Synthesis of Halochromates with Inorganic Stable Complex Cations: New,Mild and Efficient Oxidants

The halochromates of general formulas of [M(en) ₃ ][XCrO ₃ ] ₃ (X = Cl,F; M = Co,Cr) and [Co(NH ₃ ) ₆ ][XCrO ₃ ] ₃ (X = Cl,F) were prepared and characterized by IR spectroscopy and elemental analysis. These oxidants were examined for oxidizing some alcohols to their aldehydes and ketones and their oxidizing ability was compared with other relevant oxidants.     

Synthesis of functionalised cyclohexadienes through addition of lithiated phosphine borane complexes to benzonitriles

Functionalised 1,3- and 1,4-cyclohexadienes have been prepared through dearomatisation of benzonitriles by sequential conjugate addition of -lithium alkyl(diphenyl)phosphine borane in the presence of HMPA and capture of the intermediate anion with protonating and alkylating reagents.     

Conversions of hydrocarbons treated with neodymium metal under the conditions of mechanochemical activation at room temperature

The conversions of cyclohexene and 1,3- and 1,4-cyclohexadiencs treated with neodymium metal under the conditions of mechanochemical activation at 20 °C have been studied. A complicated cycle of conversions, including isomerization, disproportionation, and polymerization, occurs under the reaction conditions. A mechanism for the conversion of the hydrocarbons involving organornetallic intermediates is proposed.The conversion of hexane under the conditions used for the reactions with cyclohexene and cyclohexadienes varies only slightly, which makes it possible to use hexane as the internal standard.Deceased.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1386–1390, June, 1996.     

Importance of steric factors in face-selective cycloadditions: 1,6-annulated cyclohexa-1,3-dienes

Diastereotopically nonequivalent π-facial 1,6-annulated-1,3-cyclohexadienes have been explored as probe molecules to assess the face-selectivities in cycloadditions. Steric factors have been found to be important in controlling the face-selectivities with these dienes. Studies with the hitherto unexplored diene 5 were also consistent with the order C-H > C-C for hyperconjugative stabilization of the transition state.     

Stereoselective synthesis of (+)-nephrosteranic acid, (+)-trans-cognac lactone, and (+)-trans-whisky lactone using a chiral cyclohexadienyl Ti compound

We present the stereoselective transfer of cyclohexadienyl from 3-metalated 1,4-cyclohexadienes to various aldehydes. Lewis-acid-mediated "allylation" of aldehydes by treatment with 3-silylated and 3-stannylated 1,4-cyclohexadienes could not be achieved with high diastereoselectivity. In contrast, cyclohexadienyl titanium compounds reacted with both aliphatic and aromatic aldehydes with good-to-excellent diastereoselectivities. Reaction of a chiral TADDOL-derived (TADDOL, 2,2-dimethyl-alpha,alpha,alpha',alpha'-tetraphenyl-1,3-dioxolandimethanol) cyclohexadienyl Ti derivative with various aldehydes led to the corresponding homoallylic alcohols with excellent diastereo- and enantioselectivities. Lower selectivities were obtained with chiral B-cyclohexadienyldiisopinocampheylborane. The 1,3-cyclohexadienes are very useful building blocks for the preparation of biologically important gamma-butyrolactones. Short efficient syntheses of (+)-nephrosteranic acid, (+)-trans-whisky lactone, and (+)-trans-cognac lactone by desymmetrization of 1,4-cyclohexadiene are described.     

1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

1,4‐Cyclohexadiene derivatives are easily accessed via transition‐metal cycloadditions of 1,3‐dienes with alkynes. The mild reaction conditions of several transition‐metal‐catalysed reactions allows the incorporation of various functional groups to access functionalised 1,4‐cyclohexadienes. The control of the regiochemistry in the intermolecular cobalt‐catalysed Diels–Alder reaction is realised utilising different ligand designs. The functionalised 1,4‐cyclohexadiene derivatives are valuable building blocks in follow‐up transformations. Finally, the oxidation of the 1,4‐cyclohexadienes can be accomplished under mild conditions to generate the corresponding arene derivatives.     

Valuable New Cyclohexadiene Building Blocks from Cationic η5‐Iron–Carbonyl Complexes Derived from a Microbial Arene Oxidation Product

Biooxidation of benzoic acid by Ralstonia eutropha B9 provides an unusual cyclohexadiene carboxy diol that contains a quaternary stereocentre. Tricarbonyliron derivatives of this chiron, on treatment with acid, give two isomeric η⁵‐cyclohexadienyl complexes as observed by NMR spectroscopy. Both of these can be subjected to the addition of nucleophiles to provide isomeric cyclohexadiene complexes with new substituent patterns, several of which have been characterised crystallographically. De‐metallation of these provides a versatile library of cyclohexadiene building blocks, the utility of which is demonstrated by formal syntheses of oseltamivir. The mechanism of product formation and its stereochemical implications are discussed, as are the procedures undertaken to establish the enantiopurity of a representative cyclohexadiene product.     

Recent advances in "formal" ruthenium-catalyzed [2+2+2] cycloaddition reactions of diynes to alkenes

"Formal" and standard RuII-catalyzed [2+2+2] cycloaddition of 1,6-diynes to alkenes gave bicyclic 1,3-cyclohexadienes in relatively good yields. When terminal 1,6-diynes 1 were used, two isomeric bicyclic 1,3-cyclohexadienes 4 or 6 were obtained, depending on the acyclic or cyclic nature of the alkene partner. When unsymmetrical substituted 1,6-diynes 7 were used, the reaction with acyclic alkenes took place regio- and stereoselectively to afford bicyclic 1,3-cyclohexadienes 8. A cascade process that behaves as a "formal" RuII-catalyzed [2+2+2] cycloaddition explained these results. Initially, a Ru-catalyzed linear coupling of 1,6-diynes 1 and 7 with acyclic alkenes occurs to give open 1,3,5-trienes of type 3, which after a thermal disrotatory 6e(-) pi-electrocyclization led to the final 1,3-cyclohexadienes 4 and 8. When disubstituted 1,6-diyne 10 was used with electron-deficient alkenes, new exo-methylene cyclohexadienes 12 arose from a competitive reaction pathway.