writing a summary for the research paper

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I have research paper of organic chemistry. I need to do summarization for this paper that includes everything in the paper of graph, chemical structures, and equations. The summary should be clear and connected information.

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ORGANIC LETTERS Gold Catalysis in Organic Synthesis: Efficient Cycloisomerization of r-Aminoallenes to 3-Pyrrolines 2004 Vol. 6, No. 22 4121-4123 Nobuyoshi Morita and Norbert Krause* Organic Chemistry II, Dortmund UniVersity, D-44221 Dortmund, Germany norbert.krause@uni-dortmund.de Received September 8, 2004 ABSTRACT The gold(III) chloride-catalyzed cycloisomerization of various r-aminoallenes gave the corresponding 3-pyrrolines in good to high chemical yields. An interesting dependence of the chirality transfer and reactivity on the N-protecting group was observed. The 3-pyrrolines are highly useful intermediates for the synthesis of functionalized pyrrolines, pyrrolidines, and other natural products. Functionalized pyrrolines and pyrrolidines are of great importance in natural product synthesis because of their high and diverse biological activities (Figure 1).1 These include Figure 1. Naturally occurring pyrrolidines. antifungal compounds (e.g., preussin, anisomycin2), hypotensive activity (codonopsinine3), anti-HIV activity, as well as various enzyme inhibitors such as lentiginosine, swainsonine, and alexine.1 (1) (a) O’Hagen, D. Nat. Prod. Rep. 2000, 17, 435. (b) Mauger, A. B. J. Nat. Prod. 1996, 59, 1205. (c) Huwe, C. M.; Blechert, S. Tetrahedron Lett. 1995, 36, 1621. (d) Anderson, W. K.; Milowsky, A. S. J. Med. Chem. 1987, 30, 2144. 10.1021/ol0481838 CCC: $27.50 Published on Web 10/08/2004 © 2004 American Chemical Society Thus, it is not surprising that numerous pathways for the synthesis of substituted pyrrolines and pyrrolidines have been developed, and in recent years much work has focused on metal-mediated approaches. To control the relative and absolute configuration of stereogenic centers in position 2 and/or 5 of the heterocycles, the cyclization/cyloisomerization of sterically defined R-aminoallenes is particularly promising, and metals such as Pd(0 or II),4 Ag(I),5 and Hg(II)6 as well as organolanthanides7 have been used for this purpose. (2) (a) Schwartz, R. E.; Liesch, J. Hensens, O.; Zitano, L.; Honeycutt, S.; Garrity, G.; Fromtling, R. A.; Onishi, J.; Monaghan, R. J. Antibiot. 1988, 41, 1774. (b) Johnson, J. H.; Phillipson, D. W.; Kahle, A. D. J. Antibiot. 1989, 42, 1184. (c) Hulme, A. N.; Rosser, E. M. Org. Lett. 2002, 4, 265. (d) Overhand, M.; Hecht, S. M. J. Org. Chem. 1994, 59, 4721. (e) Deng, W.; Overman, L. E. J. Am. Chem. Soc. 1994, 116, 11241. (f) McGrane, P. L.; Livinghouse, T. J. Am. Chem. Soc. 1993, 115, 11485. (g) Pak, C. S.; Lee, G. H. J. Org. Chem. 1991, 56, 1128. (3) (a) Matkhalikova, S. F.; Malikov, V. M.; Yunusov, S. Y. Khim. Prir. Soedin 1969, 5, 607. (b) Matkhalikova, S. F.; Malikov, V. M.; Yunusov, S. Y. Khim. Prir. Soedin 1969, 5, 30. (c) Severino, E. A.; Correia, C. R. D. Org. Lett. 2000, 2, 3039. (d) Yoda, H.; Nakajima, T.; Takabe, K. Tetrahedron Lett. 1996, 37, 5531. (e) Wang, C.