Subject xanthates

In a related study, Lusinchi [11] reported the synthesis of a new soluble polymer containing a p-alkoxybenzyl alcohol linker, analogous to Wang resin. The polymer was utilized in intermolecular radical addition reactions. The polymer was synthesized by subjecting xanthate 65, formed in three steps from alcohol 63, to styrene polymerization in the presence of lauroyl peroxide... 

A relevant reductive process, which has found wide application in organic synthesis, is the deoxygenation of alcohols introduced in 1975 by Barton and McCombie [58]. Reaction (4.28) shows that the thiocarbonyl derivatives, easily obtained from the corresponding alcohol, can be reduced in the presence of BusSnH under free radical conditions. The reactivity of xanthates and thiocarbonyl imidazolides [58] was successfully extended to 0-arylthiocarbonates [59] and (9-thioxocarbamates [60]. Several reviews have appeared on this subject, thus providing an exhaustive view of this methodology and its application in natural product synthesis [61-64]. 

Compounds 55 are subjected to cleavage of the xanthate part by H2NCH2CH2NH2 and acid-catalyzed cyclization, which provide dihydrothiophenes 56 (Scheme 13) <2005TL8053>. 

And not only for organic synthesis the reversible addition fragmentation to the thiocarbonylthio motif found in xanthates, dithiocarbamates, dithioesters, trithiocarbonates etc., discussed in Scheme 2 for the particular case of xanthates, is now being actively exploited for the synthesis of bloc polymers. For a recent review, see [75] for the original patents on MADIX and RAFT, see [76,77]. The principle of this approach is summarised in Scheme 38 for the synthesis of a diblock polymer 66. The RAFT and MADIX processes, as they are now called, are set to revolutionise the crafting of polymers with well-defined architectures. It is an extremely effective technique that can be applied to essentially all commercial monomers and is tolerant of many functional groups. Scientific papers and patents on the subject now number in the hundreds. 

This methodology was applied to synthesis of 2/,3/-didehydro-2/,3/-dideoxy-nucleosides, potent anti-HIY agents. The bis-xanthate of the V3-methyluridine derivative was subjected to radical reaction conditions in water, giving the corresponding alkene in 82% yield. Similar results were also achieved in the case of the adenosine derivative (76% yield). However, Kita et al. found that the combination of a water-soluble radical initiator, 2,2 -azobis[2-(2-imid-azolin-2-yl)propane] (VA-061), a water soluble chain carrier, 1-ethylpiperidine hypophosphite (EPHP), and a surfactant, cetyltrimethylammonium bromide (CTAB), resulted in a radical cyclisation that occurred in water with a variety of hydrophobic substrates16 (Table 5.2). 

Starch thiols can have the SH group directly on the pyranose ring or in a side chain. There are several methods of synthesizing starch thiols of the first type. One of them is based on the pyrolysis of starch xanthates (32), but the reaction proceeds in two parallel routes one producing thionates (35) and the other producing thiols (37).2675,2677 Reduction of starch xanthates with NaBPU in alkali is another approach to thiols. Thiols prepared in this manner were subjected to graft polymerization with vinyl polymers. Nucleophilic substitution of the chlorine... 

The importance of polysaccharide derivatives to industry and society is frequently overlooked by, or even unknown to, many chemists. However, those who have an interest in the subject will know of the great economic investment involved in the industrial production of polysaccharide derivatives for inclusion in a wide variety of commodities, such as explosives, synthetic fibers and fabrics, foodstuffs, paints, and plastics. Indeed, several polysaccharide derivatives have been known and commercially exploited for a long time (for example, cellulose xanthate for rayon, and cellulose nitrate for explosives), and, just a few years ago, it might have been claimed that the use of polysaccharide derivatives had reached a peak. 

The tetracyclic core of the berbane and alloyohimbane alkaloids has been accessed using xanthate-based radical chemistry [111]. The precursor xanthate 197 was prepared from tryptamine and then subjected to reflux conditions (1,2-dichloroethane or 2-propanol) in the presence of a catalytic amount of DLP. The resultant piperidones (198 and 200) generated via a 6-exo-trig cyclization were obtained in reasonable yields and accompanied by azepinone 199, the product of presumed radical attack on the 2-position of the indole. The alloyohimbane core was finally accessed through reductive Bischler-Napieralski conditions. 

Compound 108 was subjected to the following sequence of reactions Wittig oleflna-tion with (Et0)2P(0)CH2C02Et, reduction of an ester group with DIBAL-H to obtain 111, Simmons-Smith cyclopropanation, and the corresponding xanthate preparation with NaH-CS2-MeI in THE (Scheme 30.19). 

Freshly produced viscose cannot be spun under normal conditions. It is therefore subjected to what is known as a postripening (maturation) by storing for about 10-100 h at 15-20 C. Here, carbon disulfide is continuously eliminated from the xanthate, and this carbon disulfide partially reforms xanthates and partially reacts with caustic soda to produce sodium trithiocarbonate and sodium sulfide. The primary OH group at the atom of the glucose residue is normally the most reactive. But because of the hydrogen bonding in cellulose, the OH group of the atoms reacts faster than those of... 

Isotropic model filaments after having been subjected to a permanent extension represent orientated systems. They show anisotropy of swelling, optical anisotropy and their X-ray diagram reveals a preferred orientation of the crystallites. At maximum extension a high degree of orientation may be reached. It is highest in xanthate filaments and lowest in filaments stretched in the air-dry state. 

Molybdenum can be detected in steels without removing cuttings by subjecting the sample to an oxidizing etch with nitric acid. The resulting molybdic acid is absorbed in filter paper, which is then tested by the xanthate reaction. ... 

The tricyclic lactone, 163, was also transformed to a yohimbine precursor by Polniaszek and Stevens (Scheme 3.26). Treatment of 163 with methoxide induced a double bond migration which was followed by Michael addition of methoxide. Subsequent oxidation and thermolysis effected selenoxide elimination to provide 166. Ozonolysis of the double bond followed by reduction yielded a mixture of bis-hemiacetals which were reduced with triethylsilane in trifluoroacetic acid to provide the tricyclic pyran 167. Reduction of the lactone and tritylation of the primary alcohol function afforded 168 which was subjected to xanthate ester elimination to give the enol ether 169. Oxymercuration-reduction and detritylation afforded the methylpyranoside... 

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