Nitrone Cycloadditions to 1,2-Diphenylcyclopropenes and Subsequent Transformations of the Isoxazolidine Cycloadducts Vyacheslav V. Diev, ² Oksana N. Stetsenko, ² Tran Q. Tung, ² Ju ¨rgen Kopf, ‡ Rafael R. Kostikov, ² and Alexander P. Molchanov* ,² Department of Chemistry, St. Petersburg State UniVersity, 198504 UniVersitetsky pr. 26, St. Petersburg, Russian Federation, and Institut fu ¨r Anorganische Chemie, UniVersita ¨t Hamburg, Martin-Luter-King Platz 6, D-20146 Hamburg, Germany s.lab@pobox.spbu.ru ReceiVed NoVember 2, 2007 1,3-Dipolar cycloaddition of C-aryl,N-aryl (or N-methyl) nitrones with a number of 1,2-diphenylcyclopropenes sub- stituted at the C 3 position occurs with the formation of expected “normal” cycloadducts (with N-methylnitrones) and products of their subsequent transformations. Among them are corresponding R-acetophenyl aziridines and tetra (or penta) -arylpyrroles. Aziridines and the normal cycloadducts can be also thermally converted to such arylpyrroles with moderate to good yields. Substitution at the C 3 position of cyclopropenes by an electron acceptor group decreases the reactivity of cyclopropenes. The release of strain upon any type of addition or cycload- dition onto alkenes with three-membered carbon units such as cyclopropenes, 1 methylenecyclopropanes, 2 and bicyclopropy- lidenes 3 results in enhanced reactivity. This makes such alkenes especially attractive for synthetic applications. 1a-c,2,3 Among such strained compounds, cyclopropenes possess the most highly strained double C,C bond. 1 We demonstrated earlier the significance of electronic factors in determining the reactivity of cyclopropenes in the cycloaddition reaction with carbonyl ylides. 4 Corresponding cycloadducts with carbonyl ylides were formed in yields of up to 92% with cyclopropenes, but no reaction was observed or the yields of adducts were less than 5% in the case of 3-acceptor-substituted cyclopropenes. Frontier molecular orbital (FMO) analysis and the global electrophilicity index ω have been used to clarify the relative reactivity patterns. 4 We decided to examine whether these results are restricted to reactions with carbonyl ylides only. Among other 1,3-dipoles, nitrones have similar FMO characteristics and electrophilicity to the carbonyl ylides studied earlier. 5 Whereas 1,3-dipolar cycloadditions of nitrones with methylenecyclopropanes and bicyclopropylidenes have been investigated in great detail, 2,3a there is only a single report of cycloaddition of an electron- deficient nitrone with 3,3-dimethylcyclopropene. 6 In this paper, we wish to report the first systematic study of 1,3-dipolar cycloaddition of nitrones with cyclopropenes. 1,2-Diphenylcyclopropenes monosubstituted at the C 3 position (1a-e) were selected for investigation (Scheme 1). This enabled us to vary electronic properties of the substituent at the C 3 position. We performed 1,3-dipolar cycloaddition reactions with C-aryl-N-phenylnitrones 2a-d and C-phenyl-N-methylnitrone 2e (Scheme 1). In general, the reactions studied here differ in both reaction conditions and products formed. The results can be arranged into three distinct groups. I. Reactions of C-phenyl-N-methylnitrone 2e and cyclopro- penes 1a,b (benzene, reflux, 10-15 h) afforded expected “normal” cycloadducts 3a and 3b in yields of about 30% (Table 1, entries 5 and 8). Preferably the endo isomer of cycloadduct ² St. Petersburg State University. ‡ Universita ¨t Hamburg. (1) Reviews: (a) Rubin, M.; Rubina, M.; Gevorgyan, V. Chem. ReV. 2007, 107, 3117. (b) Rubin, M.; Rubina, M.; Gevorgyan, V. Synthesis 2006, 1221. (c) Methods of Organic Chemistry (Houben-Weyl); de Meijere, A., Ed.; Thieme: Stuttgart, Germany, 1997; Vol. E17a-d. (d) Baird, M. S. Chem. ReV. 2003, 103, 1271. (e) Dolbier, W. R., Jr.; Battiste, M. A. Chem. ReV. 2003, 103, 1071. (f) Binger, P.; Bu ¨ch, H. M. Top. Curr. Chem. 1987, 135, 77. (g) Deem, M. L. Synthesis 1972, 675. (h) Deem, M. L. Synthesis 1982, 701. (2) Reviews: (a) Brandi, A.; Cicchi, S.; Cordero, F. M.; Goti, A. Chem. ReV. 2003, 103, 1213. (b) Brandi, A.; Goti, A. Chem. ReV. 1998, 98, 589. (c) Goti, A.; Cordero, F. M.; Brandi, A. Top. Curr. Chem. 1996, 178, 1. (3) Reviews: (a) de Meijere, A.; Kozhushkov, S. I.; Khlebnikov, A. F. Top. Curr. Chem. 2000, 207, 89. (b) de Meijere, A.; Kozhushkov, S. I.; Khlebnikov, A. F. Zh. Org. Khim. 1996, 32, 1607; Russ. J. Org. Chem. (Engl. Transl.) 1996, 32, 1555. (4) (a) Diev, V. V.; Kostikov, R. R.; Gleiter, R.; Molchanov, A. P. J. Org. Chem. 2006, 71, 4066. (b) Molchanov, A. P.; Diev, V. V.; Kopf, J.; Kostikov, R. R. Russ. J. Org. Chem (Engl. Transl.) 2004, 40, 431. (5) For reviews on the 1,3-dipolar cycloaddition of nitrones, see: (a) Jones, R. C. F.; Martin, J. N. In Synthetic Application of 1,3-Dipolar Cycloaddition Chemistry Toward Heterocycles and Natural Products; Padwa, A., Pearson, W. H., Eds.; Wiley: New York, 2002; pp 1-81. (b) Torsell, K. B. G. Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis; VCH: Weinheim, Germany, 1988. (c) Tufariello, J. J. In 1,3- Dipolar Cycloaddition Chemistry; Padwa, A., Ed.; Wiley: New York, 1984; Vol. 2, pp 83-168. (6) Akmanova, N. A.; Sagitdinova, K. F.; Balenkova, E. S. Khim. Geterotsikl. Soedin. 1982, 1192; Chemistry of Heterocyclic Compounds (Engl. Transl.) 1982, 18, 910. In the reaction of C,N-diphenylnitrone with 1,3,3-trimethylcyclopropene, products were not identified: see ref 1h. (7) The unfavorable steric interactions between the proton at the C 3 position of the cyclopropene ring and substituent R1 of nitrones can occur in exo transitional state (exo-TS): 2396 J. Org. Chem. 2008, 73, 2396-2399 10.1021/jo702379d CCC: $40.75 © 2008 American Chemical Society Published on Web 02/28/2008