Burkhard Knieriem

Palladium-catalyzed domino coupling reactions of aryl halides with norbornene and norbornene derivatives : a simple route to polycyclic aromatic compounds

Under palladium-catalysis, norbornene 1, dicyclopentadiene 10, norbornenol 13, and norbornenone 15 react with unsubstituted as well as substituted bromo- and iodobenzenes to give 1 : 3 coupling products with 4-aryl-9,10-dihydrophenanthrene units with up to 70% isolated yields. The structures of two such products 4a and 4e were proved by X-ray crystal structure analysis. 2-Bromothiophene 17 reacts with 1 and 10 to yield a mixture of 2 : 1 and 3 : 1 coupling products, while 3-iodopyridine 22a, 3-iodo-6-methylpyridine 22b and 4-iodopyridine 25 give only 2 : 1 coupling products with 5,6-dihydro-3,8-phenanthroline and 5,6-dihydro-2,9-phenanthroline units, respectively. Some new mechanistic insights into this interesting four-component domino coupling reaction are presented. The products can easily be transformed by photocyclization/dehydrogenation and/or flash vacuum pyrolysis to a variety of cyclopentadiene-anellated polycyclic aromatic compounds in very high yields. The reported sequence also presents the easiest access to benzo[e]pyrene.

Palladium-Catalyzed Self-Cross Coupling of o-Bromo-trans-stilbenes To Yield 9,10-Bis(arylmethylene)-9,10-dihydroanthracenes©

Under Palladium catalysis [Pd(OAc)2, K2CO3, LiCl, Bu4NBr, DMF] o-bromo-trans-stilbene (trans-7a) reacts to give 9,10-dibenzylidene-9,10-dihydroanthracene (4a) with formation of a new six-membered ring. The (Z) diastereomer crystallizes preferentially to give pure (Z)-4a, as proved by X-ray crystal structure analysis. A variety of substituted o-bromostilbenes and heterocyclic analogs 7 were prepared by Wittig olefination of o-bromobenzaldehyde with substituted benzyltriphenylphosphonium ylides, Wittig-Horner-Emmons olefination of arenecarbaldehydes with diethyl o-bromobenzylphosphonate or Wittig olefination of substituted benzaldehydes with substituted (o-bromobenzyl)-diphenylphosphonium ylides, respectively. The cis-o-bromostilbenes were photoisomerized to the trans diastereoisomers trans-7 by irradiation in the presence of diphenyl disulfide. All of these o-bromo-trans-stilbenes trans-7a–g and trans-7j, k under palladium catalysis reacted to the corresponding 9,10-bis(arylmethylene)-9,10-dihydroanthracenes 4, mostly as mixtures of (E) and (Z) diastereomers (50-97 % yield). The (Z) diastereomer of the parent 4a and the alkyl-substituted compounds 4c and 4e could be purified by simple crystallization, and in some runs, only (Z)-4a, c, e were obtained. Among the heterocyclic analogs trans-7h, i only the furyl derivative trans-7h reacted (76 % yield) cleanly, whereas the pyridine analog trans-7i gave a mixture of products from which the rather sensitive product 4i could not be isolated in pure form. The cis-o-bromostilbenes cis-7a, c cyclized to phenanthrenes under the same conditions (70-71 % yield). The UV spectra of compounds 4a, c–k are similar to that of anthracene, and so are the oxidation and reduction potentials of (Z)-4a.

Carboncarbon and carbonchalcogen spinspin coupling constants in chalcogen-substituted acetylenes

Abstract CarbonCarbon and carbonchalcogen spinspin coupling constants have been determined for chalcogen-substituted phenyl-, alkyl- and silyl-acetylenes. The changes in the CC couplings involving acetylenic sp carbons are explained in terms of the electronegativities of the substituent. The chalcogen-carbon coupling dependence on carbon hybridization previously noted for tellurium derivatives is confirmed.

Highly Substituted Spiro[4.4]nonatrienes from a -Amino-Substituted ,-Unsaturated Fischer Carbene Complex and Three Molecules of an Arylalkyne

A novel mode of reaction towards arylethynes is shown by the β-trimethylsilyl-substituted α,β-unsaturated Fischer carbene complexes 1. A mixture of the isomeric, highly substituted spiro[4.4]nonatrienes 2 and 3 is formed by the formal insertion of three alkyne molecules and subsequent cyclization (see scheme). Such selective triple insertions of alkynes into ethenylcarbene complexes have not been previously observed.

Indo calculations of J(CC) and J(CSI) in silyl derivatives of acetylene and diacetylene

Abstract INDO FPT calculations of the carbon—carbon and carbon—silicon spin—spin coupling constants have been performed for silyl substituted acetylenes and diacetylene. The calculated values are compared with available experimental data. The roles of the various contributions to J(CC) are discussed.

Hochsubstituierte Spiro[4.4]nonatriene aus einem β‐aminosubstituierten α,β‐ungesättigten Fischer‐Carbenkomplex und drei Molekülen eines Arylalkins

Einen neuartigen Reaktionsmodus gegenuber Arylethinen zeigt der β-trimethylsilylsubstituierte, α,β-ungesattigte Fischer-Carbenkomplex 1: Durch Insertion von drei Alkin-Molekulen und nachfolgende Cyclisierung entsteht ein Gemisch der isomeren hochsubstituierten Spiro[4.4]nonatriene 2 und 3 (siehe Schema). Derartige selektive Dreifachinsertionen von Alkinen in Ethenylcarbenkomplexe wurden bisher noch nicht beobachtet.