The Thermal Isomerizations of Bicyclo[2.1.0]pent-5-yl Methyl Ketones: endo-exo stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketones

Bicyclo[2.1.0]pent-5-yl methyl ketones undergo two thermal isomerization reactions. The endo-exo stereomutation follows the ring-flip path in better than 90%, with inversion of the configuration of the angular carbon atoms by cleavage and reclosure of the central bond. Stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketone do not involve a common intermediate and proceed on separate potential energy surfaces. The activation parameters of the rearrangement suggest an allowed concerted cycloreversion process.     

Synthesis of bisbenzannulated spiroketals-model studies for a modular approach to rubromycins

[reaction: see text] A highly flexible synthesis of bisbenzannulated spiroketals is described with additions of lithiated methoxyallene to aryl aldehydes and Heck reactions as key steps. Subsequent hydrogenations and ketalizations afforded the desired spiroketals in good yields and with predominating trans-configuration. With model compound 30, already bearing the fully substituted naphthyl core of rubromycins, the ketalization proceeded efficiently providing the expected product 31 and the isopropoxy compound 32. Both products are advanced model compounds of heliquinomycin.     

A family of ferro- and antiferromagnetically coupled decametallic chromium(III) wheels

The synthesis and crystal structures of a family of decametallic Cr(III) "molecular wheels" are reported, namely [Cr10(OR)20(O2CR')10] [R' = Me, R = Me (1), Et (2); R' = Et, R = Me (3), Et (4); R' = CMe3, R = Me (5), Et (6)]. Magnetic studies on 1-6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R') the nearest neighbour CrCr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R = Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S = 0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S = 15 ground state expected for ferromagnetic coupling of ten Cr(III) ions, and they also indicate that a single J-value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1-6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J = 0, hence changing the sign of J.     

Isolation and structure elucidation of two new cytotoxic metabolites from red yeast rice

In this study, 10 already described secondary metabolites and 2 unknown metabolites were identified in an extract of Monascus purpureus by high-performance liquid chromatography-diode array detection. The unknown metabolites were isolated and their chemical structures were elucidated. The new metabolites possess the molecular formulas C(21)H(27)NO(4) and C(23)H(31)NO(4). They were named monascopyridines E and F due to their pyridine backbone. The cytotoxicity of the new compounds was studied using immortalised human kidney epithelial cells displaying IC(50) values in the micromolar range.