J. Am. Chem. SOC.1993,115, 12010-12015
12010
Coupling Constants in Carbocations. 7.’ Application of the AJ Equation to Polycyclic Systems Including Bicycle[ 2.2.13hept-2-yl Cations 13C-lH
David P. Kelly,’ Kathryn Aherne, Florencio Delgado, Joseph J. Giansiracusa, Wendy A. Jensen, Kelly Karavokiros, Robert A. Mantello, and Monica E. Reum Contribution from the School of Chemistry, The University of Melbourne, Parkville. Victoria 3052, Australia Received June 14. 1993’
Abstract: One-bond 13C-lH coupling constants have been measured for the polycyclic carbocations 2-methylbicyclo[2.2.2]octyl (lo), 2-arylbicycloI2.2.2]octyl(ll), 3-arylbicyclo[3.2.1]octyl(15), 8-methyltricyclo[5.2.1.02v6]decyl(23), 2-methyl-5,6-benzobicyclo[2.2.l]heptyl(25). 2-arylbicyclo[2.2.1]heptyl (27),2-methyltricyclo[3.3.1.13~7]decyl (17), and 2-aryltricyclo[3.3.1.13,7]decyl(18). Comparisons with the corresponding ketones provided AJ values consistent with classical cations for 10,11,15,23,and 25. In the case of 17 and 18 the low AJ values suggest that 2-adamantyl cations are distorted significantly from sp2 toward sp3 hybridization. AJQH values for 27 give an excellent linear correlation with u+, with no deviation at high electron demand. For the parent 2-norbornyl cation (28),exceptionally high values for AJ are consistent with a nonclassical a-bridged structure in superacid.
Introduction The AJequations (1) and (2), which relate the one-bond I3ClH coupling constant of a group adjacent to a positive charge in a carbocation to the amount of charge and to the dihedral angle between the C-H orbital and the vacant pT have been used successfully to determine the structures of acyclic, cyclic, and bicyclic cations generated in superacidsaZ4
AJ = 22.5 - 33.1 cos’ 9
(1)
AJ = (1 + 0.6~+)(10.9- 14.3 cosz e)
(2) In the case of internal cyclopropylcarbinylcations, e.g. bicyclo[4.1.O]heptyl systems, it allowed the determinationof the structure of the rearranged ion from 1,6-methano[lO]ann~lene.~.~ The value of 24 Hz for AJQH of this cation (1) is consistent with a 90” dihedral angle for C2-H and a static bisected, cyclopropylcarbinyl structure. In equilibrating classical systems, AJ for the group adjacent to the equilibrating center, e.g. C1 in 2, is approximately half that predicted by eq 1 for static cations as a result of sharing of the positive charge between C2 and C3.
1
2
3
In dialkyl aryl cations, AJ is sensitive to the amount of charge at the adjacent carbon 2s measured by u+ in eq 2.3 Replacing Abstract published in Aduance ACS Abstracts, October 15,-H at -159 OC, 188 H z . ~This ~ represents a massive increase over J C ~ofH2-norbornanone (148 Hz), much greater than predicted by eq 1, greater than those observed in uu-bridged cations, and consistent with the idea of increasing ~~~
~
~~~~
(36) JCHvalues for some of these cations have been reported previ~usly.~ Additional data are provided in Table 1. (37) Giansiracusa, J. J.; Jenkins, M. J.; Kelly, D. P. Ausr. J. Chem. 1982, 35, 443-450. (38) (a) Olah, G. A.; Prakash, G. K. S.; Farnum, D. G.; Clausen, T. P. J. Org. Chem. 1983,48,2146-2151. (b) Olah, G. A.; Prakash, G. K. S.; Liang, G. A. J. Am. Chem. SOC.1977, 99, 5683-5687. (39) Farnum,D. G.; Wolf,A. D. J. Am. Chem.Soc. 1974,96,5166-5175. (40) For reviews, see: (a) Grob, C. A. Acc. Chem. Res. 1983,16,426-43 1. (b) Br0wn.H. C. Ace. Chem.Res. 1983,16,432440. (c) Olah,G. A.;Prakash, G. K. S.; Saunders, M. Ace. Chem. Res. 1983,16,440-448. (d) Walling, C. Ace. Chem. Res. 1983, 16, 448454. (41) (a) Saunders, M.; Johnson, C. S. J. Am. Chem. SOC.1987,109,44014402. (b) Koch, W.; Liu, B.; De Frees, D. J. J. Am. Chem. SOC.1989,111, 1527-1 528. (42) (a) Myhre, P. C.; Webb, G. G.: Yannoni, C. S . J. Am. Chem. SOC. 1990.112,8991-8992. (b) Laube, T. Angew. Chem., Inr. Ed. Engl, 1987,26, 560-562. (43) Olah, G. A.; Prakash, G. K. S.;Arvanghi, M.; Anet, F. A. L. J. Am. Chem. Soc. 1982, 104,7105-7108.
