazolidin-2-ones using gold catalysis on solid phase. ACS. Comb. Sci., 18 (2016) 482-489.

[29] a) ) S. P. Gaine, L. J. Rubin, J. J. Kmetzo, H. I. Palevsky, T. A. Traill. Recreational use of aminorex and pulmonary hypertension. Chest., 118 (2000) 1496-1497; b) R. A. Glennon, B. Misenheimer. Stimulus properties of a new designer drug: 4-methylaminorex (“U4Euh”). Pharmacol. Biochem. Behav., 35 (1990) 517-521; c) S. Bansal, A. Halve. Oxazolines: Their synthesis and biological activity. Int. J. Pharm. Sci. Res., 5 (2014) 4601-4616.

[30] a) Z. M. Ištuk, A. Čikoš, D. Gembarovski, G. Lazarevski, I. Đilović, D. Matković-Čalogović, G. Kragol, G. Novel 9a, 11-bridged azalides: One-pot synthesis of N′-substituted 2-imino-1, 3-oxazolidines condensed to an azalide aglycone. Bioorg. Med. Chem., 19 (2011) 556-566; b) A. A. Nirschl, Y. Zou, S. R. Krystek Jr, J. C. Sutton, L. M. Simpkins, J. A. Lupisella, J. E. Kuhns, R. Seethala, R. Golla, P. G. Sleph, N-Aryl-oxazolidin-2-imine muscle selective androgen receptor modulators enhance potency through pharmacophore reorientation. J. Med. Chem., 52 (2009) 2794-2798; c) J. Castilla, R. Rísquez, D. Cruz, K. Higaki, E. Nanba, K. Ohno, Y. Suzuki, Y. Díaz, C. Ortiz Mellet, J. M. García Fernández, Conformationally-locked N-glycosides with selective β-glucosidase inhibitory activity: identification of a new non-iminosugar-type pharmacological chaperone for Gaucher disease. J. Med. Chem., 55 (2012) 6857-6865.

[31] S. Ueda, H. Terauchi, A. Yano, M. Ido, M. Matsumoto, M. Kawasaki, 4, 5-Disubstituted-1, 3-oxazolidin-2-imine derivatives: a new class of orally bioavailable nitric oxide synthase inhibitor. Bioorg. Med. Chem. Lett., 14(2004) 313-316.

[32] G. Wegener, V. Volke, Nitric oxide synthase inhibitors as antidepressants. Pharmaceuticals., 3 (2010) 273-299.

[33] a) C. Larksarp, H. Alper, Highly enantioselective synthesis of 1, 3-oxazolidin-2-imine derivatives by asymmetric cycloaddition reactions of vinyloxiranes with unsymmetrical carbodiimides catalyzed by palladium (0) complexes. J. Org. Chem., 63(1998) 6229-6233; b) T. Munegumi, I. Azumaya, T. Kato, H. Masu, S. Saito, [3+2] Cross-coupling reactions of aziridines with isocyanates catalyzed by nickel (II) iodide. Org. Lett., 8 (2006) 379-382; c) M. A. Tabarki, R. Besbes, Ring expansion of aziridine-2-carboxylates. An efficient entry to imidazolidin-2-ones and oxazolidin-2-imines. Tetrahedron Lett., 56(2015) 1837-1839.

[34] M. J. Campbell, F. D. Toste. Enantioselective synthesis of cyclic carbamimidates via a three-component reaction of imines, terminal alkynes, and p-toluenesulfonylisocyanate using a monophosphine gold(I) catalyst. Chem. Sci., 2 (2011) 1369-1378.

[35] T. Kusakabe, K. Kawaguchi, M. Kawamura, N. Niimura, R. Shen, H. Takayama, K. Kato. Cyclization-carbonylation-cyclization coupling reaction of propargyl ureas with palladium (II)-bisoxazoline catalyst. Molecules., 17 (2012) 9220-9230.

[36] S. Huang, Y. Shao, R. Liu, X. Zhou. Facile access to oxazolidin-2-imine, thiazolidin-2-imine and imidazolidin-2-imine derivatives bearing an exocyclic haloalkyliene via direct halocyclization between propargylamines, heterocumulenes and I2 (NBS). Tetrahedron., 71 (2015) 4219-4226.

[37] (a) C. O. Kappe, Biologically active dihydropyrimidones of the Biginelli-type—a literature survey. ‎Eur. J. Med. Chem. 2000, 35, 1043-1052; (b) Â. de Fátima, T. C. Braga, L. d. S. Neto, B. S. Terra, B. G. Oliveira, D. L. da Silva, L. V. Modolo, A mini-review on Biginelli adducts with notable pharmacological properties. J. Adv. Res., 6(2015) 363-373.

[38] K. Beena, R. Suresh, A. Rajasekaran, P. Manna, Dihydropyrimidinones-a versatile scaffold with diverse biological activity. J. Pharm. Sci. Res., 8(2016) 741-746.

[39] a) M. R. de Brito, W. J. Peláez, M. S. Faillace, G. C Militão, J. R. Almeida, G. A. Argüello, Z. Szakonyi, F. Fülöp, M. C. Salvadori, F. S. Teixeira, Cyclohexene-fused 1, 3-oxazines with selective antibacterial and antiparasitic action and low cytotoxic effects. Toxicol In Vitro., 44 (2017) 273-279; b) K. Fuchino, Y. Mitsuoka, M. Masui, N. Kurose, S. Yoshida, K. Komano, T. Yamamoto, M. Ogawa, C. Unemura, M. Hosono, Rational design of novel 1, 3-oxazine based β-secretase (BACE1) inhibitors: Incorporation of a double bond to reduce P-gp efflux leading to robust Aβ reduction in the brain. J. Med. Chem., 61 (2018) 5122-5137.

[40] M. Yang, S. J. Odelberg, Z. Tong, D. Y. Li, R. E. Looper. Cationic dirhodium carboxylate-catalyzed synthesis of dihydropyrimidones from propargyl ureas. Tetrahedron., 69 (2013) 5744-5750.

[41] O. P. Pereshivko, V. A. Peshkov, A. A. Peshkov, J. Jacobs, L. Van Meervelt, E. V. Van der Eycken. Unexpected regio-and chemoselectivity of cationic gold-catalyzed cycloisomerizations of propargylureas: access to tetrasubstituted 3, 4-dihydropyrimidin-2 (1 H)-ones. Org. Biomol. Chem., 12 (2014) 1741-1750.

[42] S. Gupta, D. Koley, K. Ravikumar, B. Kundu. Counter ion effect in Au/Ag-catalyzed chemoselective 6-endo-dig N- and O-cyclizations of enyne–urea system: Diversity-oriented synthesis of annulated indoles. J. Org. Chem., 78 (2013) 8624-8633