Ethers s. a. Alkoxy compounds

Alkoxy compounds s. a. Ethers, Polyalkoxy compounds l-Alkoxy-l-cyclohexen-3-ones... 

Model experiments [43] using aliphatic alcohols (6) indicate that the main products with lead tetraacetate are cycHc ethers (mainly tetrahydrofuran derivatives) and carbonyl compounds, the product ratio depending on the solvent. Cyclic ethers are predominant in neutral non-polar solvents e.g. refluxing benzene), but carbonyl compounds are favoured by polar or basic solvents, especially p5uidine. These results were interpreted in terms of competing homolytic and heterolytic processes. The initial step is thought to be reversible formation of an alkoxy-lead triacetate (7), which may suffer either a rapid polar elimination of and Pb(OAc)s" by the action of base to give a ketone (8), or a slower homolysis of the alkoxy-lead... 

Attempts to attack the i4a-methyl group of lanosterol from a 9a-alkoxy-radical gave only a 9,io-seco-9-ketone [53], although the 7a-alkoxy radicai readily formed a cyclic ether with the I4a-methyl group [54]. Finally, a selection of secondary alkoxy-radicals derived from alcohols adjacent to quaternary centres e.g. la- or ij8-0H [55], 3j5-OH-4,4-dimethyl [56], 17/S-OH [36J, and 2i-OH-20-cyclic ketal [56]) gave fragmentation products which were either unsaturated carbonyl compounds, or acetoxy derivatives resulting from combination of alkyl and acetoxy radicals, e.g. ... 

A high degree of stereoselectivity can be realized under chelation control, where an oxygen atom of an ether function (or more generally a Lewis base) in the a-, P- or possibly y-position of carbonyl compounds can serve as an anchor for the metal center of a Lewis acid. Since Cram s pioneering work on chelation control in Grignard-type addition to chiral alkoxy carbonyl substrates [30], a number of studies on related subjects have appeared [31], and related transition state structures have been calculated [32], Chelation control involves Cram s cyclic model and requires a Lewis acid bearing two coordination sites (usually transition metal-centered Lewis acids). 

The more obvious choice for a model compound corresponds to exactly one repeat unit of the polymer. The a-ethoxy-m-(4-n-alkoxy-4 -cyanobiphenyl)s exhibit nematic mesophases at n=4-9 and SmA mesophases at n = 8-ll, and therefore match the thermotropic behavior of the polymer better than the vinyl ether monomer. However the SmA mesophase is enantiotropic only at n = 11, and the nematic mesophase is monotropic at all of these spacer lengths. Compounds which take into account only the mesogen and spacer are also good, if not better, models of the polymers. In contrast to the ethyl ethers, all of the SmA and most of the nematic mesophases are enantiotropic, which means that the melting temperature mimics the relative temperature of the glass transition of the polymer backbone better. However, the nematic mesophase still appears at n = 6 -11, and the SmA mesophase doen t appear at n = 5-7, 10, 11. 

Sodium azide does not react with carbonyl sulfide to form 5-hydroxy-1,2,3,4-thiatriazole, nor with carboxymethyl xanthates, RO CS SCH2COOH, to form 5-alkoxy-l,2,3,4-thiatriazoles. The latter, however, could be prepared from xanthogenhydrazides (RO-CS-NHNH2) and nitrous acid. They are very unstable and may decompose explosively at room temperature only the ethoxy compound (6) has been examined in detail. This is a solid which decomposes rapidly at room temperature and even at 0°C is transformed after some months into a mixture of sulfur and triethyl isocyanurate. In ethereal solution at 20° C the decomposition takes place according to Eq. (16) C2H6O—CSNs -----------------------> C2H6O—CN+S+Na (16)... 

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