4 “
1
-1
;
I
1
;
Q+
Figure 1. Correlation of A J c ~ Hwith electron demand in 2-arylbicyclo[2.2.l]heptylcations27(correlationcoeffcient0.993;for 0.988).
e+,?=
internal strain accompanying u-bridge formation as originally proposed.44 In fact J c I 3has ~ the same value as that for C1,6 in the 3-methylnortricyclyl cation and is consistent with the formation of a three-memberedring bearing positivecharge.Thus application of the A J equation supports a a-bridged nonclassical structure for the secondary 2-norbornyl cation. The A J equation is thus useful in determining the structure of carbocations in superacids. Low values of AJ result from equilibration as in the case of 2 or from distortion of the idealized geometry. In the case of 17 this provides additional evidence to support a hypothesisthat these cations are distorted significantly from sp2 toward sp3(pyramidal) hybridization. Relatively high values of A J are associated with the formation of nonclassical structures, as a result of r-bridging (4), Tu-bridging (a), or u-bridging (28).
Experimental Section
NMR Spectra. The proton and carbon N M R spectra were recorded on a variety of instruments under conditions as described previously.5 Chemical shifts of cationic solutions in superacids were measured from external (capillary) Me& Coupling constants (t1 Hz) were measured by hand from expanded plots. In some c a w of complex spectra, selective excitation (DANTE) or editing (coupled DEPT) techniques were employed to obtain JCH values from overlapping signals. Synthesis. Bicyclo[3.2.l]octan-2-one,adamantanone (19), bicycle[3.3.1 ]nonan-9-one, 2-norbornanone (22), and tricyclo [5.2.1 .02v6]decan8-one (24)@werecommercially available (Aldrich). Bicyclo [2.2.2]octan24ne (12)p5 bicycle[ 3.2.l]octan-6-0ne,~bicyclo[3.2.11octan-3-0ne (13):’ and benzonorbornan-Zone (26)49 were prepared according to literature procedures. 3-Arylbicyclo[3.2.1]ocCaP3-ols were prepared from 13by reactionwith the appropriate arylmagnesium bromide, the unreacted ketone was removed under vacuum, and the products were recrystallized from petroleum ether (60-80 “C). 