J. Org. Chem. 1983,48, 2029-2035 the peak height of ABMeP-0 at infinite time when the rearrangement went to completion. In several earlier cases, before gated decoupling was used, concentrations obtained for the phosphonium intermediate were much too high as result of great nuclear Overhauser enhancement of the intermediate peak relative to the reactant and product. It was necessary to adjust these concentrations by using the material balance. The chemical shifts for the phosphonium intermediates ABMeP+OMeX-are, with substituents A and B followed by the parenthsized chemical shifts, mmured in ppm downfield from phospharic acid Et, OMe (98);Ph, OMe (79) (both in CD3CN)and t-Bu, t-Bu (108); t-Bu, OMe (98) (in CDC13).
Rate Constant Calculation The rough experimental concentration vs. time curves for ABPOMe, ABMeP+OMeX-,and ABMeP=O were smoothed and the data points evenly spaced over time by using a variable-order polynomial fit routine.lS The differential equations 4-7 describing the rearrangement were integrated by using fourth-order Runge Kutta numberical techniquedB and a theoretical concentration (18) Shoemaker, D. P.; Garland, C. W. ‘Experiments in Physical Chemistry”, 3rd ed.;McGraw Hill: New York, 1974. (19) Camahan, B.; Luther, H. A,; Wilkes, J. 0. ‘Applied Numerical Methods”; Wiley: New York, 1969.
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vs time curve constructed for each of the phosphorus-containing species. Using iterative techniques adapted from those of Wiberg,2othe “best”rate constants were obtained by minimizing the root-mean-square error between one of the theoretical curves and the correspondingexperimental one. The rate constants shown in Table III are those that gave the lowest root-mean-square eror for all three of the curves. A graphics display similar to that in Figure 2 was used to subjectively select the most satisfactory constants when the program encountered a braod root-meansquare error minimum.
Acknowledgment. We thank the Robert A. Welch Foundation for a grant supporting this work and providing a fellowship to Donald Hamp. The phosphorus NMR spectra were taken on an instrument partially paid for by a research instrument grant from the National Science Foundation. Registry No. CH3P(OCH3)2,20278-51-7; PhP(OCH3)2, 2946-61-4;EtP(OCH3)2, 15715-42-1;t-BuP(OCHJ2, 32045-17-3; PhZPOCH3, 4020-99-9; (~-Bu)~POCH~, 70073-11-9; P(OCH& 121-45-9;methyl triflate, 333-27-7; dimethyl sulfate, 77-78-1; methyl iodide, 74-88-4. (20) Wiberg, K. B. In ‘Techniques of Chemistry”; Lewis, E. S., Ed; Wiley: New York, 1974; Vol. pp 6, 741-776.
Circular Dichroism Studies on Three Isomeric Dimethylbenzo-15-crown-5 Ethers and Some of Their Complexes’ Mark P. Mack, Richard R. Hendrixson, Richard A. Palmer,* and Robert G. Ghirardelli* Paul M.Gross Chemical Laboratory, Duke University, Durham, North Carolina 27706
Received December 7, 1982 With ethyl lactate as an optically active precursor and with employment of Williamson reactions, three isomeric and axially symmetric dimethylbenzo-15-crown4ethers were prepared and characterized: (5R,15R)-5,15-dimethyl-5,6,8,9,11,12,14,15-octahydrobenzo[b]-1,4,7,10,13-pentaoxa~clopentad~in and the (6S,14S)-6,14-dimethyl and (8S,l2S)-8,12-dimethylisomers, termed the a,8, and y isomers, respectively. The circular dichroism spectra of the ethers and their complexes with Na+ in CH30H have been determined and interpreted in terms of the gross overall orientation of the macrocycle in relation to the aromatic ring. The behavior of the y isomer with Ba2+and with low ratios of K* suggests dominance of 2:l (sandwich) complexes. The macrocyclic polyethers2 have provided chemists with a fruitful territory for exploration since the initial comprehensive report3 of their properties of 1967. Like their relatives the cyclic polypeptides and polyesters, the polyethers (dubbed “crowns” by Pedersen, their discoverer/inventor) possess the ability to moderate the inhospitality which nonpolar solvents ordinarily display toward ionic species. The charge on the cations is dispersed by the complexand or ionophore, which, depending on the match in sizes, can encircle or envelop the ion. The interaction between the two is clearly ion-dipole in the case of cations of main groups 1 and 2, involves hydrogen
bonding in the case of ammonium ions, and possesses a t least some degree of covalent character in the case of the transition metals.4 In polar media there exists, of course, a competition for the cation between solvent and macrocycle; which interaction dominates will depend on the nature of the particular solvent, salt, and complexand and will govern the stability of the complex under the specific circumstances. A number of crown ether complexes have been prepared in crystalline form, and X-ray diffraction5 has been employed to establish the spatial relationship of macrocycle to cation, as well as the conformation of the former.
