Syndiospecific living polymerization of 4-methylstyrene with (trimethyl)pentamethylcyclopentadienyltitanium/tris(pentafluorophenyl)borane/trioctylaluminium catalytic system

The polymerization of 4-methylstyrene with the (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃)/tris(pentafluorophenyl)borane (B(C₆F₅)₃)/trioctylaluminium (AlOct₃) catalytic system at –20°C was carried out. The number-average molecular weight (M_n) of the polymers increased linearly with increasing monomer conversion. The propagating chain ends were successfully reacted with tert-butyl isocyanate, and the M_n of the polymer determined by ¹H NMR was in good agreement with the M_n determined by GPC measurement. It is concluded that this catalytic system promoted the syndiospecific living polymerization of 4-methylstyrene.     

Purification of quinoline yellow components using high-speed counter-current chromatography by stepwise increasing the flow-rate of the mobile phase

Quinoline yellow (Color Index No. 47005) consists of multiple components that show a large difference in their partition coefficients (K), ranging from 0.03 to 3.3 in the solvent system tert.-butyl methyl ether (MTBE)-1-butanol-acetonitrile-aqueous 0.1 M trifluoroacetic acid (TFA). Consequently, it requires an excessively long elution time for the simultaneous separation of all components by the standard high-speed counter-current chromatography technique, which uses a constant flow-rate of the mobile phase. In order to overcome this problem, we increased the flow-rate of the mobile phase stepwise from 0.1 to 2.0 mL/min. Using this new procedure, six components (0.2-6.1 mg) were successfully isolated from 25 mg of a commercial quinoline yellow preparation in a single run using a two-phase solvent system composed of MTBE-1-butanol-acetonitrile-aqueous 0.1 M TFA (1:3:1:5, v/v). The purified components were analyzed by high-performance liquid chromatography, electrospray ionization mass spectrometry, and nuclear magnetic resonance spectroscopy.     

A variant of inclusion-exclusion on semilattices

Let (S,∪) be a finite join-semilattice and (D, ∨, ∧) be a distributive lattice. Let $\text{?:S→D}$ be a map satisfying $\text{?(x ∪ y) ? ?(x) ∧ ?(y)}$ for each x and y in S. Then for any valuation v on D the following identity holds.

$\text{v}\text{?}\text{xυS}\text{f(x)}\text{=}\text{∑}\text{cυC}\text{(?1)}{}^{\mathrm{l(c)}}\text{v}\text{?}\text{xυc}\text{f(x)}$

where C is the set of all chains in S and l(c) denotes the length of a chain c. Also the theorem can be dualized.     

Rapid ‘on-column’ preparation of hydrogen [11C]cyanide from [11C]methyl iodide via [11C]formaldehyde

Hydrogen [¹¹C]cyanide ([¹¹C]HCN) is a versatile ¹¹C-labelling agent for the production of ¹¹C-labelled compounds used for positron emission tomography (PET). However, the traditional method for [¹¹C]HCN production requires a dedicated infrastructure, limiting accessibility to [¹¹C]HCN. Herein, we report a simple and efficient [¹¹C]HCN production method that can be easily implemented in ¹¹C production facilities. The immediate production of [¹¹C]HCN was achieved by passing gaseous [¹¹C]methyl iodide ([¹¹C]CH₃I) through a small two-layered reaction column. The first layer contained an N-oxide and a sulfoxide for conversion of [¹¹C]CH₃I to [¹¹C]formaldehyde ([¹¹C]CH₂O). The [¹¹C]CH₂O produced was subsequently converted to [¹¹C]HCN in a second layer containing hydroxylamine-O-sulfonic acid. The yield of [¹¹C]HCN produced by the current method was comparable to that of [¹¹C]HCN produced by the traditional method. The use of oxymatrine and diphenyl sulfoxide for [¹¹C]CH₂O production prevented deterioration of the molar activity of [¹¹C]HCN. Using this method, compounds labelled with [¹¹C]HCN are now made easily accessible for PET synthesis applications using readily available labware, without the need for the ‘traditional’ dedicated cyanide synthesis infrastructure.

In a reaction column, gaseous [¹¹C]methyl iodide was converted to [¹¹C]formaldehyde in a first layer containing N-oxide and then transformed into hydrogen [¹¹C]cyanide in a second layer containing hydroxylamine-O-sulfonic acid within 2 minutes.     

Syndiospecific living polymerization of 4‐methylstyrene and styrene with (trimethyl)pentamethylcyclopentadienyltitanium/tris(pentafluorophenyl)borane/trioctylaluminum catalytic system

The polymerizations of styrene and 4‐methylstyrene (4MS) with a half‐metallocene type catalytic system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminum (AlOct₃), and tris(pentafluorophenyl)borane [B(C₆F₅)₃] were investigated at ?25 °C. The addition of AlOct₃ as a third component of the catalytic system is effective both to promote the syndiospecific polymerization and to inhibit the nonstereospecific polymerization at the low‐temperature region. The use of AlOct₃ was also effective to eliminate the chain transfer reaction to alkylaluminum. The number‐average molecular weights (M_n's) of poly(4MS) or polystyrene increased proportionally with increasing monomer conversion. The molecular weight distribution (MWD) of polymer stayed narrow [M_w/M_n = ～ 1.1 for poly(4MS) and M_w/M_n = ～ 1.5 for polystyrene]. It was thus concluded that the polymerizations of the styrenic monomers with Cp*TiMe₃/B(C₆F₅)₃/AlOct₃ catalytic system proceeded under living fashion at ?25 °C. The living random copolymerization behaviors of styrene and 4MS were also confirmed. The ¹³C NMR analysis clarified that each of the homopolymers and random copolymers obtained in this work had highly syndiotactic structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3692–3706, 2001     

Total Synthesis of Terprenin,a Highly Potent and Novel Immunoglobulin E Antibody Suppressant

Regioselective halogenations and Suzuki reactions ensure proper linkage of the aromatic rings in two total syntheses of terprenin ( 1 ). Both routes make it possible to prepare 1 efficiently and in large quantity.