Unprecedented Highly cis-Diastereoselective Olefin Cyclopropanation Using Copper Homoscorpionate Catalysts M. Mar Dı ´az-Requejo, † Toma ´s R. Belderraı ´n, † Swiatoslaw Trofimenko, ‡ and Pedro J. Pe ´rez* ,† Departamento de Quı ´mica y Ciencia de Materiales UniVersidad de HuelVa Carretera de Palos de la Frontera s/n 21819-HuelVa, Spain Department of Chemistry and Biochemistry UniVersity of Delaware, Newark, Delaware 19716 ReceiVed January 23, 2001 Among the metal-based catalysts examined for the intermo- lecular olefin cyclopropanation reaction, those of rhodium and copper have been preferentially employed in the past decade. 1,2 Rhodium catalysts are usually derived from Rh 2 (OAc) 4 , and complexes containing chiral ligands such as carboxylates or carboxamidates have induced high enantioselection in this transformation. 3 Porphyrin-rhodium complexes have also shown remarkable catalytic activity and asymmetric induction. 1,3 Copper- (I) complexes with chiral salicylaldimines, bis(oxazolines), semi- corrines, and bipyridines have shown similar effect, and high ee’s have been reported. 1-3 In contrast to these results, there is still one elusive goal: the diastereocontrol of the reaction. The influence of the structure (catalyst, olefin) in diastereoselectivity is not high, a fact that has been rationalized by assuming that the high reactivity of the metal-carbene complex results in an early transition state (A) in which the olefin is still a significant distance from the metal center. Because of this, steric influences are not important in the induction of diastereomeric excesses (de), unless very bulky reactants (diazoacetate and olefin) are employed. The cyclopropanation of styrene with ethyl diazoacetate (EDA) has been studied as a model for this reaction (eq 1). Most catalysts lead to cis:trans ratios in the range 50:50 to 25:75. 1-3 Only a few examples are known that have provided high trans diaste- reoselectivities. The catalyst RuCl 2 (pybox) gave 4 a 9:91 cis:trans ratio, and the porphyrin osmium Os(TPP) (TPP ) tetraphenylpor- phyrin) moved that ratio to 1:13 (cis:trans). 5 On the other hand, few catalysts favor the formation of the cis isomer, 1 the maximum diastereoselectivity corresponding to Hossain’s iron-based catalyst, [Cp(CO) 2 Fe(THF)] + , 6 (84:16 cis:trans ratio, 40% yield). The use of copper-catalysts have not provided better results: the highest cis selectivity has been reported by Brunner and co-workers using a chiral, camphor-derived tetrakispyrazolylborate copper (I) complex, (74:26, cis:trans). 7 The situation with other olefins is quite similar, and only high trans diastereoselectivities have been induced by means of very bulky diazoacetates. The menthyl or the BHT derivatives have provided a noticeable amount of the trans isomer of the corresponding cyclopropanes for 1-alkenes. 8 More interesting is the cyclopropanation of 2,5-dimethyl-2,4- hexadiene to give the chrysanthemate ester (eq 2), due to its use in pesticide industry. Previous reports on this reaction gave preferentially trans diastereoselectivity when the aforementioned bulky diazoacetates where employed. Masamune 9 reported 16: 84 cis:trans formation with a copper-based catalyst and menthyl diazoacetate. Doyle later provided a 6:94 cis:trans ratio when using rhodium acetate and BDA as the carbene source. To our knowledge, a catalyst that generates a diastereomeric excess on the cis isomer with EDA as the carbene source and 1-alkenes or 2,5-dimethyl-2,4-hexadiene is yet unknown. We have recently reported 10 the use of bispyrazolylborate- copper complexes as catalysts for the olefin cyclopropanation reaction. An earlier report showed 11 that the complex Tp*Cu (1; Tp* ) hydrotris(3,5-dimethylpyrazolyl)borate) catalyzed the conversion of olefins into the corresponding cyclopropanes, with a 55:45 cis:trans selectivity. In this contribution we present the results of the olefin cyclopropanation reaction with a series of in situ generated copper(I) complexes of general formula Tp X Cu, in which the groups attached to the pyrazolyl rings have been varied to probe steric effects on the catalytic reaction. The catalyst precursors were prepared in situ upon reacting CuI with the thalium (or potassium) salt of the corresponding * Author correspondence. E-mail: perez@dqcm.uhu.es. † Universidad de Huelva. ‡ University of Delaware. (1) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic Methods for Organic Synthesis with Diazo Compounds; John Wiley & Sons: New York 1998. (2) Doyle, M. P. In ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, U. K., 1995; Vol. 12, p 387. (3) (a) Doyle, M. P.; Protopopova, M. N. Tetrahedron 1998, 54, 7919. (b) Pfaltz, A., Yamamoto, H., Jacobsen, E. N., Eds.; ComprehensiVe Asymmetric Catalysis; Springer-Verlag 1999; Chapter 16. (4) Nishiyama, H.; Itoh, Y.; Matsumoto, H.; Park, S.-B.; Itoh, K. J. Am. Chem. Soc. 1994, 116, 2223 (5) Smith, D. A.; Reynolds, D. N.; Woo, L. K. J. Am. Chem. Soc. 1993, 115, 2511 (6) Seit, W. J.; Saha, A. K.; Hossain, M. M. Organometallics 1993, 12, 2604. (7) Brunner, H.; Singh, U. P.; Boeck, T.; Altmann, S.; Scheck, T.; Wrackmeyer, B. J. Organomet. Chem. 1993, 443, C16-C18. (8) (a) Doyle, M. P.; Bagheri, V.; Wandless, T. J.; Harn, N. K.; Brinker, D. A.; Eagle, C. T.; Loh, K.-L. J. Am. Chem. Soc. 1990, 112, 1906. (b) Lowenthal, R. E.; Abiko, A.; Masamune, S. Tetrahedron Lett. 1990, 31, 6008. (c) Aratani, T. Pure Appl. Chem. 1985, 57, 1839. (9) Lowenthal, R. E.; Masamune, S. Tetrahedron Lett. 1991, 32, 7373. (10) Dı ´az-Requejo, M. M.; Nicasio, M. C.; Pe ´rez, P. J. Organometallics 1998, 17, 3051. (11) (a) Pe ´rez, P. J.; Brookhart, M.; Templeton, J. L. Organometallics 1993, 12, 261. (b) Diaz-Requejo, M. M.; Pe ´rez, P. J.; Brookhart, M.; Templeton, J. L. Organometallics 1997, 16, 4399. 3167 J. Am. Chem. Soc. 2001, 123, 3167-3168 10.1021/ja0155736 CCC: $20.00 © 2001 American Chemical Society Published on Web 03/09/2001