Solvent and Stereoelectronic Effects on the Solvolysis Rates of Oxaspirocyclopropanated 1-Norbornyl Triflates and Related Bridgehead Derivatives Antonio Garcı ´a Martı ´nez,* Santiago de la Moya Cerero,* Enrique Teso Vilar, † Amelia Garcı ´a Fraile, † Beatriz Lora Maroto, and Cristina Dı ´az Morillo Departamento de Quı ´mica Orga ´nica I, Facultad de Ciencias Quı ´micas, UniVersidad Complutense de Madrid, Ciudad UniVersitaria, 28040 Madrid, Spain agamar@quim.ucm.es ReceiVed May 6, 2008 The study of the stereochemical outcome of the solvolysis of oxaspirocyclopropanated 1-norbornyl triflates is highly interesting since these reactions do not lead to the usual retention or fragmentation products but only synthetically interesting rearranged products are enantiospecifically formed. There is no correlation between the experimental solvolysis rates (ln k) and the B3LYP/6-31G(d)-computed ionization energies (ΔE) of the corresponding bridgehead hydrocarbons in gas phase. However, this work demonstrates the existence of a fair linear correlation between the experimental reaction rates and the PCM//B3LYP/6- 31G(d)-computed free ionization energies in solution (ΔG). This theoretically relevant result reveals that the reason for the lack of linearity in gas phase is not the rearrangement of the intermediate carbocations but unspecific solvent effects on the solvolysis rates, accounted for by the PCM model. Introduction Solvent Effects on the Relative Solvolysis Rates of Sub- stituted 1-Norbornyl Triflates. Solvent effects are of para- mount importance in organic chemistry. 1 There is a great deal of work dedicated to the experimental study of solvent effects on the solvolysis rate of several substrates, mainly in relation to the Grunwald-Winstein equation, 1,2 but not in the case of Schleyer’s relationship of rate constants (ln k) vs thermodynamic stability of the involved carbocations in gas phase. 3 Probably due to canceling errors, good relationships are obtained inde- pendently of the method used for the definition of the carboca- tion thermodynamic stability. Originally, this stability was expressed by the difference in strain energy between the bridgehead carbocation and the corresponding hydrocarbon, calculated by molecular mechanics methods. 3 Later, the calcula- tion of strain energies of bridgehead carbocations was based on dissociation energies of the corresponding bromides, 4 isodes- mic reactions, 5 or free energies of the proton- or bromide- transfer reactions in the gas phase. 6 The proper state function * To whom correspondence should be addressed. Phone: +91 3944333. Fax: +91 3944103. † Facultad de Ciencias, Universidad Nacional de Educacio ´n a Distancia (UNED), Senda del Rey 9, 28040 Madrid, Spain. (1) Reichardt, C. SolVents and SolVent Effects in Organic Chemistry; Wiley- VCH: Weinheim, 2002. (2) (a) Shorter, J. Correlation Analysis of Organic ReactiVity; Research Studies Press: Chichester, 1982. Also see: (b) Mayr, H.; Ofial, A. R. Angew. Chem., Int. Ed. 2006, 45, 1844–1854. (3) (a) For reviews, see: Fort, R. C.; Schleyer, P. v. R. In AdVances in Alicyclic Chemistry; Academic Press: New York, 1966; Vol. 1, pp 284-370. (b) Fort, R. C.; Schleyer, P. v. R. In Carbonium Ions; Wiley-Interscience: New York, 1973; Vol. IV, pp 1783-1835. (4) For reviews, see: (a) Mu ¨ller, P.; Mareda, J. In Cage Hydrocarbons; Wiley- Interscience: New York, 1990; pp 189-217. (b) Mu ¨ller, P.; Mareda, J.; Millin, D. J. Phys. Org. Chem. 1995, 8, 507–528. (5) (a) Hrovat, D. A.; Borden, W. T. J. Am. Chem. Soc. 1990, 112, 3277– 3228. (b) Della, E. W.; Janowski, W. K. J. Org. Chem. 1995, 60, 7756–7759. (6) (a) Mu ¨ller, P.; Millin, D.; Feng, W. Q.; Houriet, R.; Della, E. W. J. Am. Chem. Soc. 1992, 114, 6169–6172. (b) Abboud, J. L.; Herreros, M.; Notario, R.; Lomas, J. S.; Mareda, J.; Mu ¨ller, P.; Rossier, J. C. J. Am. Chem. Soc. 1999, 64, 6401–6410. 10.1021/jo8009787 CCC: $40.75  2008 American Chemical Society J. Org. Chem. 2008, 73, 6607–6614 6607 Published on Web 08/06/2008