Benzoyl xanthate

Benzoyl chloride and sodium isopropyl xanthate gave a mixed anhydride that was stable to pyridine catalyst, but a 2-year-old sample had turned to isopropyl ben2oate (16). 

Cross, Charles F (1855 1935) British scientist, a pioneer in modern cellulose chemistry his prepn of acetyl benzoyl celluloses (1889-90) was a prelude to the great achievement of his career, the discovery of cellulose Na xanthate (viscose) which Was patented under the names of Cross, Bevan Beadle (1892). Cross E.J. Bevan published "Textbook of Papermaking (1887), "Cellulose, an Outline of the Structural Elements of Plants (1895), Wood Pulp and Its Applications (1911), and numerous other Works on every aspect of cellulose. The pioneer work and the persistent successful efforts of Cross were duly recognized during his life. He was awarded the medal of the Society of Chemical Industry... 

This problem is not so severe when acyl xanthates are used as precursors because these substrates absorb in the visible region, while the products do not (however, the products might still be recycled to the radical pool by radical addition-elimination). Visible light photolysis of benzoyl xanthane (42) and allyl acetate provides (43) in 60% yield. Standard (ionic) 3-elimination of the xanthane is a facile reaction that gives (44). When the tertiary acyl xanthane (45) is irradiated in the presence of W-benzylmaleimide... 

Much more critical, however, is the introduction of the 2 -deoxy function. This can be achieved after selective 3 -0-benzoylation to 170, xanthation at the 2 position to 171 and reductive cleavage (Bu3SnH) to 172 following Barton s method [91]. Further radical ring opening by the Hullar-Hanessian procedure and final reduction leads to the D-C disaccharide 173 [92],... 

A mixture of methyl xanthate (0.4 mmol) and Bu2POH (dibutylphosphine oxide, 2.0 mmol) in dry dioxane (3 ml) was refluxed under an argon atmosphere, and then a solution of benzoyl peroxide (0.4 mmol) in dioxane (3 ml) was added dropwise to the mixture. After 90 min, the solvent was removed and the residue was chromatographed on silica gel to give the reduction product [22]. 

We conceived that, if the alcohol was to be deoxygenated to a radical, an olefinic linkage would be formed by -elimination of a phenylsulfonyl radical. The xanthate function is a convenient radical source and gave the olefin in about 80% yield in toluene under reflux using AIBN or benzoyl peroxide as initiators and Ph2SiH2.22... 

The reaction of the secondary xanthate 1009 and pyrrole 1008 afforded methyl 2-(5-benzoyl-17/-pyrrol-2-yl)pro-panoate 1010 in high yield, a new representative of 2-arylpropionic acids constituting a large class of nonsteroidal antiinflammatory drugs, which are used worldwide (Equation 238) <2003CC2316>. 

The use of a low-molecular-weight sulphur-containing photoinitiator, such as S-benzoyl O-ethyl xanthate (BEX) is described for the polymerization of MMA [133], Laser flash photolysis of BEX reveals [134] that the primary photoprocess involves a C(=0)-S cleavage to generate both the benzoyl and the ethoxythio-caibonylthiyl radicals which initiate the polymerization (Scheme 34). 

Poly(S -benzoyl O-ethylmethacrylate xanthate) resin [poly(BEMX)], obtained by functionalization of crosslinked 2-hydroxyethyl methacrylate/ethyleneglycol dimethacrylate beads, results [135], upon irradiation at 400 nm, in a heterogeneous photoinitiator for the polymerization of MMA and styrene more effective than the low-molecular-weight analogue BEX. 

Young and Wood (389) did not isolate the intermediate benzoyl dithiocarbazic acids (LXXXII) which readily loose hydrogen sulfide on warming to yield the 5 substituted zl4-l,3,4-oxadiazoIine-2-thiones (LXXXIII). These authors suggested another reaction mechanism involving the intermediate formation of a xanthate type salt (LXXXVI) through nucleophilic attack of the enol form of the carboxylic acid hydrazide (LXXXIb) on carbon disulfide. 

Inner chelates (uncharged chelates) are formed when metal ions react with bifunctional ligands, such as dithizone (formula 1.1), 8-hydroxyquinoline [14] (formula 1.2), dithiocarbamates (formulae 1.3 and 1.4), ethyl xanthates [15,16], cupferron (formula 1.5), BPHA (N-benzoyl-N-phenylhydroxylamine) [17,18], acetylacetone (formula 1.6) and thenoyltrifluoroacetone (HTTA) (formula 1.7) [19,20]. 

Hydroxy sulfones can be easily transformed into derivatives for radical-mediated reactions such as thiobenzoates,220 xanthates,221,222 selenoben-zoates,221,222 and thionocarbonates.221,222 These substrates may be used in subsequent stereoselective syntheses of alkenes by free radical methods. Methyl xanthates usually give the best results in the olefination reaction, typically using O-acyl A - It y d roxy- 2 - thiopy ri d o n e under visible light irradiation. Alternatively, diphenylsilane in combination with radical initiators such as Et3B/02, benzoyl peroxide, or AIBN may also be used (Eq. 127).221 222... 

It is a useful reagent for deoxygenating phosphine oxides to phosphines, and will redueed chiral phosphine oxides to chiral phosphines with retention of eonfiguration [Marsi J Org Chem 39 265 1974]. It is a reducing agent in radical reactions [Perez et al. J Org Chem 52 5570 1967], and deoxygenates primary and seeondaty alcohols via their xanthate or thionocarbonate esters (prepared from aryl-OCSCl and an inhibitor, e.g benzoyl peroxide) in 60-100 minutes in >87% yields [Barton et al. Synlett 435 7997]. [Beilstein 16 III 1198,16 IV 1360.]... 

Glycosides and Simple Derivatives Thereof. — Methyl 2,3,4-tri-O-benzoyl-0-D-xylopyranoside, methyl 2,3,4,5-tetra-0-acetyl-o -D-galactoseptanoside, 2-pyridyl l-thio-/3-D-glucopyranoside, the three methyl xanthates of methyl 4,6-... 

The 2-deoxy-derivative was obtained from the known 2,6-dideoxy-L-arahi/to-hexono-l,4-lactone, while the 4-deoxy-derivative was obtained by radical reduction of an O-protected L-ifaamnose 4-xanthate derivative. The 3-deoxy-derivative (42) was obtained from L-rhamnose via a mixture of acetylated L-rhamnono-1,4-lactone (41) and its 1,5-lactone istnner, utilizing hydrogenolytic conditions that effect elimination of acetic acid and stereoselective reduction of the resulting 3-deoxy-hex-2-enonolactone (Scheme 7). 2- and 4-Deoxy-L-rhamnose exist mainly in the pyranose form in solution, whereas 3-deoxy-L-ifaamnose (38) forms a mixture of pyranose and furanose forms in the ratio 2 1. Similar reactions have been used to convert benzoylated... 

Phosphorus-based hydrogen donors were investigated with the goals of having a low-cost, metal-free reagent amenable to large scale deoxygenations of xanthates and thionocarbonates Dimethyl and diethylphosphite were successfully used for the reduction of xanthate 38 to 39, however, AIBN could not be used as initiator and was replaced with benzoyl peroxide. 

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