14b, white needles (43%), mp 84-85 OC, vmx 3460 cm-’; 6 IH (CDCl3) 7.2-7.5 (m, 4H), 3.8 (s, 3H, OCHn), 1.5-2.8 (m, 12H); 6 13C(CDCl3) 35.0 (d, C1,5), 47.3 (t, C2,4), 74.2 (s, C3), 28.4 (C6,7), 143.4 (s, Cl’), 125.6 (d, C2’,6’), 113.3 (d, C3’,5’), 157.9 (s, C4’), 55.1 (9,OCH3); MS m/z (5%) 232 (M+, 40), 214 (37), 185 (63), 150 (100). Anal. Calcd for C1sH2002: C, 77.6; H, 8.7. Found: C, 77.6; H, 8.8. 14c, white plates (64%), mp 109-110 OC, urmX 3460 cm-I; 6 ‘H (CDC13) 7.1-7.5 (m, 4H), 2.30 (s, 3H), 1.4-2.4 (m, 11H). 6 13C (CDC13) 35.0 (d, C1,5), 47.4 (t, C2,4), 74.5 (s, C3), 28.5 (t, C6,7), 135.8 (s, Cl’), 128.7 (d, C2’,6’), 124.4 (d, C3’,5’), 148.2 (s, (44) (a) Kelly, D. P.; Brown, H. C. J. Am. Chem. SOC.1975.97, 38973900. (b) Olah, G. A.; Kelly, D. P.; Jeuell, C. J.; Porter, R. D. J. Am. Chem. Soc. 1970, 92, 2544-2548. (45) Alder, K.; Krieger, H.; Weiss, H. Chem. Ber. 1955, 88, 144-155. Freeman, P. K.; Nalls, D. M.; Brown, D. J. J. Org. Chem. 1968, 33, 22112214. Mislow, K.; Berger, J. G. J. Am. Chem. Soc. 1962, 84, 1956-1961. (46) Ipatieff, V. N.; Germain, J. E.; Thompson, W. W.; Pines, A. J. Org. Chem. 1952, 17, 272-285. (47) Kraus, W.; Klein, G.; Sadlo, H.; Rothenwahrer, W. Synthesis 1972, 485487. (48) Brown, H. C.; Vander Jagt, D. L.; Schleyer, P. v. R.; Fort, R. C.; Watts, W. E. J. Am. Chem. SOC.1969, 91, 68484850. (49) Miiller, P.; Blanc, J. Helu. Chim. Acta 1979, 62, 1980-1984.
Application of the AJ Equation to Polycyclic Systems
J. Am. Chem. SOC.,Vol. 115, No. 25, 1993 12015
Table II. 13C NMR Chemical Shifts for 2-Arylbicyclo[2.2.2]octan-2-ols aryl substituent
C1
C2
C3
C4
C5
C6
C7
C8
C1’
C2’
C3’
C4‘
C5’
C6’
CX
3’,4’-CH2CH2@
32.5
132.5
121.4
30.5
25.8
26.9
25.8
26.9
144.6
124.5
127.1
159.1
109.1
126.8
4’-OMea 4’-Me 4’-Cl H 3/43 4’-CF3
32.2 35.9 35.9 35.9 35.9 36.0
132.3 74.9 74.7 75.1 74.9 74.9
127.2 42.1 42.0 42.0 42.0 41.9
30.4 26.0 25.7 25.9 25.7 25.7
25.9 21.1 20.9 21.1 21.0 20.8
26.2 24.3 24.0 24.2 24.1 23.8
25.9 22.5 22.2 22.4 22.2 22.1
26.2 25.1 24.9 25.1 24.9 24.7
144.2 136.4 132.4 148.0 150.2 152.1
125.7 128.7 127.9 128.0 126S6 126.4
113.8 125.9 127.5 126.0 134.0 125.3
158.5 145.1 146.4 126.6 129.2b 129.0
113.8 125.9 127.5 126.0 124.2 125.3
125.7 128.7 127.4 128.0 126.96 126.4
29.9 71.3 55.3 20.9
~~
a
124.5
Alkene. Assignments may be interchanged.
