m u
4669
1MS
ft
150
IO0
PPM
50
Figure 1. Assumed structure for the ice-lh crystal.'
systems, by Schleyer and Engler, 143. indicated that the saturated hydrocarbon derived from 6 was approximately 8.7 kcal/mol less stable than iceane itself, and thus our desired rearrangements were thermodynamically favorable. 1 2 b Treatment of 6 for 8 hr at 120" with 3 0 x HBr-HOAc gave 10 (72 % yield) which was reduced, without further
fj -+
KBr -+
1
I50
io
io0
0
PPM
Figure 2. (A) 25.16-MHz spectrum of 6 ; (B) 100-MHz spectrum of iceane (1); (C) 25.16-MHz spectrum (off-resonance of iceane (1).
Acknowledgment. We are grateful to the Research Corporation for support of this work. Chris A. Cupas,* Leonard Hodakowski Departmetit of Chemistry, Case Wester11 Reserce Utlicersity Clewlailrl, Ohio 44106 Receiced January 31, 1974
10
purification, with lithium aluminum hydride. l 3 This gave iceane, mp 327.0-328.5°.14 The pmr spectrum of iceane (Figure 2B) exhibited a singlet at 2.16 ppm for the bridgehead hydrogens and an AB quartet for the methylene hydrogens centered at 1.40 ppm with JAB = 12 Hz. In addition, the cmr spectrum was dramatic in that it showed but two singlets 6 31.80 and 28.86 ppm which split into a triplet and a doublet in the off-resonance cmr spectrum (Figure 2C). The mass spectrum of iceane was noteworthy in that only two other lines, other than the base peak (mje 162.2 amu), had relative intensities of greater than 2 0 x (m/e 79 [23 73 and 39 [34 %I amu). The chemistry of iceane (1) is under active investigation. (12) (a) Private communication, P. v , R . Schleyer and E. Engler, Princeton University. See also E. M. Engler, J. D. Andose, and P. v. R. Schleyer, J. Amer. Chem. SOC.,95, 8005 (1973); using Allinger's force field, the difference is virtually the same, 8.9 kcal,"ol. (b) N. L. Allinger, M. Tribble, M. A. Miller, and D. W. Wertz, ibid., 93, 1637 (1971). (13) C. W. Jefford, D. Kirkpatrick, and F. Delay, J . Amer. Chem. Soc., 94, 8905 (1972). (14) Melting points for all compounds were obtained using sealed capillaries. (15) The calculations by Schleyer and Engler also indicate that ethanoadamantane (iii) is the most stable tetracyclic Cn system. We have also confirmed this prediction. Reaction of iceane (1) with an AICh sludge catalyst gave ethanoadamantane (iii).
...
111
Ethanoadamantane. The Most Stable C12H18Isomer Sir. An astonishingly large number of tetracyclic C12H18 isomers are possible.' Of these, two have special appeal. 11, "iceane,"' is the first member of an isomeric, hexagonal diamond3 family with the Wurzite or ice structure. I, 2,4-ethanoadamantane (tetracyclo[6.3.1.02~6.05~1n]dodecane), like adamantane, was first discovered by Landa as a constituent from petroleum from H0donin.j As such diamondoid molecules probably arise in petroleum by rearrangement, this posed the possibility that I (and possibly I1 as well) might be prepared by Lewis acid-catalyzed isomerization, provided no other tetracyclic CIOHIB isomers are more stable.6 In fact, treatment of tetracycl0[6.4.0.0~~~?.0~~~]dodecane (111)7 with AIBr3 or with A1Br3-sludge catalyst in CS, at 0 or 25' gave ethanoadamantane (I)8 in 40-70x yields. Reaction times were as short as 30-60 min; with AIBr3, 90% of the product was I (glc). A careful study of this rearrangement by glc as a function of time (1) A computer program written by Professor W. T. Wipke reveals that 5291 tetracyclic ring systems with 12 skeletal carbon atoms are possible lnrivate communication'l. .~ ~~.~ . ~~. (2) L. F. Fieser, J . Chem: Eo'uc., 42, 408 (1965). (3) F. P. Bundy and J. S. Kasper, J . Chem. Phj,s., 46, 3437 (1967); R. E. Hanneman, H. M. Strong, and F. P. Bundy, Science, 155, 995 (1967). (4) C. A. Cupas and L. Hodakowski, J. Amer. Chem. Soc., 96, 4668 (1 9741, accompanying communication. ( 5 ) (a) S . HBla, S. Landa, and V. Hanui, Angew. Chem., 78, 1060 (1966); (b) Z. Weidenhaber and S. HAIa, Sb. YJ~s.Sk. Chem.-TechnoL Prague, Technol. Palic, D22, 5 (1971). (6) (a) R. C. Bingham and P. v. R. Schleyer, Fortschr. Chem. Forsch., 18, 1 (1971); (b) E. M. Engler and P. v. R. Schleyer, MTP ( M e d . Tech. Publ. Co.) Itit. Rec. Sci., Org. Chem., Ser. I , 5, 239 (1973). (7) (a) I . A. Akthar, G. I. Fray, and J. M. Yarrow, J. Chem. SOC.,812 (1968); (b) One of us (G. J. I