-H. J.; Calabrese, J. C. J. Org. Chem. 1991, 56, 4341. (f) Iida, H.; Yamazaki, N.; Kibayashi, C. J. Org. Chem. 1987, 52, 1956. (4) (a) Ma, S.; Yu, F.; Gao, W. J. Org. Chem. 2003, 68, 5943. (b) Dieter, R. K.; Yu, H. Org. Lett. 2001, 3, 3855. (c) Kang, S.-K.; Kim, K.-J. Org. Lett. 2001, 3, 511. (d) Karstens, W. F. J.; Klomp, D.; Rutjes, F. P. J. T.; Hiemstra, H. Tetrahedron 2001, 57, 5123. (e) Ohno, H.; Toda, A.; Miwa, Y.; Taga, T.; Osawa, E.; Yamaoka, Y.; Fijii, N.; Ibuka, T. J. Org. Chem. 1999, 64, 2992. (f) Karstens, W. F. J.; Rutjes, F. P. J. T.; Hiemstra, H. Tetrahedron Lett. 1997, 35, 6257. (g) Davis, I. W.; Scopes, D. I.; Gallagher. Synlett 1993, 85. (h) Kimura, M.; Fugami, K.; Tanaka, S.; Tamaru, Y. J. Org. Chem. 1992, 57, 6377. (i) Prasad, J. S.; Liebeskind, L. S. Tetrahedron Lett. 1988, 29, 4257. Recently, we reported a highly efficient gold(III)catalyzed8 cycloisomerization of R-hydroxyallenes that provides 2,5-dihydrofurans with complete axis to center chirality transfer.9 This method is compatible with various functional groups present in the substrate and therefore highly suitable for application in natural product chemistry.10 We anticipated that a similar reaction with an R-aminoallene would bring about an efficient cycloisomerization to afford a 3-pyrroline, the double bond of which can then be utilized for further transformations, e.g., reductions, oxidations, etc. (Scheme 1). Scheme 2 Scheme 1 The synthesis of the starting materials, the diastereomerically pure aminoallenes 4a-e, is shown in Scheme 2. Epoxidation of enyne 1, followed by benzylation gave a 70% yield of oxirane 2. The corresponding hydroxyallene 3 was prepared via anti-selective SN2′ substitution reaction of oxirane 2 with a magnesium cyanocuprate in the presence of n-Bu3P.9,10 The R-aminoallene 4a was prepared from 3 via Mitsunobu reaction with phthalimide, followed by hydrazinolysis.11 For an initial screening of the effect of various N-protecting groups in the gold-catalyzed cyclization, aminoallene 4a was reacted with a selection of acylating and sulfonylating agents. Treatment of the diastereomerically pure R-aminoallenes 4a-e with 2 mol % of AuCl3 in dry CH2Cl2 at room temperature gave the corresponding 3-pyrrolines 5a-e in good to excellent yields (Table 1). The reactions were complete after 30 min at room temperature for the N-protected aminoallenes 4b-e (entries 2-7), whereas the unprotected substrate required a much longer reaction time (entry 1). A slight erosion of the stereoselectivity was observed in the cycloisomerization of the sulfonylated substrates 4b and 4c which was not affected (5) (a) Amombo, M. O.; Hausherr, A.; Reissig, H.-U. Synlett 1999, 1871. (b) Davis, I, W.; Gallagher, T.; Lamont, R. B.; Scopes, I. C. J. Chem. Soc. Chem. Commun. 1992, 335. (c) Kinsman, R.; Lathbury, D.; Vernon, P.; Gallagher, T. J. Chem. Soc., Chem. Commun. 1987, 243. (6) (a) Fox, D. N. A.; Lathbury, D.; Mahon, M. F.; Molly, K. C.; Gallagher, T. J. Chem. Soc., Chem. Commun. 1989, 1073. (7) Arrendondo, V. M.; Mcdonald, F. E.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 4871. (8) Recent reviews on gold catalysis in organic synthesis: (a) Hashmi, A. S. K. Gold Bull. 2004, 37, 51. (b) Arcadi, A.; Di Giuseppe, S. Curr. Org. Chem. 2004, 8, 795. (9) Hoffmann-Röder, A.; Krause, N. Org. Lett. 2001, 3, 2537. (10) Krause, N.; Hoffmann-Röder, A.; Canisius, J. Synthesis 2002, 1759. (11) Roush, W. R.; Straud, J. A.; Brown, R. T. J. Org. Chem. 1987, 52, 5127. 