C4’), 20.8 (q, CHI). MS m/z (%) 216 (M,+, 34), 201 (42), 134 (100). [2.2.2]octan-2-01,~~*~~ after distillation a viscous oil, bp 110-120 OC/2 Anal. Calcd for C15H200: C, 83.3; H, 9.3. Found: C, 83.5, H 9.0.14e, mmHg, vmx 3300, 2950 cm’; 6 ‘H (CDC13) 7.2-7.8 (m, 4H), 1.1-2.7 white plates (77%), mp 80-81 “ C ,vmax 3460,3020 cm-l; 6 ‘H (CDClp) (m, 12H). 7.2-7.5 (m, 5H). 1.5-2.8 (m, 12H). 6 I3C (CDCl3) 35.0 (d, C1,5), 47.4 The syntheses of the 2-aryltri~yclo[3.3.1.l~~]decan-2-ols, precursors (t, C2,4), 74.6 (s, C3), 28.5 (t. C6,7), 38.6 (t, C8), 151.1 (s, Cl’), 128.0 of cations 18, have been reported in the l i t e r a t ~ r e . ~ ~ .Previously ~’,~~ unreported 13CNMR chemical shifts for these alcohols are tabulated in (d, C2’,6’), 123.5 (d, C3’,5’), 126.2 (d, C4’). MS m/z (%) 202 (M,+, 36), 173 (9), 159 (15), 145 (lo), 120 (100). Anal. Calcdfor C14H180: C, the supplementary material. 83.1;H,9.0. Found: C,83.7;H,8.5. 14g,whiteplates(35%),mp67-68 8 - M e t h y l - ~ ~ e x o - ~ ~ h s ~ y c l o [ Swas . Z prepared . l . ~ ~from ~~ ketone 24 by treatment with methylmagnesiumiodide. Recrystallization “ C , vmax 3460, 3040 cm-I; 6 ‘H (CDCl3) 7.3-7.8 (m, 4H), 1.5-2.5 (m, (pentane) yielded the alcohol as white needles, mp 79-81 OC (lit.4881.512H). 6 13C (CDC13) 35.0 (d, Cl,5), 47.5 (t, C2,4), 74.5 (s, C3), 28.5 82 “C), 6 ”C (CDCl3) 27.9 (C4), 30.3 (CHp), 31.7 (C3), 32.4 (ClO), (t,C6,7), 38.5 (t,C8), 152.2(s,Cl’), 123.3 (q,C2’or4’), 129.5 (s,C3’), 121.6 (q, C4’or 2’), 128.0 (d, C5’ or 6’), 128.6 (d, C6’ or 5’), 124.4 (q, 32.6 (CS), 39.2 (C2), 41.7 (C6), 46.5 (C9), 46.7 (Cl), 52.7 (C7), 76.9 CF3). MS m / z (%) 270 (M,+, 32), 252 (15), 227 (12), 201 (lo), 189 (C8). (31), 188 (100). Anal. Calcd for C I S H I ~ O FC, ~ :66.7; H, 6.3. Found: The syntheses of the alcohol precursors to cations 27a-e have been C, 67.3; H, 6.3. 14h, pale-yellow needles (52%), mp 122 OC, umax 3460 reported.20~50*s2 However, we now quote the previously unreported 13C N M R spectral data for the following alcohols: cm-I; 6 ‘H (CDCl3) 7.56 (s, 4H), 1.6-2.4 (m, 12H). 6 ”C (CDC13) 34.9 (d, C1,5),47.5 (t, C2,4), 74.8 (s, C3), 28.5 (t, C6,7), 38.6 (t, C8), 155.0 2-(3’,4’-(Ethylewoxy)pbenyl)-2-~bicyclo[2.Z.l~pt.wl,after distillation and recrystallization, a white solid, mp 71-74 OC (lit.5o75-76 (s, Cl’), 125.1 (d, C2’,6’), 124.9 (d, C3’,5’), 129.3 (s, C4’), 124.3 (q, “ C ) ;6 I3C (CDCl3) 22.2 (C5), 29.7 (C6), 37.6 (C4), 38.7 (C7), 46.7 CF3). MS m / z (%) 270 (M.