Up to seven-component adducts by unprecedented multiple alkyne and carbonyl insertions in the metal-carbon bond of chromium alkoxy alkynyl carbene complexes

Chromium alkoxy alkynyl Fischer carbene complexes react with symmetrical internal alkynes to form new and different organometallic species, which result from consecutive insertions of several alkyne units and carbonyl groups into the metal-carbon bond. The insertion sequence can be controlled and, by slight modification of the reaction conditions, it can be directed to the preparation of either seven- or five-component adducts. Three molecules of alkyne, two carbonyl groups, the carbene ligand and the chromium metal moiety partake in the creation of seven new carbon-carbon bonds and two five-membered carbocycles in the first case while four new carbon-carbon bonds, a sigma Cr--C(sp(2)) bond and a cyclopentadienyl moiety are built in the second case. Evidence that five-component chromium complexes are intermediates in the formation of seven-component adducts is provided; they are also able to insert a unit of a different internal alkyne which confers more diversity to the seven-component adducts. The presence of the sigma Cr--C(sp(2)) bond has also been exploited to develop the synthesis of both cyclopentene-fused and novel spiro-cyclopentenones as well as symmetrical biscyclopentenones. Finally, the isolation of six-component adducts, when tolane was employed as the initial alkyne, provides further support to the proposed mechanism.     

Design and synthesis of novel polyheterofunctionalyzed cyclopentenones

Novel highly functionalized chlorocyclopentenones derivatives with N-, O-, and C-substituents were synthesized.     

Solvent and substituent effects on the photochemistry of norbornadiene-diarylacetylene Pauson-Khand adducts

The photochemistry of Pauson-Khand cycloadducts of norbornadiene with a series of bis-aryl alkynes has been studied. Two types of photochemical transformation take place: photorearrangement to tricyclic ketones or photochemical 6π electrocyclization. High selectivity levels have been attained for each pathway, controlled by the polarity of the solvent, irradiation wavelength, and presence (or absence) of oxygen.     

Efficient synthesis of [H2]-tetrahydrodicranenone B and a 3-oxa-analogue resistant against β-oxidation

A short efficient synthesis of two analogues of tetrahydrodicranenone B as well as a formal synthesis of tetrahydrodicranenone B (1) itself has been devised. The approach is based on an addition/elimination sequence of in situ prepared organocuprates to the iodocyclopentenone (9). The procedure is compatible with functionalised substituents.     

Palladium-catalyzed tandem oxidative cyclization of 1-bromohexa-1,5-dien-3-ols: easy access to cyclopentenones

The novel Pd-catalyzed tandem cyclization of 1-bromohexa-1,5-dien-3-ols, prepared from the corresponding β-bromo-vinylaldehydes to cyclopentenone derivatives has been developed.     

Analysis of fungal cyclopentenone derivatives from Hygrophorus spp. by liquid chromatography/electrospray-tandem mass spectrometry

Fruitbodies of the genus Hygrophorus (Basidiomycetes) contain a series of anti-biologically active compounds. These substances named hygrophorones possess a cyclopentenone skeleton. LC/ESI-MS/MS presents a valuable tool for the identification of such compounds. The mass spectral behaviour of typical selected members of this group under positive and negative ion electrospray conditions is discussed. Using the ESI collision-induced dissociation (CID) mass spectra of the [M + H]+ and [M - H]- ions, respectively, the compounds can be classified with respect to the substitution pattern at the cyclopentenone ring and the type of oxygenation at C-6 (hydroxy/acetoxy or oxo function) of the side chain. The elemental composition of the fragment ions was determined by ESI-QqTOF measurements. Thus, in case of the negative ion CID mass spectra an unusual loss of CO2 from the deprotonated molecular ions could be observed.     

Vinyl sulfoxides as stereochemical controllers in intermolecular Pauson-Khand reactions: applications to the enantioselective synthesis of natural cyclopentanoids

The use of sulfoxides as chiral auxiliaries in asymmetric intermolecular Pauson-Khand reactions is described. After screening a wide variety of substituents on the sulfur atom in alpha,beta-unsaturated sulfoxides, the readily available o-(N,N-dimethylamino)phenyl vinyl sulfoxide (1 i) has proved to be highly reactive with substituted terminal alkynes under N-oxide-promoted conditions (CH3CN, 0 degrees C). In addition, these Pauson-Khand reactions occurred with complete regioselectivity and very high diastereoselectivity (de=86->96 %, (S,R(S)) diastereomer). Experimental studies suggest that the high reactivity exhibited by the vinyl sulfoxide 1 i relies on the ability of the amine group to act as a soft ligand on the alkyne dicobalt complex prior to the generation of the cobaltacycle intermediate. On the other hand, both theoretical and experimental studies show that the high stereoselectivity of the process is due to the easy thermodynamic epimerization at the C5 center in the resulting 5-sulfinyl-2-cyclopentenone adducts. When it is taken into account that the known asymmetric intermolecular Pauson-Khand reactions are limited to the use of highly reactive bicyclic alkenes, mainly norbornene and norbornadiene, this novel procedure constitutes the first asymmetric version with unstrained acyclic alkenes. As a demonstration of the synthetic interest of this sulfoxide-based methodology in the enantioselective preparation of stereochemically complex cyclopentanoids, we have developed very short and efficient syntheses of the antibiotic (-)-pentenomycin I and the (-)-aminocyclopentitol moiety of a hopane triterpenoid.