The first example of a silver-manganese-rhenium cluster complex: heptacarbonyl-1kappa3C,2kappa4C-mu-dicyclohexylphosphido-1:2kappa2P-bis(triphenylphosphine)-1kappaP,3kappaP-triangulo-manganeserheniumsilver with disordered solvent.

The title compound, [ReMnAg(C(12)H(22)P)(C(18)H(15)P)(2)(CO)(7)], is the first crystallographically characterized silver-manganese-rhenium cluster. Due to intramolecular steric repulsion, the central AgMnRe(mu-P) ring deviates greatly from planarity. Metal-metal distances are Mn-Re 3.1712 (8), Ag-Mn 2.7367 (8) and Ag-Re 2.8485 (6) A.

Benzoannelated cis,cis,cis,trans-[5.5.5.6]fenestranes: syntheses, base lability, and flattened molecular structure of strained epimers of the all-cis series.

Tribenzofenestranes possessing the strained cis,cis,cis,trans-[5.5.5.6]-fenestrane skeleton have been synthesized from cis-2,6-diphenylspiro[cyclohexane-1,2'-indane]-1',3'-diols by two-fold cyclodehydration, in striking analogy to the strategy used previously to construct the stereoisomeric all-cis-tribenzo[5.5.5.6]fenestranes from the corresponding trans-diphenylspirodiols. In this manner, both of the parent hydrocarbons, all-cis-tribenzo[5.5.5.6]fenestrane 3 and cis,cis,cis,trans-tribenzo[5.5.5.6]fenestrane 4, have been made accessible from the spirodiketones 5 and 6, respectively. The C6-functionalized derivatives of 4-cis,cis,cis,trans-fenestranol 9 and cis,cis,cis,trans-fenestranone 12-were prepared through cis-diphenylspirotriol 8 and cis-diphenyldispiroacetaldiol 11, by using the same strategy. The cis,cis,cis,trans-[5.5.5.6]fenestrane framework readily epimerizes to the more stable all-cis isomers under basic conditions, but is stable under neutral or acidic conditions. For example, cis,cis,cis,trans-fenestranone 12 yielded all-cis fenestrane 3 under Wolff-Kishner conditions, but cis,cis,cis,trans-isomer 4 under Clemmensen conditions. Epimerization was also circumvented by radical-induced desulfurization of fenestrane dithiolane 15 with nBu3SnH/AIBN, producing 4 in excellent yields. A single-crystal X-ray structure analysis of 4 revealed that, in accordance with force field and semi-empirical MO calculations, the extra strain of the benzoannelated cis,cis,cis,trans-[5.5.5.6]fenestratriene framework [Estrain(4)-Estrain(3)=46 kJmol(-1)] is due both to the almost perfect boat conformation of the six-membered ring and to considerable bond angle widening at the central, non-bridged C4b-C15d-C11b unit (121 degrees). H/D exchange experiments with the cis,cis,cis,trans hydrocarbon 4 under basic conditions demonstrated that the strain-induced epimerization to 3 occurs through direct deprotonation of the "epimeric" benzylic bridgehead C7a-H bond, which was found to be more acidic than the two C-H bonds at the benzhydrylic bridgeheads.

A pseudo-trigonal bipyramidally coordinated Pt atom in dicarbonylbis(octacarbonyl-mu-dicyclohexylphosphidodirhenio)platinum(II).

In the title compound, [PtRe4(C12H22P)2(CO)18] or [(mu-PCy2)(CO)8Re2]2Pt(CO)2 (Cy is cyclohexyl), two phosphido-bridged dirhenium groups are linked by a Pt(CO)2 unit and show different bonding patterns for stereochemical reasons. The Re--Re distances are 3.2620 (15) and 3.0739 (15) A, and the Pt--Re distances are 2.9165 (12), 2.9025 (15) and 2.8548 (13) A.

Chiral auxiliary based approach toward the synthesis of C-glycosylated amino acids.