(1) Reported in part at the 174th National Meeting of the American Chemical Society, Chicago, IL, Sept 1977. Some of the studies with compound 3 have been subjecta of an earlier communication: Mack, M. P.; Hendrixson, R R.; Palmer, R. A.; Ghirdelli, R. G. J.Am. Chem.SOC. 1976,98,7830. (2) For general reviews see: (a) Gokel, G. W.; Durst, H. D. Synthesis 1976. 168. (b) Izatt, R. M.: Christensen, J. J., Eda. ‘Synthetic Multident& Ma&&clic Compoknds”; Academic Press: New-York, 1978. (c) Ddong, F.; Reinhoudt, D. N. Adv. Phys. Org. Chem. 1980,17,279. (3) Pedersen, C. J. J.Am. Chem. SOC.1967,89, 7017.
(4) C. L. Liotta has discussed these interactions in terms of the hardness and softness of the participating species: 9th Central Regional Meeting of the American Chemical Society, Charleston, WV, Oct 1977. (5) The parent compound to those of this study has been the subject of several: (a) Bush, M. A.; Truter, M. R. J.Chem. SOC.,Perkin Trans. 2 1972, 1818. (b) Owen, J. D.; Wingfeld, J. N. J. Chem. SOC.,Chem. Commun. 1976,318. (c) Cradwick, P. D.; Poonia, N. S. Acta Crystallogr., Sect. B 1977, B33, 197. (d) Owen, J. D. J. Chem. Soc., Dalton Trans. 1978, 1418. (e) Hanson, I. R. Acta Crystallogr., Sect. B 1978 B34,1026. (f) Owen, J. D. J. Chem. SOC.,Dalton Trans 1980, 1066.
0022-3263/83/1948-2029$01.50/00 1983 American Chemical Society
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J. Org. Chem., Vol. 48, No. 12, 1983
Mack et al. Scheme I
+ r \ O H
IMeOH H+
t P 3 HO
OH
o-C6H4(0CH2C1420Na)2
Naturally, lattice forces come into d a v under these circumstances, and there is an anion to kcbmmodate as well. On the other hand, the situation in dilute solution, using solvents which can effectively solvate the anion, can be quite different. A limited number of studies have addressed the question of cyclic polyether conformation in solution, which is where these compounds manifest their more interesting properties. Here spectroscopic techniques, requiring interpretation less straightforward than X-ray crystallography, must be employed. In his pioneering experiments3Pedenen used ultraviolet absorption spectroscopy as a qualitative measure of complex formation. More recently Dale has drawn some conformational conclusions from infrarede data and, in a study of a tetraoxacyclododecane carried out with Anet, from NMR spectroscopy.' This last technique provided the basis for a detailed examination of dibenzo-18-crown-6 by Chan8 Lockhartg has recently published an analysis of the proton NMR spectra of several crowns and their complexes, including the parent of those described in this paper. Grunwaldlo determined electric dipole moments and drew some conclusions about the conformations of crown complexes in octanoic acid solution, where it is evident that a considerable amount of ion-pairing between metal ion and counteranion persists. The conformation of the 12membered polyether ring bound to lithium ion was subjected to a theoretical treatment by Pullman.'l Given an optically active substrate, circular dichroism (CD) spectroscopy,12which measures the differential absorption of right and left circularly polarized light, can potentially provide considerably more information than is available from simple absorption techniques. As part of what we hope to develop into a systematic effort to use (6) Dale, J.; Kristiansen, P. 0.Acta Chem. Scand. 1972, 26, 1471. (7) Anet, F. A. L.; b a n e , J.; Dale, J.; Daasvatn, K.; Kristiansen, P. 0. Acta Chem. Scand. 1973, 27, 3395. For a more recent review: Dale, J. Isr. J . Chem. 1980,20, 3. (8)Live, D.; Chan, S. I. J . Am. Chem. SOC.1976,98,3769. (9) Lockhart, J. C.; Robson, A. C.; Thompson, M. E.; Tyson, P. D.; Wallace, I. H. M. J. Chem. Soc., Dalton Trans. 1978, 611. (10)I, T.-P.; Grunwald, E. J. Am. Chem. SOC.1974,96, 2879. (11) Pullman,A.; Giessner-Prettre, C.; Kruglyak, Y. V. Chem. Phys. Lett. 1975, 35, 156. (12) Crabbe, P. "ORD and CD in Chemistry and Biochemistry";Academic Press: New York, 1972. Snatzke, G., Ed. 'Optical Rotatory Dis-
persion and Circular Dichroism in Organic Chemistry";Heyden: London, 1967. Djerassi, C. Proc. Chem. SOC.,London 1964, 314.
CD spectroscopy to study polyether conformation and related properties, three isomeric cyclic polyethers (1-3)
v .fly
