Silver mesylate

O-isopropylidene derivative (57) must exist in pyridine solution in a conformation which favors anhydro-ring formation rather than elimination. Considerable degradation occurred when the 5-iodo derivative (63) was treated with silver fluoride in pyridine (36). The products, which were isolated in small yield, were identified as thymine and l-[2-(5-methylfuryl)]-thymine (65). This same compound (65) was formed in high yield when the 5 -mesylate 64 was treated with potassium tert-hx Xy -ate in dimethyl sulfoxide (16). The formation of 65 from 63 or 64 clearly involves the rearrangement of an intermediate 2, 4 -diene. In a different approach to the problem of introducing terminal unsaturation into pento-furanoid nucleosides, Robins and co-workers (32,37) have employed mild base catalyzed E2 elimination reactions. Thus, treatment of the 5 -tosylate (59) with potassium tert-butylate in tert-butyl alcohol afforded a high yield of the 4 -ene (60) (37). This reaction may proceed via the 2,5 ... 

Another synthetic route via the Beckmann rearrangement, which is promoted by organoaluminum reagent along with alkylation, involves a new stereoselective reduction of the imino group. The starting oxime sulfonate (228) was synthesized from cyclopentanone (226) in three steps Reaction of 226 with 1-undecene in the presence of silver oxide produced the a-undecylcyclopentanone (227) which on successive treatment with hydroxylamine and methanesulfonyl chlo-ride-triethylamine gave the mesylate (228). Treatment of the oxime mesylate... 

The corresponding 1-O-mesyl ester has been obtained24 by shaking a dry benzene solution of the same bromide with finely powdered silver meth-anesulfonate for two days at room temperature. 

The total synthesis of ( + )-Erysotramidine (2) has been described by Ito et al. (137) starting from the amide (174) (Scheme 39). After O-mesylation to 177, base-catalyzed reaction gave the cyclopropane derivative (178) which with zinc in acetic acid was reduced to 179, which was identical to the product (135) of O-methylation of 172. Conversion of 178 to the thioketal (180) was followed by reaction with phenylselenyl chloride. A mixture of two compounds, 181 and 182, was produced the former could be transformed quantitatively to the latter. Finally, treatment of 182 with silver nitrate in methanol gave 183, which was then desulfurized to yield erysotramidine (2). 

The presence of catalytic amounts of cuprous triflate or silver(I) sulfonates exerts a remarkable influence on the activation energy and regiochemistry of alkynyl(phenyl)-iodonium tosylate and mesylate decompositions5,6. Such reactions proceed in acetonitrile at room temperature and afford moderate yields of alkynyl tosylates and mesylates (equations 82 and 83)5,6. It is noteworthy, however, that the treatment of alkynyliodonium triflates (R = n-Bu, r-Bu) with cuprous triflate in acetonitrile does not afford alkynyl triflates6. Silver(I) catalysis has similarly been applied to the conversion of bis(alkynyliodo-nium) tosylates to bisalkynyl tosylates (equation 84)43. As might be expected, mono-tosylate esters are also produced in these reactions. 

The silver-catalyzed cycloisomerization of allenic carboxylic acids to butenolides was also reported by Marshall and co-workers.329 Starting from the enantiomerically enriched propargyl mesylate 390, palladium-catalyzed hydroxycarbonylation led to the chiral allenecarboxylates 391 which afforded the butenolides 392 upon treatment with silver nitrate (Scheme 114). Unfortunately, partial racemization could not be avoided in this two-step sequence. In a related study, Ma and Shi330 have shown that the combination of Pd(PPh3)4 and Ag2C03 promotes the cyclization of allenecarboxylates to the corresponding butenolides, accompanied by the introduction of aryl or alkenyl groups at C3. 

A short efficient synthesis of cycloartenol from 3j8-acetoxylanost-24-en-ll/8-yl nitrite has been achieved. Irradiation of the nitrite in carbon tetrachloride solution in the presence of oxygen afforded the nitrate ester (30) which was converted into cycloartenol via the olefin (31) and the mesylate (32). The structure of abietospiran (33), the main component of the crystalline coating which is responsible for the silver-grey colour of the bark of Abies alba, has been... 

With compound 64 available, vanadyl acetylacetonate catalyzed epoxidation [44] accompanied by simultaneous cyclization, afforded the corresponding tetrahydrofuran and its diastereomer in a 4 1 ratio (Scheme 12). Ring expansion of the corresponding mesylate 65 with silver (I) carbonate afforded compound 66 in a 42% yield for the two steps [45]. Extension of the side chain in six steps, followed by an asymmetric epoxidation, gave product 67 stereoselectively. The cyclization of 67 with titanium tetraisopropoxide in a manner consistent with model studies [27d], afforded bicyclic ether 68 in 65% yield. Transformation to the epoxide under standard conditions afforded fragment 69 ready to be coupled with the D-ring side chain. 

C-17, gave 3 -melhanesulphonyloxyandrost-5-en-17 -ol acetate (403). Diborane addition to the A -double bond and oxidation afforded the 6-keto-derivative (404). Elimination of the 3-mesylate, followed by iodine and silver acetate treatment furnished the 2-acetoxy-3-alcohol (405), which was successively acetylated at C-3, brominated at C-7, and dehydrobrominated to the triacetoxy-A -6-ketone (406). Enol acetylation of the conjugated carbonyl furnished the tetra-acetate (407), which was treated with peracid and then hydrolysed and isomerized at C-5 to yield the desired tetraol (408). ... 

Reaction of steroidal tosylates with KNO2 in DMSO or DMF gave reasonable yields of alcohols with inverted configuration. The previously reported epi-merization at C-3 during Raney nickel-catalysed hydrogenation of methyl 3, 1 a-dihydroxy-12-oxo-5/8-cholanate was incorporated in a report of the synthesis of 3/3,7a,12j8-trihydroxy-5/3-cholanic acid and the 3a,7a,12/3-trihydroxy-analogue. Conversion of mestranol into epimestranol was achieved by treatment of the 17-mesylate with silver nitrate in aqueous THF. ... 

D-Glucosyl dibenzylphosphates, (29) - (31) have been prepared by reaction of the corresponding (-glycosyl bromide with silver di-benzylphosphate and their reactions towards sodium azide investigated. Monodebenzylation occurred in each case and sulphonates at C-6 were displaced but 4-0-sulphonates were unreactive. Thus the 6-tosylate (29) gave the azide (32), the 4,6-dimesylate (30) gave the 6-azido-4-O-mesyl product (33), whereas the 4-0-mesylate (31) did not... 

Silhar et al. [127] investigated three alternative fluorination reagents (DAST, C4F9SO2F and Deoxo-Fluor) for the conversion of hydroxymethyl purine 87 into 90 using different bases and also pre-conversion of the hydroxyl group to a mesylate (88) or iodide (89) and treatment with AgF (Scheme 34). Ultimately, it was found that the silver fluoride displacement of the iodide was the most general route affording A7-benzyl-6-(fluoromethyl)purine 90 in isolated yields of between 72 and 84 %. 

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