+, 29), 201 (42), 187 (lo), 173 (15), 169 (C3), 47.3 (Cl), 80.6 (C2). 29.1 (CH2CH20), 71.3 (CH2CH20), 108.4 ( l l ) , 134 (100). Anal. Calcd for ClsH~70F3:C, 66.7; H, 6.3. Found: ( C Y ) , 122.8 (CZ’), 125.4 (C6’), 126.9 (C3’), 141.4 (Cl’), 158.8 (C4’). C, 67.0; H, 6.4. Z-ArylbicycloI2.2.Z]oc~~2-ols were prepared from 12 by reaction with 2-(4’-Fluorophenyl)-2-e~~ebicyclo[Z.2.l]heptrwlas white crystals, the appropriate aryl magnesium bromide. Distillation and/or recrysmp 63-64 OC (lit.5263-64 “ C )6 I3C(CDCl3) 47.4 (Cl), 80.4 (C2), 46.9 tallization gave the required alcohol. Some products were contaminated (C3), 37.6 (C4), 22.3 (CS), 29.0 (C6), 38.7 (C7), 144.9 (Cl’), 127.6 by the corresponding olefin, a result of dehydration during purification (C2’,6’), 114.9 (C3’,5’), 161.6 (C4’). procedures. For the purposes of cation generation, however, the presence 2-(3’-Methylphenyl)-2-~~ebicycl~2.2.l~p~nol as white crystals, of alcohol/olefin mixtures can be tolerated, since both afford the same mp 57-58 OC; 6 13C(CDC13) 47.2 (Cl), 80.7 (CZ), 46.5 (C3), 37.5 (C4), cation upon protonation in superacid media. The ”C chemical shifts for 22.2 (C5), 29.1 (C6), 38.7 (C7), 137.8 (Cl’), 126.7 (CZ’), 149.0 (C3‘), the2-arylbicyclo[2.2.2]octan-2-olsare presented inTable 11. Apart from 128.1 (C4’), 122.7 ( C Y ) , 127.5 (C6’), 21.6 (CHI). Anal. Calcd for the 2-(3’,4’-ethyleneoxyphenyl) derivative, the 2-arylbicyclo[2.2.2]ClrHl80: C, 83.1; H, 9.0. Found: C, 83.5; H, 9.1. 2-(3’-Chlorophenyl)-2-en&bicyclo[2.2.l]heptnnol as white crystals, octanols have been described mp 39-41 OC (litS242-44 O C ) ; 6 I3C (CDCl3) 47.3 (Cl), 80.5 (CZ), 46.8 2-(3’,4’-(Ethyleneoxy)phenyl)bicycl~2.2.2~t-2-ene was prepared by reaction of 12 with 5-lithio-2,3-dihydrobenzof~ran,~~ followed by workup (C3), 37.6 (C4), 22.3 (C5), 28.9 (C6), 38.8 (C7), 158.2 (Cl’), 126.4 (C2’), 134.1 (C3’), 129.5 (C4’), 124.1 ( C Y ) , 126.9 (C6’). and dehydration. Distillation afforded the title compound as a viscous yellow oil, bp 125-135 OC/O.3 mmHg,vmx2850, 1590,1470,1210cm-’; 2-Phenyl-2-endebicyclo[Z.2.1]heptanolas white crystals, mp 4 W 2 6 ‘H (CDCl3) 7.1 (d, 2H), 6.7 (s, lH), 6.3 (d, lH), 4.5 (t, 2H), 3.1 (t, OC (lit.5241-42“C); 6 I3C(CDCl3) 47.3 (Cl), 80.8 (C2),46.7 (C3), 37.7 (C4). 22.5 (C5), 29.3 (C6), 39.0 (C7), 149.2 (Cl’), 128.4 (C2’,6’), 126.1 2H), 1.2-1.9 (m, 10H). (C3’,5’), 126.9 (C4’). 