Bissecododecahedraenes, Unusual Hyperstable Olefins

Bissecododecahedraenes, Unusual Hyperstable Olefins** By Paul R . Spurr, Bulusu A. R . C. Murty, Wolf-Dieter Fessner, Hans Fritz, and Horst Prinzbuch * As an alternative to the catalytic procedure,"' directed multistep pagodane-dodecahedrane transformations (routes A and/or B/C in Ref. [2]) are a current goal: for example, via the intermediates 2-5 (Fig. 1) in the case of the basic skeletons 116. At intermediate 5 , this route converges with Puquette's dodecahedrane synthesis, which was recently considerably improved for step 5 - 6 , which involves dehydrogenation and simultaneous C-C bond formation.[31The calculated (MM2)I4] molecular structures (Fig. I ) clearly reveal how, with iTcreasing expansion of the "waist" of 1 (1.55 A) to 3.49 A in 4, the distance between the opposing methylene C atoms (which are eventually to undergo direct C-C bond formation) and their syn hydrogen atoms becomes increasingly small. The enthalpies of formation, AH?, decrease continuously on going from 1 to the "stabilomer"[sl 6 , while the strain energies, E,,,, decrease discontinuously (Fig. 1). The increase of E,,, in going from 2 via 3 to 4, which is primarily a consequence of the increasing transannular and vicinal H / H interactions, necessarily implies considerably reduced "olefinic strain (OS)"'4.51for 2/3 (OS= - I1.4/-.13.9 kcal/ mol). The diene 2 is of further structural interest because

Fig. I . L.nthalpies of formation. AH? (-).

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A,

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and strain energies, E,,, (----), of 1-6 in kcal/mol. Distances [A]

Prof. Dr. H. Prinzbach, Dr. P. R. Spurr, Dr. Bulusu A. R. C. Murty, Dr. W.-D Fessner, Prof. Dr. H. Fritz Chemisches Labordtoriurn der Universitat, lnstitut fur Organische Chemie und Biochemie Albrrtstrasse 2 I , D-7800 Fretburg (FRG) This work was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and BASF AG. f. R . S.and B . A . R. C. M . thank the Alexander von Humboldt Foundation for a fellowship.

Angew Clwm In,. Ed. Engl. 26 11987) No. 5

the C = C bonds, held in an overall very rigid molecular skeleton, have an unusually small transannular distance, with ideal colinear orientation of the n orbita1s;'"l the calculated value of 2.62 however, is probably at least 0. l too The (transannular) strain inherent in 2 and 3 is manifested in a pyramidalization of the olefinic centers by about 10" and So, respectively. Comparable energetic and structural relationships were calculated for the reaction sequence starting from the diketone 7 and proceeding via the intermediates 10-12. After initial model studies,"] a preparatively efficient entry into the reaction sequence 1 + 6 was made possible by the finding that [l.l.l.l]pagodane 1 reacts with bromine (in very large excess) regiospecifically and quantitatively to give the crystalline, moisture-sensitive dibromide 8 (m.p. = 240-241 "C (dec.)); the reaction occurs thermally within days and upon irradiation (300-W Osram Vitalux lamp, pyrex filter) within minutes. Under standard conditions (Zn, dimethylformamide, 160°C, 3 h), 8 is converted in high yield (89%) into the crystalline bissecododecahedradiene 2 (m.p. =260°C (dec.)), which, especially in solution, is sensitive toward oxidation. Analogously, the pagodanedione 7 is transformed, via the dibromide 9 (m.p. =294-29S°C (dec.), loo%), into the dienedione 10 (m.p. = 322-323 "C, 85%)."I Heating or irradiation of the dibromides 8/9 results in loss of bromine with re-formation of 117 ; this finding explains why a large excess of reagent is necessary in their preparation.

The unique orientation of the C-C double-bond n orbitals in the bissecododecahedradiene skeleton of 2 and 10 gives rise, according to PE spectroscopic analysis, to an unusually strong through-space n,n homoconjugation (ca. 2 eV)/'ol which is presumably also responsible for the relatively long-wavelength uv absorption Of A d 7 0 (sh, 180)), 250 nm (sh, ~ = 4 5 0 )and 10 (CH,CN, A=320 nm (sh, E = 1 IS), 280 (sh, 170), 250 (190)). Acetone-

0 V C H Verlagsge.~ellscliajimbH, 0-6940 Wernheim. 1987

0570-0833/87/0505-0455 $ 02.50/0

455

sensitized excitation of 2 and 10 results in rapid cycloaddition to give 1 and 7, re~pectively.~"] Bromine adds regiospecifically to give 8 and 9.

