Showing papers on "Dodecahedrane published in 1987"

Dodecahedrane aus [1.1.1.1]Pagodanen

Abstract: L'isomerisation, thermodynamiquement favorable, du pagodane en dodecahedrane peut etre accomplie a l'aide d'un metal catalyseur

Bissecododecahedraenes, Unusual Hyperstable Olefins

Abstract: 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.[31 The 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)"'4.51 for 2/3 (OS= I1.4/-.13.9 kcal/ mol). The diene 2 is of further structural interest because 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 A, however, is probably at least 0. l A 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 Synthesis of Organic Molecules with Polyhedral Symmetry

Abstract: Organic molecules with polyhedral symmetry have been and remain a challenge to organic chemists. Among hydrocarbons based on Platonic solids, cubane (Oh symmetry) was prepared by Eaton and Cole in 1964 and dodecahedrane, which exhibits the highest symmetry (Ih) ever imagined for any organic compound, was made by Paquette and co-workers in 1982. Tetrahedrane (Td symmetry), the “simplest” of the Platonic hydrocarbons, is unknown but the tetralithio and the tetra-tert-butyl derivatives were prepared in 1978 by the Schleyer group and the Maier group, respectively. Among molocules with chiral polyhedral symmetry (T, O, and I symmetry), the existence of molecules with conformational T symmety has been discussed by several workers. The first experimental proof of the existence of the conformational T symmetry molecule was given by Bartell and co-workers in 1970. The synthesis of the first optically active organic molecule with T symmetry has been accomplished by our group in 1982. As far as I know, organic molecule belonging to the O and I point group is still unknown.

The Synthesis of Organic Molecules with Polyhedral Symmetry

Abstract: Organic molecules with polyhedral symmetry have been and remain a challenge to organic chemists. Among hydrocarbons based on Platonic solids, cubane (Oh symmetry) was prepared by Eaton and Cole in 1964 and dodecahedrane, which exhibits the highest symmetry (Ih) ever imagined for any organic compound, was made by Paquette and co-workers in 1982. Tetrahedrane (Td symmetry), the “simplest” of the Platonic hydrocarbons, is unknown but the tetralithio and the tetra-tert-butyl derivatives were prepared in 1978 by the Schleyer group and the Maier group, respectively. Among molocules with chiral polyhedral symmetry (T, O, and I symmetry), the existence of molecules with conformational T symmety has been discussed by several workers. The first experimental proof of the existence of the conformational T symmetry molecule was given by Bartell and co-workers in 1970. The synthesis of the first optically active organic molecule with T symmetry has been accomplished by our group in 1982. As far as I know, organic molecule belonging to the O and I point group is still unknown.