4122 by the solvent or temperature (entries 2-5). This effect was even more pronounced for the acylated aminoallenes 4d and 4e (entries 6 and 7). Only the unprotected aminoallene 4a afforded the diastereomerically pure 3-pyrroline (entry 1). Table 1. AuCl3-Catalyzed Cycloisomerization of R-Aminoallenes 4 to 3-Pyrrolines 5 entry 4 PG solvent T (°C) 1 2 3 4 5 6 7 4a 4b 4c 4c 4c 4d 4e H Ms Ts Ts Ts Ac Boc CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 THF CH2Cl2 CH2Cl2 rt rt rt 0 rt rt rt time 5 (yield, %) dr 5 days 30 min 30 min 1h 1.5 h 30 min 30 min 5a (74) 5b (77) 5c (93) 5c (95) 5c (95) 5d (80) 5e (69) >99:1 94:6 95:5 96:4 93:7 70:30 46:54 To further examine the scope of the gold-catalyzed cycloisomerization of R-aminoallenes, we prepared the substrates 6a-c with a variable substituent pattern. These were efficiently converted into the corresponding 3-pyrrolines 7a-c in good yields with complete chirality transfer (Table 2). A plausible mechanism of the gold(III) chloride-catalyzed cycloisomerization of R-aminoallenes is shown in Scheme 3. Thus, coordination of the carbophilic gold catalyst to an allenic double bond (complex A) would be followed by formation of the metallacyclopropane B. As a consequence of the increased electrophilicity, cyclization via an SN2-type transition state and subsequent proton transfer would produce the 3-pyrroline with complete axis-to-center chirality transfer. Org. Lett., Vol. 6, No. 22, 2004 Table 2. AuCl3-Catalyzed Cycloisomerization of R-Aminoallenes 6 to 3-Pyrrolines 7 entry 6 R R′ dr 7 (yield, %) dr 1 2 3 6a 6b 6c Me n-hexyl Ph Bn TBS TBS 90:10 85:15 >99:1 7a (71) 7b (82) 7c (79) 90:10 85:15 >99:1 In the case of the N-protected aminoallenes 4b-e, however, an oxygen atom of the protecting group could stabilize the zwitterionic complex C by coordination, and the cyclization Scheme 3 would proceed with partial isomerization (via single bond rotation) to complex D, leading to a diminished diastereoselectivity. In conclusion, we have developed a new efficient gold(III)-catalyzed cycloisomerization reaction of various R-aminoallenes to the corresponding 3-pyrrolines. An interesting dependence of the chirality transfer and reactivity on the N-protecting group was observed. Compared to the corresponding Ag(I)-catalyzed cyclization of aminoallenes,5 our catalytic system is advantageous in terms of a very low catalyst loading (2 mol %), which renders the method much more economical. We are now searching for more active and selective gold catalysts, which should allow for shorter reaction times in case of the unprotected R-aminoallenes, and for higher stereoselectivities in case of the N-protected substrates. Furthermore, application of the method to the synthesis of functionalized pyrrolines, pyrrolidines, and other natural products is actively pursued. Acknowledgment. Continuous support of our work by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. Supporting Information Available: Experimental procedure and 1H and 13C NMR data of 3-pyrrolines. This material is available free of charge via the Internet at http://pubs.acs.org. OL0481838 Org. Lett., Vol. 6, No. 22, 2004 4123

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