Synthesis of the fungus metabolite cladosin C.

Cladosin C is one of the few known enaminotetramic acids, isolated from extracts of the deep sea fungus Cladosporium sphaerospermum. It was synthesised in ten steps and 14% overall yield by a late-stage amination of the corresponding 3-acyltetramic acid. This was obtained by a Dieckmann condensation of an N-ß-ketoacylaminoester derived from dehydrovalinate and the thioester-terminated side chain containing the stereogenic centre which stemmed from poly-(R)-3-hydroxybutyrate.

Enantioselective synthesis of putative lipiarmycin aglycon related to fidaxomicin/tiacumicin†B.

An enantioselective synthesis of a putative lipiarmycin aglycon was accomplished and features: 1) Brown's enantioselective alkoxyallylboration and allylation of aldehydes, 2) chain elongation by iterative Horner-Wadsworth-Emmons olefination, 3) Evans' aldol reaction and 4) an ene-diene ring-closing metathesis. A neighboring-group-assisted chemoselective reductive desilylation was uncovered in this study and was instrumental to the realization of the present synthesis.

Diastereodivergent behavior of alkyl versus cyano allenylcuprates toward aldehydes: a key role for lithium.

The stereodivergent behavior of allenyl(cyano)- and allenyl(alkyl)cuprates toward aldehydes, providing a selective preparation of both syn- and anti-homopropargylic alcohols, is described. This study, which combines both experimental and theoretical support, shows that the copper nontransferred "dummy ligand" controls the localization of the lithium cation with respect to the allenylcuprate moiety. As a consequence, Li(+) acts as a Lewis acid activator but also controls the diastereoselectivity during the addition of allenylcuprates onto aldehydes. The combined high selectivity, efficiency, and versatility of these cuprate compounds opens the way to new one-pot synthetic procedures, as illustrated by the combined Klein rearrangement/transmetalation methodology described herein.

Lewis acid/CpRu dual catalysis in the enantioselective decarboxylative allylation of ketone enolates.

The addition of a Lewis acidic metal triflate salt Mg(OTf)(2) as co-catalyst in the CpRu-catalyzed decarboxylative allylation of in situ-generated ketone enolates allows the reaction to proceed at lower temperature with higher regio- and enantioselectivity. Even so-far-unreactive substrates react.

Self-adaptable catalysts: substrate-dependent ligand configuration.

Pd(II) allyl and Pd(0) olefin complexes containing the configurationally labile ligand 1,2-bis-[4,5-dihydro-3H-dibenzo[c-e]azepino]ethane were studied as models for intermediates in Pd-catalyzed allylic alkylations. According to NMR and DFT studies, the ligand prefers C(s) conformation in both eta3-1,3-diphenylpropenyl and eta3-cyclohexenyl Pd(II) complexes, whereas in Pd(0) olefin complexes it adopts different conformations in complexes derived from the two types of allyl systems in both solution and, as verified by X-ray crystallography, in the solid state. These results demonstrate that the Pd complex is capable of adapting its structure to the reacting substrate. The different structural preferences also provide an explanation for the behavior of 1,3-diphenyl-2-propenyl acetate and 2-cyclohexenyl acetate in Pd-catalyzed allylic alkylations using pseudo-C2 and pseudo-C(s) symmetric ligands.

Chiral or not chiral? A case study of the hexanuclear metalloprisms [Cp(6)M(6)(micro(3)-tpt-kappaN)(2)(micro-C2O4-kappaO)(3)]6+ (M = Rh, Ir, tpt = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine).

Cationic hexarhodium and hexairidium complexes with a trigonal prismatic architecture have been synthesised in good yield by self-assembly of the dinuclear oxalato-bridged complexes [Cp(2)M(2)(micro-C(2)O(4)-kappaO)Cl(2)] (M = Rh; 1: Ir; 2) with 2,4,6-tri(pyridine-4-yl)-1,3,5-triazine (tpt) in the presence of AgO(3)SCF(3). The trigonal prismatic cations [Cp(6)Rh(6)(micro(3)-tpt-kappaN)(2)(micro-C(2)O(4)-kappaO)(3)](6+) (3) and [Cp(6)Ir(6)(micro(3)-tpt-kappaN)(2)(micro-C(2)O(4)-kappaO)(3)](6+) (4) have been isolated as their triflate salts. The single-crystal X-ray structure analysis of [3][O(3)SCF(3)](6) shows two enantiomers in the racemic crystal (space group C2/c), the chirality being due to a twist of the two tpt units. By contrast, the single-crystal X-ray structure analysis of [4][O(3)SCF(3)](6) shows a perfectly eclipsed conformation of the tpt units, so that is not chiral in the crystal state (space group Fd3[combining macron]c). However, in solution, enantiodifferentiation in the presence of the chiral anion Delta-BINPHAT is observed by (1)H NMR spectrometry not only in the case of 3, but also in the case of 4. This suggests that the iridium derivative 4, which is not chiral in the solid state, adopts chiral conformations in solution.

Hexacoordinated phosphates: how to teach old chiral anions new asymmetric tricks.

Chemical reactions and processes often involve chiral, yet racemic, cationic reagents, intermediates, or products. To afford instead nonracemic or enantiopure compounds, an asymmetric ion pairing of the cations with enantiopure anions can be considered--the counter ions behaving as asymmetric auxiliaries, ligands, or reagents. Detailed herein is a short review of our approach toward gaining reliable and predictable control over stereoselective ion pairing phenomena through the synthesis and use of novel configurationally stable hexacoordinated phosphate anions.

Self-assembled hexanuclear arene ruthenium metallo-prisms with unexpected double helical chirality.

Self-assembly of 2,4,6-tripyridyl-1,3,5-triazine (tpt) subunits with arene ruthenium building blocks and oxalato bridges affords cationic triangular metallo-prisms of the type [Ru6(arene)6(tpt)2(C2O4)3]6+ (arene = C6Me6 and p-Pr(i)C6H4Me); the unexpected double helical chirality of the metallo-prisms observed in the solid state persists in solution giving rise to two different stereodynamic processes as demonstrated by NMR enantiodifferentiation experiments.