Synthese, Struktur und Reaktionen Phenylethinyl‐substituierter Bicyclo[3.3.0]octane
Authors: Quast Helmut , Carlsen Jürgen , Röschert Horst , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von 
Published: July 2007

Syntheses, Structures, and Reactions of Phenylethynyl‐Substituted Bicyclo[3.3.0]octanes[1]

The bicyclo[3.3.0]octane‐3,7‐dione 5 adds phenylethynyl‐cerium(III) dichloride to afford an almost quantitative yield of the 3,7‐diols exo,exo‐, exo,endo‐, and endo,endo‐6 (1:2:2) which are separated by flash chromatography. While both exo,endo‐ and endo,endo‐6 are dehydrated by sulfuric acid in acetic acid to furnish the isomeric dienes C2‐ and Cs‐7, exo,exo‐6 rearranges to a bicyclic ketone (8), two tricyclic ketones (10a, b), and a tetracyclic ketone (12) as a consequence of the proximity of the endo‐phenylethynyl groups. The rearrangements of exo,exo‐6 are avoided when chlorotrimethylsilane is used as the dehydrating agent. Thus, a 90% yield of C2‐ and Cs‐7 is realized from the mixture of the 3,7‐diols 6. – The 2,6‐dione 13 reacts with phenylethynylcerium(III) dichloride to yield the hydroxyketone endo‐14 and the 2,6‐diols exo,endo‐ and endo,endo‐16 (1:1:3) which are separated by cyclic medium‐pressure liquid chromatography. Dehydration of endo‐14 furnishes the enone 15 which adds phenylethynylcerium(III) dichloride to afford the endo alcohol 17. Eventually, this is dehydrated to the diene 18. Formation of 18 from exo,endo‐16, and endo,endo‐16 as well, is accompanied by dehydrating cyclization to the oxanortwistane 19 (20%) readily separated from 18 by chromatography. – The encumbered diphenyldione 20 is converted into the highly substituted bicyclo[3.3.0]octa‐2,6‐diene 24 in 68% overall yield in a four‐step sequence involving additions of phenylethinyl‐cerium(III) dichloride (20→21 and 22→23) followed by dehydration of the endo alcohols 21 (→22) and 23 (→24). – In contrast to 20, the dicyanodiketone 25 adds phenylethynylcerium(III) dichloride at both carbonyl groups and, surprisingly, from the endo face, thus affording the exo,exo‐diol 26. At 150°C, 26 undergoes quantitatively an intramolecular dehydro Diels‐Alder reaction to yield the 1‐phenylnaphthalene derivative. 30. The lack of incorporation of deuterium from deuterated solvents attests to the intramolecular nature of the 1,5‐hydrogen shift converting the intermediate six‐membered cyclic cumulene 29 to the final product 30. – Dehydration of 26 produces the highly substituted bicyclo[3.3.0]octadiene‐2,6‐dicarbonitrile 27 which rearranges into an equilibrium mixture of the diastereomeric bisallenes exo,exo‐, exo,endo‐, and endo,endo‐28 on treatment with a strong base. In the same way, the identical mixture of diastereomers is obtained from each of the bisallenes 28 which had been separated by preparative medium‐pressure liquid chromatography. – The gross structures of all new compounds are based on spectroscopic evidence including IR, NMR, and mass spectra. The structures of endo,endo‐6, 12, exo‐14, endo,endo‐16 (α‐ and β‐form), 19, 24, 26 · 2 Me2SO, 27, exo,exo‐28, and endo,endo‐28 are established by X‐ray diffraction analyses. The preferred conformations of exo‐14, endo,endo‐16 (α‐ and β‐form), and 26 · 2 Me2SO in the crystalline state, as well as the stereochemistry of the nucleophilic attack to bicyclo[3.3.0]octanediones, and the mechanisms of the intramolecular reactions between the phenylethynyl groups are discussed.