Synthesis and Structural Characterization of a New Macrocyclic Polysiloxane-immobilized Ligand System

A new porous solid macrocyclic 1,4,7,11,14-pentaazapentadecane-3,15-dione polysiloxane ligand system of the general formula P–(CH₂)₃–C₁₁H₂₂O₂N₅ (where P represents [Si–O]_n siloxane network) has been prepared by the reaction of polysiloxane-immobilized iminobis(N-(2-aminoethyl)acetamide) with 1,3-dibromopropane. The FTIR and XPS results confirm the introduction of the macrocyclic functional ligand group into the polysiloxane network. The new macrocyclic polysiloxane ligand system exhibits high potential for the uptake of metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺).     

Electron transfer at an encapsulated cobalt(III) centre: kinetics of oxidation of thiourea and 1,1,3,3-tetramethyl-2-thiourea in aqueous acidic media

Summary The stoichiometries, kinetics and mechanisms of oxidation of (NH₂)₂CS (1) and (Me₂N)₂CS (2) to the corresponding disulphides by Co^IIIM (M = W₁₂O₄₀ ^∞-) in aqueous HC1O₄ were investigated. The reaction with (1) follows the empirical rate law- d[oxidant] = k[reductant][oxidant] where k = 12.5 ± 0.3 m⁻¹ s⁻¹ at 25° C, while that with (2) follows the equation- d[oxidant] = a + b [reductant] [reductant] [oxidant] where a = 5.4 × 10⁴ M⁻¹s⁻¹ and b = 3.3 × 10⁶M⁻² s⁻¹ at 25° C. Free radicals are important in the reactions and possible reaction mechanisms are suggested and discussed.     

Synthesis of a chiral steroid ring D precursor starting from carvone

A chiral five-membered, silyl enol ether containing, steroid ring D precursor has been synthesized from carvone. This silyl enol ether has been applied in the synthesis of a chiral C17 functionalized steroid skeleton using the addition of a carbocation, generated with ZnBr₂ from a Torgov reagent, followed by cyclization of the adduct by treatment with acid.     

Metallation of pyridines and quinolines in the presence of a remote carboxylate group. New syntheses of heterocyclic quinones

2-(3- and 2-Pyridylcarbonyl)benzoic acids (2,3), 2-(2-pyridylcarbonyl)thiophene-3-carboxylic acid (6), 2-(3-quinolylcarbonyl)benzoic acid (10), and most of the corresponding esters (compounds 1,7 and 9 ) are readily synthesized and involved in a deprotonation-condensation sequence. Biologically active aza-anthraquinones such as benzo[g]isoquinoline-5,10-dione (2-azaanthraquinone, 4 ) and benzo[g]quinoline-5,10-dione (1-azaanthraquinone, 5) are prepared using the strategy. Extension to other heterocyclic quinones such as thieno[3,2-g]quinoline-4,9-dione (8) and benzo[j]phenanthridine-7,12-dione (11) is also investigated.     

Synthesis of 7H-pyrido[2,3-c]carbazoles from 5-bromo-8-methoxyquinolines via coupling and azide cyclization reactions

A new strategy for the synthesis of substituted 7H-pyrido[2,3-c]carbazoles has been developed from substituted 5-bromoquinolines by using cross-coupling reaction with (2-aminophenyl)boric acids, followed by a regioselective azide cyclization.     

Some uses of mischmetall in organic synthesis

Mischmetall, an alloy of the light lanthanides, has been used in a variety of organic reactions, either as a coreductant in samarium(II)-mediated reactions (Barbier and Grignard-type reactions, pinacolic coupling reactions) or as the promoter of Reformatsky-type reactions. It has been also employed as the starting material for easy syntheses of lanthanide trihalides, the reactivity of which has been explored in Imamoto and Luche–Fukuzawa reactions and in Mukaiyama aldol reactions.     

Synthesis of the c14-c25 subunit of bafilomycin A1

The enantioselective synthesis of the C14-C25 subunit of bafilomycin A1 was realized in a convergent route. The sequence involves two dynamic kinetic resolution steps of 2-alkyl 1,3-diketones that use optically active ruthenium complexes, an anti-selective reduction of a beta-hydroxyketone to control the C23 stereogenic center, and an aldol-type reaction under Evans' conditions, which sets the C17 and C18 stereogenic centers.