77

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obtain 19a,b and 20a,b, respectively, thereby allowing further functionalization of the molecular skeleton by reactions at the remaining C = C bond. For 15b/16b,the quantitative C-H insertion of chlorocarbene (to give 17b/ 18b), obtained with an excess of reagent, is so slow that 15b/16b can be selectively prepared.

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17

Received: January 19, 1987 [Z 2054 I€] German version: Anyew. Clrem. 99 (1987) 486

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13114)

The predicted hyperstability of 2 and 3 has adverse consequences for our approach. Reaction of the dienes 2 and 10 with diimine, which has proved useful for the reduction of highly substituted olefins, only results in hydrogenation to the monoenes 3 and 11, respectively; not even trace amounts ( < I%), even under forced conditions, of the tetrahydro derivatives can be detected. The greater reactivity of the dienes 2/10 compared with the enes 3/11 presumably reflects a partial compensation of the hyperstability by the destabilizing transannular n/n repulsion. Diverse noble metal catalysts (Pd, Pt, Rh) were also unable to effect the hydrogenations 3-4 and 11-12; under the drastic conditions that are already necessary for steric reasons, varying amounts of 1 and 13,in addition to 3,are formed from 2. Compounds 13 and 14, respectively, are formed in nearly quantitative yields upon short heating of the enes 3 and 11 to 300"C, which demonstrates the efficient transannular stabilization of the intermediate homoallyl radical (or cation) and an efficient competition with the catalytic route.{'] As observed in similar cases, the hyperstability of the enes 3/11 can be overcome by the use of reagents having greater "driving force." They are oxidized quantitatively to the epoxides 15a/16a with m-chloroperbenzoic acid (CHCI,, NaOAc, 20°C); under these conditions, the dienes 2/10 are oxidized to the epoxides 19a/20a and the diepoxides 21a/22a.f"1 Under phase-transfer conditions, dichlorocarbene also adds to 3/11 (to give 15b/16b)and to 2/10 (to give 19b/20b and 21b/22b). In these reactions, the second addition is usually so much slower that it is possible to 456

0 V C H Verlagcgesellschafr m b H . D-6940 Weinheim. 1987

[I] W.-D. Fessner, Bulusu A R. C . Murty, J. Worth, D. Hunkler, H. Fritz, H. Prinzbach, W. D. Roth, P. yon R Schleyer, A B McEwen, W. F. Maier, Angew. Chem 99 (1987) 484: Angen. Chem. Int. Ed. Engl. 26 (1987) 452. (21 W -D. Fessner, Bulusu A. R. C. Mtirty. H. Prinzbach, Anyew Chem. 99 (1987) 482; Angew. Chem. Inr. Ed. Engl. 26 (1987) 451. 131 L. A. Paquette, Y . Miyahard, C . W Doecke, J A m . Chem Soc. 108 (1986) 1716. [4] W:D. Fessner, Dis.rer/ation. Universitst Freiburg 1986. 151 W. F. Maier, P. von R. Schleyer, J. A m . Chem. Soc. 103 (1981) 1891; A. B. McEwen, P. von R. Schleyer, rhtd. 108 (1986) 3951. [6] Cf. K. B. Wiberg, M. G. Matrurro, P. J. Okarma, M. E. Jason, J . A m Chem SOC.106 (1984) 2 194. 171 0 . Ermer, C.-D. Bodecker, H. Preut. Angew. Chem. 96 (1984) 57; Angew Chem In!. Ed. Engl. 23 (1984) 55. [X] G Sedelmeier. W.-D. Fessner, R. Pinkos, C. Grund, Bulusu A. R. C. Murty, D. Hunkler, G Rihs, H. Fritz, C. Kriiger, H. Prinzbach, Chem. Eer. 119 (1986) 3442. [9] The new compounds were characterized by their spectra ( ' H - N M R , "CN M R , IR, MS) a n d by elemental analyses. For example. Z ( n o n a c y ~ clo112,6~o~o?."~o'.l v~07."'.ol