Oxidative Mannich reaction of N-carbobenzyloxy amines with 1,3-dicarbonyl compounds

Efficient carbon-carbon bond formation at the alpha-position of nitrogen was established by one-pot oxidative Mannich reaction of N-carbobenzyloxy (Cbz) amines with 1,3-dicarbonyl compounds using N-tert-butylbenzenesulfinimidoyl chloride as an oxidant.     

Synthesis of ent-thallusin

[reaction: see text] A three-step route from sclareol oxide (6) to bromo ester 4 in 53% overall yield was achieved using the efficient oxidation of an allylic bromide to an enal with bis(2,4,6-trimethylpyridine)silver(I) hexafluorophosphate in DMSO. Stille coupling of bromo ester 4 with stannylpyridine 5 gave the trimethyl ester of ent-thallusin in 54-92% yield by the stoichiometric conversion of 4 to a vinyl palladium intermediate prior to the addition of 5 to the reaction.     

Effects of ambient pressure on Cu Kα X-ray radiation with millijoule and high-repetition-rate femtosecond laser

Hard Cu Kα X-ray radiation was generated with a millijoule and high-repetition-rate Ti: sapphire laser in air, helium or vacuum (2.7–1.3×10⁴ Pa) ambient. The characteristic X-ray was obtained by focusing the 0.06–1.46 mJ/pulse, 100 fs, 1 kHz repetition femtosecond laser onto a solid copper target to a spot 4.8 μm in diameter. The relationship between Kα X-ray conversion efficiency and atmospheric conditions was explained with a simple electron collision model that suggested that the electron mean free path is an important parameter in the generation of ultrafast pulsed X-rays in any ambient condition. We also demonstrated a high-intensity X-ray source working in helium at atmospheric pressure.     

Role of subsurface diffusion and Ostwald ripening in catalyst formation for single-walled carbon nanotube forest growth

Here we show that essentially any Fe compounds spanning Fe salts, nanoparticles, and buckyferrocene could serve as catalysts for single-walled carbon nanotube (SWNT) forest growth when supported on AlO(x) and annealed in hydrogen. This observation was explained by subsurface diffusion of Fe atoms into the AlO(x) support induced by hydrogen annealing where most of the deposited Fe left the surface and the remaining Fe atoms reconfigured into small nanoparticles suitable for SWNT growth. Interestingly, the average diameters of the SWNTs grown from all iron compounds studied were nearly identical (2.8-3.1 nm). We interpret that the offsetting effects of Ostwald ripening and subsurface diffusion resulted in the ability to grow SWNT forests with similar average diameters regardless of the initial Fe catalyst.     

Orientational and positional disorder of ions and its freezing in the CsNO2-TlNO2 system2

The heat capacities of Cs_0.695Tl_0.305NO₂ (Specimen I) and Cs_0.385Tl_0.615NO₂ (Specimen II) have been measured between 14 and 350 K. Specimen I underwent a phase transition at (197.7 ± 0.1) K, with ΔS = (19.2 ± 1.5) JK^?mol^?, and specimen II at (214.5 ± 0.2) K, with ΔS = (5.4 ± 1.0) JK^?1mol^?1, respectively. Above the phase transition, an exothermic temperature drift due to phase separation was observed. Annealing of the sample at 203 K for 300 hr brought about complete phase separation. The solid solution system annealed at 203 K gave two heat capacity peaks at (203.3 ± 0.1) K, with ΔS = (13.8 ± 0.8) JK^?1 mol^?1, and (242.4 ± 0.2) K, with ΔS = (10.6 ± 1.3) JK^?1 for Specimen I, and at (203.0 ± 0.1) K with ΔS = (6.7 ± 0.5) JK^?1 mol^?1, and (257.5 ± 0.2) K with ΔS = (17.9 ± 1.7) JK^?1 mol^?1 for Specimen II. The phase diagram of the CsNO₂-TlNO₂ binary system was constructed on the basis of DTA, heat capacity and dielectric measurements. In the metastable phase, the existence of a residual entropy due to the freezing of a random distribution of Cs⁺₁ and Tl⁺ cations in addition to the orientational disorder of the NO₂^?1 ion was confirmed by a comparison of entropies of the stable and the metastable phases.     

Preparation of optically active 1-acetoxy-2-aryloxypropionitriles and its application to a facile synthesis of (S)-(−)-propranolol

(S)-1-acetoxy-2-aryloxypropionitriles were synthesized by an asymmetric hydrolysis of the racemates with an enzyme. (S)-propranolol, a typical β-adrenergic blocker, was synthesized from (S)-1-acetoxy-2-α-naphthyloxypropionitrile in two steps.     

On the phase transition in α-NH4HgCl3, a two-dimensional version of ammonium chloride

Heat capacity of α-NH₄HgCl₃ crystal has been measured with an adiabatic calorimeter from 11 to 300 K. A sharply peaked anomaly due to an order-disorder change of the ammonium ions was found at 54.97 ± 0.04 K. The entropy and enthalpy changes were estimated to be ΔS = 5.2 ± 1.0JK^?1 mol^?1 and ΔH = 342 ± 65 J mol^?1. In accordance withthe structural two-dimensionality of α-NH₄HgCl₃ crystal, Onsager's solution of the two-dimensional Ising model was used in calculation of the transition temperature. On the assumption that the octopole-octopole interaction is responsible for the ordering of the ammonium ions in the present crystal and in ammonium chloride, the calculation gives 74.44 K for the transition temperature. Several possibilities were discussed for explaining the remaining discrepancy between the observed and calculated transition temperatures.     

Stochastic theory of nonlinear rate processes with multiple stationary states. II. Relaxation time from a metastable state

We have developed a methodology for obtaining a Fokker-Planck equation for nonlinear systems with multiple stationary states that yields the correct system size dependence, i.e., exponential growth with system size of the relaxation time from a metastable state. We show that this relaxation time depends strongly on the barrier heightU(x) between the metastable and stable states of the system. For a Fokker-Planck (FP) equation to yield the correct result for the relaxation time from a metastable state, it is therefore essential that the free energy functionU(x) of the FP equation not only correctly locate the extrema of U(x), but also have the correct magnitudeU at these extrema. This is accomplished by so choosing the coefficients of the FP equation that its stationary solution is identical to that of the master equation that defines the nonlinear system.This work was supported in part by the National Science Foundation under Grant CHE 75-20624.