A Practical Approach to Synthesize the C(9)-C(24) Fragment of (+)-Discodermolide

A practical and stereoselective synthesis of the C(9)–C(24) subunit of (+)‐discodermolide has been achieved. The strategy featured the construction of the key intermediate Z‐trisubstituted vinyl iodide 12 from the dibromo‐olefin 6 via an efficient modified Tanino‐Miyashita's approach. The union of the two fragments was carried out through a Suzuki cross‐coupling reaction.     

Practical approach to thermally stimulated discharge (TSD) method on polymers

The paper deals with the thermally stimulated discharge current (TSD or TSDC) method; exclusively with the short circuited one. Because of its low effective frequency, TSD has excellent resolving power. Problems both of measurement and of the evaluation are analyzed. The effects of experimental circumstances and theoretical considerations are demonstrated by results on different polymers and model calculations as well. In order to get reliable results, the sample preparation must be performed carefully. It is particularly valid in case of solution cast samples. The depolarization curve of a real polymer is always complex, consisting of superimposed relaxation processes. This fact causes unexpected problems in the evaluation. Heating rate slightly affects the peak separation; however, high heating rate might produce thermal inhomogeneity in the sample.     

Practical access to the polymer incarcerated platinum (PI Pt) catalyst and its application to hydrogenation

Polymer incarcerated platinum catalysts (PI Pt) were conveniently prepared from PtCl(2)(COD) or H(2)PtCl(6).6H(2)O and styrene copolymers via reduction of the Pt sources with triethylamine, coacervation, and cross-linking. The Pt catalysts have been successfully applied to catalytic hydrogenation including saturation of heterocyclic compounds.     

格尔德霉素C(11)～C(21)片段的合成

以D-三乙酰葡萄糖烯为最初原料,经三步反应合成了已知内酯化合物5.以羰基α位亚甲基化、底物诱导的不对称催化氢化反应为关键步骤,构建了关键的C(14)位手性中心.最终,经10步反应、以24%的总产率合成了苯醌安莎霉素类天然产物格尔德霉素(Geldanamycin)的C(11)~C(21)片段.     

Practical aziridinations II: electronic modifications to poly(pyrazolyl)borate-copper catalysts

A significant influence of the electronic features of poly(pyrazolyl)borate ligands on the efficiency of the copper-catalyzed aziridination reaction has been noted. Electron-deficient, bidentate di(pyrazolyl)borates in conjunction with copper(II) chloride generated the most effective catalyst system for the aziridination of a variety of olefins.     

(p-Dimethylaminophenyl) Diphenylphosphine: A More Practical Phosphine in the Mitsunobu Reaction

The Mitsunobu reaction has been of much use in general synthetic organic chemistry. The major drawback of this reaction has been the removal of the by-products triphenylphosphine oxide and the dialkyl hydrazinedi-carboxylate. We report here that (p-dimethylaminophenyl)diphenylphosphine, an alternative phosphine, greatly assists the work-up procedure of this useful reaction.     

Practical formal total synthesis of (rac)- and (S)-camptothecin

A practical, efficient and scalable formal total synthesis of (rac)- and (S)-camptothecin is described, which proceeds via the known DE ring building blocks 19 and (S)-19, respectively. The racemic synthesis starts from diethyl oxalate and uses straightforward carbonyl chemistry in order to generate the pyridone ring system. 19 was formed in 8.4% overall yield over 9 linear steps avoiding any chromatographic purification. The asymmetric version of this approach encompassed a diastereoselective Grignard addition to the enantiomerically pure alpha-ketoester 30 in order to generate the (S)-configured quaternary stereocenter. The auxiliary could be recycled in high yield and was successfully reused multiple times. The final steps paralleled the racemic approach. (S)-19 was thus prepared in 9.4% overall yield (er = 95 : 5) over 10 steps.     

Practical synthesis of Dirhodium(II) tetrakis[N-phthaloyl-(S)-tert-leucinate

An efficient and reliable procedure for the preparation of dirhodium(II) tetrakis[N-phthaloyl-(S)-tert-leucinate], Rh2(S-PTTL)(4), a universally effective catalyst for a range of enantioselective carbene transformations, is described. The N-phthaloylation of (S)-tert-leucine by the method of Bose with essentially no racemization is a key to this process.     

Practical synthesis of (Z)-polyaromatic and heteroaromatic vinylacetylenes

[reaction: seet text] Two synthetic routes to several (Z)-polyaromatic and heteroaromatic substituted vinylacetylenes are described. The nature of aryl- or heteroaryl-substituted carboxaldehyde used as starting material dictated the choice of Wittig salt employed. A very attractive way to construct polyaromatic and pyridine-containing enynes is the reaction of polyaromatic and pyridine-containing aldehydes with bromomethyltriphenylphosphonium bromide in the presence of potassium tert-butoxide followed by a Sonogashira desilylation procedure (method B).     

A New Practical Preparation of bis(Trimethylsilyl) Peroxide

Bis(trimethylsilyl) peroxide can be readily obtained by reaction of trimethylchlorosilane with the hexamethylenetetramine-hydrogene peroxide complex.     

A practical guide to the staggered herringbone mixer

An analytical model of mixing in the staggered herringbone mixer (SHM) was derived to estimate mixing parameters and provide practical expressions to guide mixer design and operation for a wide range of possible solutes and flow conditions. Mixing in microfluidic systems has historically been characterized by the mixing of a specific solute system or by the redistribution of flow streams; this approach does not give any insight into the ideal operational parameters of the mixer with an arbitrary real system. For Stokes-flow mixers, mixing can be computed from a relationship between solute diffusivity, flow rate, and mixer length. Confocal microscopy and computational fluid dynamics (CFD) modeling were used to directly determine the extent of mixing for several solutes in the staggered herringbone mixer over a range of Reynolds numbers (Re) and Péclet numbers (Pe); the results were used to develop and evaluate an analytical model of its behavior. Mixing was found to be a function of only Pe and downstream position in the mixer. Required mixer length was proportional to log(Pe); this analytical model matched well with the confocal data and CFD model for Pe<5 x 10(4), at which point the experiments reached the limit of resolution. For particular solutes, required length and mixing time depend upon Re and diffusivity. This analytical model is applicable to other solute systems, and possibly to other embodiments of the mixer, to enable optimal design, operation, and estimation of performance.     

Practical preparation method of polymer-incarcerated (PI) palladium catalysts using Pd(II) salts

[reaction: see text]. Polymer-incarcerated (PI) palladium catalyst was practically prepared from inexpensive Pd(II) salts and a polystyrene-based copolymer under reducing conditions. Remarkable effects of alkali metal salts on the palladium loading were observed. PI Pd thus prepared showed high catalytic activity in Mizoroki-Heck reactions and Suzuki-Miyaura couplings with a range of substrates including an aryl chloride. In all cases, the Pd catalyst was recovered quantitatively without leaching, and reused several times without significant loss of activity.