2-(4’-Methoxyphenyl) bicyclo[2.2.2]octan-2-0I,~~~~~ after distillation a yellow oil, bp 110-120 OC/O.2 mmHg, vmx 3400 cm-I. 2-(4’2-(3’-(Tri~oromethyl)phenyl)-2-endebicyclo[2.2.l]hept.wlas white crystals, mp 47-48 O C ; 6 I3C (CDCI,) 47.4 (Cl), 80.6 (CZ), 46.9 (C3), Methylphenyl)bicyc~2.2.2~-2-0l~~~~~afterdistillation anoil, bp 123125 O C / O . 5 mmHg, vmx 3400, 2920 cm-I; 6 ‘H (CDCl3) 6.9-7.4 (m, 37.6 (C4), 22.2 (C5), 28.9 (C6), 38.8 (C7), 150.0 (Cl’), 122.8 (q, 3, 4H), 2.3 (s, 3H), 1.0-1.9 (m, 12H). 2-(4’-Chlorophenyl)bicyclo[2.2.2]C2’), 130.5 (q, 32, C3’), 123.6 (9. 4.4, C4’), 128.7 ( C Y ) , 129.5 (Cat), 124.4 (q, 273, CF3). Anal. Calcd for C I ~ H ~ S O C, F ~65.6; : octan-2-0I,~~ after distillation a viscous oil, bp 125-135 OC/2 mmHg H, 5.9; F, (lit.52 125-145 OC/3 mmHg), vmX 3380,2920 cm-I; 6 ‘H (CDCl3) 7.122.2. Found: C, 65.9; H, 6.1; F, 22.4. 7.4 (m, 4H), 1.3-2.5 (m. 12H). 2-PhenylbicycIo[2.2.2]oc~n-2-0l,~~~~~ Acknowledgment. This work was supported by the Australian after distillation a viscous oil, bp 95-100 OC/O.2 mmHg (litS2135-152 OC/15 mmHg), vmax 3380, 2920 cm-’; 6 ‘H (CDCl3) 7.1-7.5 (m, 5H), Research Grants Committee. 1.3-2.5 (m, 12H). 2-(3’-Chlorophenyl)bicy~lo[2.2.2]octan-2-ol,~~ after SupplementaryMaterial Available: Table of I3Cchemical shifts distillation a viscous oil, bp 115-120 OC/O.5 mmHg (litS260 OC/O.3 mmHg, molecular distillation), vmX 3350,2900 cm-I; 6 ‘H (CDC13) 7.0of 2-aryltricyclo[3.3.1.13,’]decan-2-ols(2 pages). Ordering in7.5 (m, 4H), 1.2-2.5 (m. 12H). 2-(4’-(Trifluoromethyl)phenyl)bicycloformation is given on any current masthead page. (50) Brown, H.C.; Gundu Rao, C. J. Org. Chem. 1979, 44, 133-136. (51) IH and 13CNMRdata for this alcohol are available as supplementary material from: Forsyth, D. A.; Panyachotipun, Y. P.; Moussa,A. M.; Youssef, A.-H. A. J. Org. Chem. 1990, 55, 5375-5386. (52) The preparation of this compound (or the corresponding olefin) has been previously reported, and selected physical data are available: Farnum, D. G.; Wolf, A. D. J. Am. Chem. Soe. 1974, 96, 5166-5175.
(53) The preparation of this compound has been previously reported, and selected physical data are available: Wolf, A. D.; Farnum, D. G. J. Am. Chem. Soe. 1974, 96, 5176-5181. (54)Liu, K.-T.; Sheu, H.-C. J. Org. Chem. 1991, 56, 3021-3025. Krishnamurthy, V.V.;Iyer, P. S.; Olah, G. A. J. Org. Chem. 1983,48,33733378. Duddeck, H.; Hollowwd, F.; Karim, A.; McKervey, M. A. J. Chem. Soe., Perkin Trans. 2 1979, 360-365.
