Ethers symmetrical, unsymmetrical

Ethers can be symmetrical, where the two alkyl groups are the same, or unsymmetrical, where the two alkyl groups are different. While diethyl ether is symmetrical, ethyl methyl ether is unsymmetrical. The common name of an unsymmetrical ether is obtained by quoting the names of the two alkyl groups in alphabetical order followed by the prefix ether. 

Ethers are prepared from alkyl halides by the treatment of metal alkoxide. This is known as Williamson ether synthesis (see Sections 4.3.6 and 5.5.2). Williamson ether synthesis is an important laboratory method for the preparation of both symmetrical and unsymmetrical ethers. Symmetrical ethers are prepared by dehydration of two molecules of primary alcohols and H2SO4 (see Sections 4.3.7 and 5.5.3). Ethers are also obtained from alkenes either by acid-catalysed addition of alcohols or alkoxymercuration-reduction (see Section 5.3.1). 

Moricini and Kelly [75] have reported the synthesis of spiro-fi-lactams 6 containing an exocyclic double bond (Scheme 2) by the 1,2-dipolar cycloaddition of symmetrically/unsymmetrically substituted allene 4 with chlorosulfonyl isocyanate 5 in ether. 

Problem 9.12 Draw the organic product of each reaction and ciassify the product as an alcohol, symmetrical ether, or unsymmetrical ether. 

Simple ethers are commonly called alkyl alkyl ethers. The name consists of a hst of the alkyl (or aryl) groups in alphabetical order followed by the name ether. For example, an unsymmetrical ether with an -butyl group and a methyl group is named -butyl methyl ether. Symmetrical ethers are named by using the prefix di- along with the name of the alkyl group. For example, an ether with two isopropyl groups is called diisopropyl ether. 

Ethers are described as symmetrical or unsymmetrical depending on whether the two groups bonded to oxygen are the same or different Unsymmetrical ethers are also called... 

The following section describes a versatile method for preparing either symmetrical or unsymmetrical ethers that is based on the principles of bimoleculai nucleophilic substitution. 

This reaction, which is named after W. Williamson, is the most important method for the synthesis of unsymmetrical ethers 3. For this purpose an alkoxide or phenoxide 1 is reacted with an alkyl halide 2 (with R = alkyl, allyl or benzyl). Symmetrical ethers can of course also be prepared by this route, but are accessible by other routes as well. 

Silyi enol ethers can be dimerized to symmetrical 1,4-diketones by treatment with Ag20 in DMSO or certain other polar aprotic solvents." The reaction has been performed with R , R = hydrogen or alkyl, though best yields are obtained when r = r = H. In certain cases, unsymmetrical 1,4-diketones have been prepared by using a mixture of two silyi enol ethers. Other reagents that have been used to achieve either symmetrical or cross-coupled products are iodosobenzene-Bp3-Et20," ceric ammonium nitrate," and lead tetraacetate." If R =0R (in which case the substrate is a ketene silyi acetal), dimerization with TiCU leads to a dialkyl succinate (34, r =0R)." ... 

This Is such a simple strategy that it is worth solving the problem of removing one carbonyl group. The best way turns out to be to reduce (10) all the way to the symmetrical ether (11) and then to add one carbonyl group after condensation to (12) has made the molecule sufficiently unsymmetrical. 

Product 117 is a convenient starting compound for the subsequent modification of photochromes. Publication (09TL1614) gives an efficient synthetic route to both symmetrical 118 and unsymmetrical 119 phenyl-substituted dihetarylethenes bearing amino, hydroxy, or carboxy groups based on a Suzuki reaction of dichloride 117 with commercially available substituted boronic acids (or their pinacol esters) in a dimethyl ether (DME)-H20 mixture (4 1). For the symmetrical products, the yields are 85-95% for the unsymmetrical products, they are 60%. 

Following this work on NMR spectra of ozonides, there is an extensive paper by the Griesbaum group" where 35 ozonides (6-14 with different stereochemistries) have been studied. The widely different structures examined allowed the influences of structural features on "O NMR spectra of ozonides to be shown. Five structurally different types of ozonides can be recognized symmetrically tetrasubstituted (type 6), unsymmetrically tetrasubstituted (type 7), unsymmetrically tri- and tetrasubstituted (type 8), unsymmetrically disubstituted (type 9-13) and bicyclic ozonides (type 14). "O NMR chemical shifts of peroxidic and ethereal oxygens are collected in Table 3. All spectra were obtained at natural isotopic abundance, in benzene-dg solution mainly at 25 °C, although in some cases higher temperatures had to be used. These experimental conditions make for an easy comparison with the previously discussed data. 

Williamson ether synthesis preparation of ether The sodium or potassium alkoxides are strong bases and nucleophiles. Alkoxides (RO ) can react with primary alkyl halides to produce symmetrical or unsymmetrical ethers. This is known as Williamson ether synthesis. The reaction is limited to primary alkyl halides. Higher alkyl halides tend to react via elimination. For example, sodium ethoxide reacts with ethyl iodide to produce diethyl... 

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