[reaction in text] In a chiral auxiliary based method C-glycosylated amino acids can be obtained by a 1,3-dipolar cycloaddition of a chiral glycine equivalent and C-1 allyl- or vinyl-derived carbohydrate building blocks as the key step. The products are formed regio- and diastereoselectively. Reductive cleavage of the N-O bond of the isoxazolidine and of the chiral auxiliary leads to C-glycosylated amino acids. The use of (-)-menthone to (+)-menthone as the auxiliary leads to the corresponding diastereomers.

Metabolites from fungi 15. New isocoumarins from an endophytic fungus isolated from the Canadian thistle Cirsium arvense.

One known (1) and five new polyketide metabolites (2-6) were isolated from the culture extract of an endophytic fungus, Mycelia sterila, from the Canadian thistle Cirsium arvense. Compounds 1-4 are members of the isocoumarin family, whereas metabolite 5 is a dihydrobenzofuran and 6 has an open chain structure. All compounds have an unusual methyl group at the aromatic ring that does not fit into the usual polyketide pattern.

Biomimetic synthesis of the racemic angucyclinones of the aquayamycin and WP 3688-2 types.

The first synthesis of the racemic 8-deoxy WP3688-2 angucycline antibiotic (3), with characteristic cis-hydroxy groups at C-4 a and C-12b, is reported. Key steps involve the coupling, mediated by samarium diiodide, of the bicyclic trione 37 to the tricyclic cis-diol 39. Biomimetic aldol cyclization of the corresponding dione 41 gave a mixture of the tetracyclic cis- and trans-3,4a-diols 42 and 43, which were oxidized by cerium ammonium nitrate to the quinones 45 and 3. The synthetic compounds 45 and 3 corresponded in configuration to the angucycline antibiotics aquayamicin (1) and WP 3688-2 (2), respectively.

Biologically active secondary metabolites from fungi. 12.(1) oidiolactones A-F, labdane diterpene derivatives isolated from oidiodendron truncata

Two known (1 and 2) and four new (3-6) diterpenes named oidiolactones A-F, respectively, and the antibiotic cladosporin were isolated from the fungus Oidiodendron truncata. The structure determination was mainly based on 1D and 2D NMR spectroscopy. The structures of compound 4, displaying an equilibrium between open-chain and cyclized form, and of cladosporin were confirmed by X-ray analysis.

Dihydroisocoumarins from fungi: isolation, structure elucidation, circular dichroism and biological activity.

Five known and three new dihydroisocoumarins were isolated from different fungi. The new isocoumarins are 5-chloro-6-hydroxymellein, 5-chloro-4,6-dihydroxymellein and 5,6-dihydroxymellein. The absolute configuration of these secondary metabolites was confirmed by CD measurements and in two cases by X-ray structure analysis.

A Triangular Iron(III) Complex Potentially Relevant to Iron(III)-Binding Sites in Ferreascidin.

An asymmetric triangular Fe(III) complex has been synthesized by an unusual Fe(II) -promoted activation of salicylaldoxime. Formation of the ligand 2-(bis(salicylideneamino)methyl)phenol in situ is believed to occur through the reductive deoximation of salicylaldoxime by ferrous ions. The trinuclear ferric complex has been characterized on the basis of elemental analysis, IR, variable-temperature magnetic susceptibility, and EPR and Mössbauer spectroscopies. The molecular structure established by X-ray diffraction consists of a trinuclear structure with a [Fe3 (µ3 -O)(µ2 -OPh)](6+) core. Two iron ions are in a distorted octahedral environment having FeN2 O4 coordination spheres, and the five-coordinated third iron ion, with an FeNO4 coordination sphere, is in a trigonal bipyramidal environment. The magnetic susceptibility measurements revealed an St = 5/2 ground state with the antiparallel exchange interactions J = - 34.3 cm(-1) , J' = - 4.7 cm(-1) , and D = - 0.90 cm(-1) . The EPR results are consistent with a ground state of S = 5/2 together with a negative D5/2 value. The Mössbauer isomer shifts together with the quadrupole splitting also provide evidence for the high-spin state of the three ferric sites. Magnetic Mössbauer spectra lead to the conclusion that the internal magnetic fields possibly lie in the plane of the three ferric ions.