Direct synthesis with methylene chloride

Core-shell nanoparticles can also be fabricated using microemulsions. This was performed using a two-stage microemulsion polymerization beginning with a polystyrene seed [62]. Butyl acrylate was then added in a second step to yield a core-shell PS/PBA morphology. The small microlatex led to better mechanical properties than those of similar products produced by emulsion polymerization. Hollow polystyrene particles have also been produced by microemulsion polymerization of MMA in the core with crosslinking of styrene on the shell. After the synthesis of core-shell particles with crosslinked PS shells, the PMMA core was dissolved with methylene chloride [63]. The direct cross-... 

In a variation of this synthesis, the amidine is N-halogenated prior to its condensation with an isothiocyanate ester the resulting IV-haloimidoyl-thioureas (238) are readily cyclized to 239 by alkalis. By employing bromine in conjunction with methylene chloride-aqueous alkali as the reaction medium, the reaction may be performed in one operation. 3-Trichloromethyl-5-(substituted)amino-l,2,4-thiadiazoles have been produced by this method.187 The use of potassium ethyl xanthate similarly yields the 5-ethoxy analogs (240 e.g., R = CC13, R1 = Et) directly, with elimination of the elements of hydrogen sulfide.188... 

Aromatic aldehydes are also easily dimethylated by Me2TiCl2, and aromatic acyl chlorides form r-butyl derivatives directly when treated with an excess of Me2Zn/TiCU in methylene chloride. Some examples are also known of application of such a reaction in the synthesis of natural products. ... 

Peptide synthesis. Sheehan and co-workers used this water-soluble reagent for a simplified and rapid synthesis of tetra- and pentapeptides without isolation of intermediates. The reagent (I. I equiv.) is added to a solution of the N-carbobenzoxy-amino acid (I equiv.), the amino acid ester hydrochloride or peptide ester hydrochloride (1 equiv.), and triethylamine (1 equiv.) in methylene chloride. After I hr. at room temperature the solution was washed successively with water (to remove excess reagent and the urea), dilute hydrochloric acid, and sodium bicarbonate solution. The curbobenzoxy group Is removed by hydrogenolysis and the product used directly in the next step. ... 

A soln. of crude cyclohexyl trimethylsilyl ether and triphenylcarbonium fluoroborate in methylene chloride stirred 9 hrs. at room temp, under Ng cyclohexanone. Y 92%. - This is part of a 2-step mild oxidation of alcohols to oxo compds. in high yields. F. e. s. M. E. Jung, J. Org. Chem. 41, 1479 (1976) with nitrosyl fluoroborate, also oxidation of alkoxystannanes, and direct oxidation of alcohols, s. G. A. Olah and T.-L. Ho, Synthesis 1976, 609. 

Considerable interest has been expressed in the development of direct methods for the synthesis of a-hydroxy ketones using nontoxic hypervalent iodine reagents and which involve the foUowing methods reaction of a ketone with iodobenzene diacetate in the presence of potassium hydroxide in methanol and then hydrolysis of the dimethylacetals oxidation of the enol sUyl ether of acetophenone using the s) tem iodosobenzene/boron trifluoride efherate/water in methylene chloride at—40°C and reaction of ketones with [fcis(trifluoroacetoxy)]iodobenzene and trifluoroacetic acid in acetonitrile-water under acidic conditions. "... 

Tomoi and coworkers adopted a somewhat more direct approach in their synthesis of 16-crown-5 derivatives bearing a single alkenyl residue. They hoped to obtain precursors to polymers which could be used as phase transfer catalysts. In this approach I,I-bis-chloromethylethylene (a-chloromethallyl chloride) was allowed to react with the dianion of tetraethylene glycol (NaH/THF). By this method, methylene-16-crown-5 could be isolated in 66% yield after vacuum distillation. Ozonolysis led, in almost quantitative yield, to the formation of oxo-16-crown-5 as shown in Eq. (3.38). These authors prepared a number of other, closely related species by similar methods. 

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