Rapid methylation on carbon frameworks useful for the synthesis of 11CH3-incorporated PET tracers: Pd(0)-mediated rapid coupling of methyl iodide with an alkenyltributylstannane leading to a 1-methylalkene

The Pd(0)-mediated rapid coupling of methyl iodide with an excess of alkenyltributylstannane was examined with the aim of incorporating a short-lived 11C-labeled methyl group into a biologically significant organic compound with a 1-methylalkene unit for the synthesis of a PET tracer. Four sets of reaction conditions (A-D) were used, all performed in DMF at 60 degrees C for 5 min. Condition B, using CH3I/stannane/Pd2(dba)3/P(o-tolyl)3/CuCl/K2CO3 (1:40:0.5:4-6:2:5), works well in almost all cases. Condition D, using CH3I/stannane/Pd2(dba)3/P(o-tolyl)3/CuX (X = Br, Cl, or I)/CsF (1:40:0.5-5:2-20:2-20:5-50), shows the best results with regard to general applicability to tin substrates, affording the corresponding methylated product in >90% yield based on consumption of methyl iodide. P(t-Bu)2Me was less effective than P(o-tolyl)3, particularly for alpha,beta-unsaturated carbonyl substrates. No regio- or stereoisomerization occurred under these reaction conditions. The efficiency of the protocol was demonstrated by synthesis of an 11C-methylated compound.     

Metal enolates of alpha-CF3 ketones: theoretical guideline, direct generation, and synthetic use

The difficulty as well as the significance of the direct generation of metal enolates of alpha-CF(3) ketones cannot be easily understood by chemists unfamiliar with F. In sharp contrast to the sunny side of non-F, hydrocarbon chemistry, F chemistry has long been overshadowed. Metal enolates of carbonyl compounds are synthetically important in C-C bond-forming reactions. However, the metal enolates of fluorinated carbonyl compounds have been severely limited to alpha-F metal enolates. Alpha-CF(3) metal enolates have generally been recognized as unstable and difficult to prepare because of the facile beta-M-F elimination. However, we have developed a direct generation and synthetic application of alpha-CF(3) metal enolates. Therefore, the present results regarding the direct generation and synthetic use of metal enolates of alpha-CF(3) ketones might be recognized as a real breakthrough for the general use of metal enolates in F chemistry.     

Steroidal alkaloid glycosides, esculeosides C and D, from the ripe fruit of cherry tomato

Two new steroidal alkaloid glycosides, esculeosides C and D, have been isolated from the ripe fruit of Cherry tomato [Lycopersicon esculentum var. cerasiforme (DUNAL) ALEF.], along with three known steroidal alkaloid glycosides, esculeoside A, esculeoiside B, and lycoperoside G. Their chemical structures were determined on the basis of spectroscopic data.     

Highly stereoselective asymmetric Pummerer reactions that incorporate intermolecular and intramolecular nonbonded S...O interactions

New chiral sulfoxides (R(S),S)-3, (S(S),S)-3, (R(S),S)-4, and (S(S),S)-4 and known chiral sulfoxides (R(S))-5, (R(S))-6, and (R(S))-7 were synthesized, and the stereochemistry of the new sulfoxides (R(S),S)-3 and (R(S),S)-4 was determined by X-ray crystallographic analysis. In their crystallographic structures, the intramolecular nonbonded S...O close contacts were recognized. Analyses of several sulfoxide complexes including rac-11 with N,N-dimethylacetamide (DMAC) or N-methyl-2-pyrrolidone (NMP) in a MeOH solution utilizing cold-spray ionization mass spectrometry provided, for the first time, direct information for intermolecular nonbonded S...O interactions between sulfoxides and amide (or lactam) in a solution. Highly diastereoselective and enantioselective Pummerer reactions based on the concept of intermolecular and intramolecular nonbonded S...O interactions were performed by treatment of several chiral sulfoxides (R(S), S)-3, (S(S), S)-3, (R(S), S)-4, (S(S), S)-4, (R(S))-5, (R(S))-6, and (R(S))-7 with acetic anhydride and trimethylsilyl triflate (TMSOTf) in DMAC, NMP, N,N-dimethylformamide, and N-formylpiperidine. Mechanistic studies on these facile stereoselective Pummerer reactions revealed the necessity for the amide/TMSOTf complex, such as 26 or 27, to be an efficient activation reagent for Ac(2)O and a trapping reagent for the released acetate ion, and that DMAC and NMP had a positive effect on this highly stereoselective chiral transfer reaction.     

Metropolis–Hastings Algorithms with acceptance ratios of nearly 1

We develop the results on polynomial ergodicity of Markov chains and apply to the Metropolis–Hastings algorithms based on a Langevin diffusion. When a prescribed distribution p has heavy tails, the Metropolis–Hastings algorithms based on a Langevin diffusion do not converge to p at any geometric rate. However, those Langevin based algorithms behave like the diffusion itself in the tail area, and using this fact, we provide sufficient conditions of a polynomial rate convergence. By the feature in the tail area, our results can be applied to a large class of distributions to which p belongs. Then, we show that the convergence rate can be improved by a transformation. We also prove central limit theorems for those algorithms.     

Fast scintillation detectors for high-energy X-ray region

We have developed fast scintillation detectors for nuclear resonant scattering experiments using synchrotron radiation and a nuclear excited level existing in >30?keV. A fast x-ray detector using an organic-inorganic perovskite scintillator of phenethylamine lead bromide (PhE-PbBr₄) had a dominant light emission with a fast decay time of 9.9?ns. An x-ray detector equipped with a 0.9-mm-thick PhE-PbBr₄ crystal (size: ～8 × 7?mm²) was used to detect nuclear resonant scattering in ⁶¹Ni (the first excited level: 67.41?keV; half-life: 5.3?ns). We could successfully record the decaying gamma rays emitted from ⁶¹Ni with a relatively high detection efficiency of 24%. A lead-doped plastic scintillator (NE142, Pb ～5?wt% doped) had been known to have a faster decay time of 1.7?ns. Following a test of a single NE142 detector, a four-channel NE142 detector was fabricated and successfully applied to the synchrotron-radiation based M?ssbauer spectroscopy experiment on ⁶¹Ni.     

Improved resolution for aerial imaging by retro-reflection with two transparent spheres

Optical Review - This paper proposes a method to improve the modulation transfer function (MTF) of aerial images by combining an aerial imaging optical system by retro-reflection with conjugated...