Spatial orientation effects on the σ-assistance in the solvolysis of methyl substituted 1-norbornyl triflates

Effects of Bridgehead Metalloidal Substituents (MMe3, M = Si and Sn) on the Stability of the 1-Norbornyl Cation

“…The weak accelerative effect for Me in 1 (Y = OSO 2 CF 3 ; Table ), previously noted by Martinez et al, 11b, is of particular interest because it stands in stark contrast to the feeble decelerating effects of this group in 2 and 3 ( 2 , Y = p -NO 2 C 6 H 4 SO 2 O, Me/H = 0.25 (80E); 3 , Y = Br, Me/H = 0.74 (80E);1a 3 , Y = p -CH 3 C 6 H 4 SO 2 O, Me/H = 0.78 (80E)) . The results for the latter two systems are in line with a large body of NMR and reactivity data from polycycloalkane model system ,− studies on γ- and δ-effects which suggests that Me is a weak σ-electron withdrawing group.…”

Solvent and Stereoelectronic Effects on the Solvolysis Rates of Oxaspirocyclopropanated 1-Norbornyl Triflates and Related Bridgehead Derivatives

“…The previously described solvolysis of related 1-norbornyl triflates 1(OTf)-4(OTf) (Figure 1), under analogous reaction conditions, gave place to the corresponding unrearranged bridgehead alcohols and ethers (60/40 ratio). 11a, 13 Unexpectedly, only rearranged alcohols were isolated in the solvolysis of the oxaspirocyclopropanated 5(OTf)-8(OTf) (see Scheme 1 and Table 1). The formation of such rearranged reaction products could be explained according to the reaction pathways proposed in Scheme 2.…”

“…Table 2 shows the found k values. Previously reported data for related triflates 1(OTf)-3(OTf) 13 and 4(OTf) 11a have been introduced in Table 2 for comparison. The reported extrapolated values were calculated from k values obtained at three different temperatures in the range 333-373 K.…”

“…A mixture of epimeric 5(OTf) and 6(OTf) (44:56 by 1 H NMR) was obtained by standard epoxidation of (-)-fenchone-derived (1R)-3,3-dimethyl-2-methylenenorborn-1-yl triflate with m-CPBA and resolved by elution chromatography according to the procedure described previously by us. 13 C NMR (CDCl 3 , 50 MHz) δ: 118.4 (c, J ) 319.0 Hz, CF 3 ), 96.0, 69. 7, 45.6, 43.3, 38.9, 37.8, 30.4, 24.2, 23.8, 23.5 1 H NMR (CDCl 3 , 200 MHz) δ: 3.05 (AB, d, J ) 4,4 Hz, 1H), 2.83 (AB, d, J ) 4.4 Hz, 1H), 2.46 (ddd, J ) 9.7 Hz, J ) 3.9 Hz, J ) 2.0 Hz, 1H), 2.24 (dd, J ) 10.0 Hz, J ) 2.0 Hz, 1H), 2.24-1.79 (m, 5H), 1.08 (s, 3H), 0.87 (s, 3H) ppm.…”

“…7, 45.6, 43.3, 38.9, 37.8, 30.4, 24.2, 23.8, 23.5 1 H NMR (CDCl 3 , 200 MHz) δ: 3.05 (AB, d, J ) 4,4 Hz, 1H), 2.83 (AB, d, J ) 4.4 Hz, 1H), 2.46 (ddd, J ) 9.7 Hz, J ) 3.9 Hz, J ) 2.0 Hz, 1H), 2.24 (dd, J ) 10.0 Hz, J ) 2.0 Hz, 1H), 2.24-1.79 (m, 5H), 1.08 (s, 3H), 0.87 (s, 3H) ppm. 13 C NMR (CDCl 3 , 50 MHz) δ: 118.2 (c, J ) 319.0 Hz, CF 3 ), 97.2, 70.9, 49.5, 43.5, 38.1, 38.0, 27.3, 27.2, 24.3, 21. Supporting Information Available: General experimental information, optimized geometries (Cartesian coordinates), as well as 1 H and 13 C NMR spectra for the new described compounds. This material is available free of charge via the Internet at http://pubs.acs.org.…”