A novel undecametallic iron(III) cluster with an S = (11)/(2) spin ground state

The reaction of [NEt(4)](2)[Fe(2)OCl(6)] with sodium benzoate, 4,6-dimethyl-2-hydroxypyrimidine (dmhp), and 1,1,1-tris(hydroxymethyl)ethane (H(3)thme) gives the undecametallic compound [NEt(4)][Fe(11)O(4)(O(2)CPh)(10)(thme)(4)(dmhp)(2)Cl(4)]. X-ray crystallography, EPR spectroscopy, bulk magnetic susceptibility studies, and low-temperature single-crystal magnetic measurements were used to characterize the compound. Magnetic measurements indicate an S = (11)/(2) ground state with the parameters g = 2.03 and D = -0.46 cm(-)(1). Single-crystal magnetic studies show hysteresis of molecular origin at T < 1.2 K with fast quantum mechanical tunneling at zero field.     

Crystal and molecular structure of aN(2)-benzyl-1,3-disubstituted-1,2,3,4-tetrahydro-β-carboline

(1R,3S)-2-Benzyl-3-methoxycarbonyl-1-methylcarboxymethyl-1,2,3,4-tetrahydro-9H-pyrido [3,4-b] indole, C₂₃H₂₄N₂O₄, was synthesized by a modified Pictet-Spengler reaction, and its crystal and molecular structure determined by single crystal X-ray diffraction methods. The crystals are monoclinic:P2₁ (No. 4),a=11.336(1),b=8.919(1),c=10.314(1)Å,=100.81(1)°,Z=2. The structure has been solved by direct methods, and refined toR=0.041 for 2203 observed reflections. The six-membered heterocyclic ring is in a half-chair conformation, and the substituents at C(3) and C(5) occupy axial and equatorial positions respectively. The CH₂Ph group attached to N(4) is in the generally less favoured axial position. The nitrogen atom of the indole system forms an intermolecular hydrogen bond with the carbonyl oxygen of the CH₂CO₂ Me group, the NO distance being 2.995(3)Å.     

Total synthesis of milbemycins: a synthesis of (6R)-6-hydroxy-3,4-dihydromilbemycin E

Following studies using benzyloxymethyl isopropenyl ketone 5 and ethyl 3-(3-furyl)-3-oxopropanoate 6, Robinson reactions between aryloxymethyl isopropenyl ketones 19 and 5 and ethyl 3-(2-trimethylsilyl-3-furyl)-3-oxopropanoate 20 were found to be stereoselective giving cyclohexanones 21 and 41, in which the 3-(arylmethoxy) substituents were cis to the 2-hydroxyl groups, as the major products. After reduction and protection of ketone 21, selective PMB-deprotection, oxidation and stereoselective reduction inverted the configuration at C3 to give the diol 30. Protection of the secondary 3-hydroxyl group followed by modification of the protected 4-alcohol then gave the hydroxybutenolides 36 and 37 after oxidation of the silylated furan using singlet oxygen. The 3-benzyloxycyclohexanone 41 was also converted into the hydroxybutenolide 37 via the (2-trimethylsilylethoxy)methyl (SEM) ether 35. The Wittig reaction between the ylid generated from 2-methylpropyl(triphenyl)phosphonium salt and hydroxybutenolide 36 gave predominantly the (2Z,4Z)-dienyl acid 38 which was taken through to the butenolide 40. Similarly, the racemic hydroxybutenolide 37 was condensed with the racemic ylid derived from phosphonium salt 53 to give, after SEM-deprotection and 5-membered lactone formation, a mixture of the (9Z,2'Z)-dienyl lactones 58 and 59 containing ca. 10% of the corresponding (9Z,2'E)-isomers 60 and 61. (2'Z)/(2'E)-Isomerisation of the dienes 58 and 59 using iodine followed by deprotection gave a mixture of the seco-acids 62 and 63. Selective macrocyclisation of the seco-acid 62 in which the relative configuration of the C1-C7 and C17-C19 fragments (milbemycin numbering) corresponded to that present in the natural milbemycins, gave the beta-milbemycin analogue 65 after butenolide reduction. The hydroxybutenolide 37 was also condensed with the ylid derived from the phosphonium salt 1 and the product taken through to (6R)-6-hydroxy-3,4-dihydromilbemycin E 77. Preliminary attempts to convert the beta-milbemycin analogues 65 and 77 into tetrahydrofurans corresponding to analogues of alpha-milbemycins by treatment with toluene p-sulfonyl chloride under basic conditions gave the primary allylic chlorides 78 and 79.     

The first uranyl-methine carbon bond; a complex with out-of-plane uranyl equatorial coordination

Treatment of [UO2Cl2(thf)3] in thf with one equivalent of [Na(CH(Ph2P = NSiMe3)2)] yields an unusual uranyl chloro-bridged dimer containing a uranium(VI)-carbon bond as part of a tridentate bis(iminophosphorano)methanide chelate complex. The methine carbon is displaced significantly from the uranyl equatorial plane.     

Octanuclear cobalt and nickel cages featuring formate ligands

Two new octanuclear cages are reported which feature formate as a bridging carboxylate which has been formed in situ from decomposition of triphenylacetate used as a ligand.     

Reaction of Some Heterocyclic Formamidines with Trimethylsilylethynyllithium

The reaction of a 2-[(dimethylamino)methyleneamino]pteridine, two 2-[(dimethylamino)methyleneamino]pyrimidines, and a 2-[(dimethylamino)methyleneamino]pyrido[2,3-d]pyrimidine with trimethylsilylethynylithium in the presence of benzyl chloroformate leads to the corresponding 2-[bis(trimethylsilylethynyl)methylamino]-substituted heterocycles. A series of such substrates was prepared and some of the factors which permit this transformation were delineated. An X-ray crystal structure was determined of one of the products - 2-[bis(trimethylsilylethynyl)methylamino]-5,6,7,8-tetrahydro-3-(2,2-dimethylpropanoyloxymethyl)quinazolin-4-one.     

LETTER: Quantum Singularity of Quasiregular Spacetimes

Some of the mildest singularities in classical general relativity are shown to be singular quantum mechanically as well. A class of the mild, topological singularities known as quasiregular singularities remains singular when probed by quantum wave packets. These static spacetimes possessing dislocations and disclinations are quantum-mechanically singular since the spatial portion of the wave operator is not essentially self-adjoint and thus the evolution of a test quantum wave packet is not uniquely determined by the initial wave function.     

The conversion of a pyrrole trimer derivative into a 4,5,6,7‐tetra­hydro‐4‐­(pyrrol‐2‐yl)indol‐7‐yl­tosyl­aminoindole

Vilsmeier formyl­ation of trans‐1‐(4‐methyl­phenyl­sulfonyl)‐2,5‐bis(pyrrol‐2‐yl)­pyrrolidine leads to cleavage of the central ring then a reclosure resulting in the formation of trans‐N‐[2‐formyl‐4‐(5‐formyl­pyrrol‐2‐yl)‐4,5,6,7‐tetra­hydro­indol‐7‐yl]­toluene­sulfon­amide, C₂₁H₂₁N₃O₄S.