Disulfones eliminative

Disulfonate esters of vicinal diols sometimes undergo reductive elimination on treatment with sodium iodide in acetone at elevated temperature and pressure (usually l(X)-200°). This reaction derived from sugar chemistry has been used occasionally with steroids, principally in the elimination of 2,3-dihy-droxysapogenin mesylates. The stereochemistry of the substituents and ring junction is important, as illustrated in the formation of the A -olefins (133) and (134). 

The conditions adopted in this procedure favor the production of a-monosulfonate in a state of high purity at the expense of a high conversion of anthraquinone. A better conversion can be achieved by conducting the sulfonation at a higher temperature, or by using more oleum, but in either case there is a considerable increase in the amount of disulfonic acids formed. The extent of /3-sulfonation is not influenced greatly by the temperature, but is dependent chiefly on the amount of mercuric salt present in the solution. The amount specified corresponds approximately to the limit of solubility of the salt in the acid employed, and very little of the /3-acid is formed. As the potassium /S-sulfonate is more soluble than the a-salt, traces of this isomer are easily eliminated by crystallization. 

Reactivity toward nucleophiles and comparison with other electrophilic centers 152 Paths for nucleophilic substitution of sulfonyl derivatives 156 Direct substitution at sulfonyl sulfur stereochemistry 157 Direct substitution at sulfonyl sulfur stepwise or concerted 158 The elimination-addition path for substitution of alkanesulfonyl derivatives 166 Homolytic decomposition of a-disulfones 172 10 Concluding remarks 173 Acknowledgement 174 References 174... 

With these radicals, spontaneous C(6)-0 heterolysis is slow ( < 10 s" ). However, if the electron density of the system is increased by OH -induced de-protonation of N(l)-H, 02 elimination is observed [23, 24, 25]. With the peroxyl radical from 5,6-dihydrouracil-6-yl, the heterolysis rate constant is 8.3 X 10 s the reaction leading to the isopyrimidine derivative shown [37]. The reaction is perfectly analogous to the eliminations of the radical anions of nitrobenzenes (Eq. 15) or anthraquinone-2,6-disulfonate (Eq. 18). 

Starting from the appropriate sulfonylated acetals 105, 106, and 107 (from 2,5-anhydro-D-ribose, -D-xylose, and -D-lyxose, respectively), the application of a method for elimination of vicinal, secondary disulfonates by reaction with sodium iodide in lV,IV-dimethylformamide in the presence of zinc112 has permitted"3 the preparation of the... 

Hadjidemetriou [25] has carried out a comparative study of the determination of nitrates in calciferous soils by the phenoldisulfonic acid and the chromotropic acid spectrophotometric methods. He used 0.02 N cupric sulfate as soil extractant. Silver sulfate was added to remove chlorides. Nitrites, if present, were eliminated by acidifying the extract with N in sulfuric acid. The phenol disulfonic acid method is subject to interference by other ions. Details of the chromotropic acid method are given below. 

Acyclic carbohydrate derivatives containing unsaturation, with some exceptions, exhibit much of the chemistry already described for cyclic analogues, and their usefulness should not be overlooked. Unsaturated derivatives of alditols can be made, for example, by standard eliminations from alditol v/r-disulfonates or epoxides or by /f-eliminations from O-substituted 1-deoxy-l-nitroalditols and 1-deoxy-l-sulfonylalditols. Additions of hydrogen and ammonia to the unsaturated nitroalditols made in this way offer, respectively, routes to 2-deoxy- and 2-amino-2-deoxyaldoses.255... 

In the previous subsection, it was shown that the Ferrier reaction offers an opportunity to convert glycal derivatives into unsaturated sugar derivatives, which have an isolated double bond between C(2) and C(3). The Tipson-Cohcn reaction is another important reaction for the introduction of isolated double bonds.29 In this procedure, a cis or tram diols are converted into disulfonates (mesylates or tosylates) which are reductively eliminated with sodium iodide and zinc in refluxing DMF (Scheme 3.6a). In this reaction, the C(3) sulfonate is substituted by an iodide, which then is reductively removed by zinc with concomitant elimination of the second sulfonate moiety, introducing a double bond. Stereoelectronic effects make nucleophilic substitutions at C(3) more favourable than similar reactions at C(2) (see Section 3.2.3). Probably, the elimination proceeds through a boat conformation. In this case, the iodide and tosylate are in a syn relation. In most cases, E2 elimination proceeds via a transition state involving an anti orientation. Nevertheless, syn elimination becomes the dominant mode of reaction when structural features prohibit an anti orientation. 

The reactions used in the preparation of intermediates are, for the most part, simple operations. Frequently, they proceed quantitatively according to the rules of stoichiometry. In other cases, side reactions are encountered which complicate the reaction and greatly reduce the yield. It is one of the important tasks of the dye chemist to study these undesirable side reactions suflSciently to understand their nature and then, if possible, to select the reaction conditions which will favor only the main reaction leading to the desired intermediate. This end is not always attained, because often the set of conditions which will eliminate the side reactions is not known, but the chemist must always bear in mind the possibihty of achieving diese conditions by further study. The preparation of l,8-aminonaphthol-3,6-disulfonic acid (H acid) illustrates this point. This compound has been known for nearly fifty years and is still being studied extensively in many laboratories, yet to this day has not been prepared in satisfactory yield. 

In a few cases pyrolysis and ring contraction occurs under simultaneous loss of carbon-fragments (mostly ethano units because of synthetic reasons). The benzylic side of the disulfone undergoes recombination, whereas the ethano bridge and both the SO2 groups become cleaved and eliminated. 

The generation of an alkene by the reaction of a v/c-disulfonate ester with iodide (the Tipson-Cohen reaction) has been known since 1943 and in some cases it has proved useful where other methods have failed, as in the preparation of the spirocyclic triene (54 Scheme 22). The mechanism probably involves an initial nucleophilic displacement to give an iodohydrin sulfonate, which then undergoes iodide-induced elimination to the alkene. Methanesulfonates can be used as well as arenesulfonates. 

Although there is no proof for the mechanism, many of the data known about the reaction can be interpreted in terms of three general steps (1) sulfonation (XXII to XXIV) (2) formation of a m- or p-disulfonic acid with the elimination of an alkyl carbonium ion if one of these positions is occupied (XXIII to XXVII and XXIII to XXIV) and (3) displacement of the more hindered sulfonic acid group by the eliminated carbonium ion (XXIV to XXVI and XXVII to XXVIII) or an oxonium ion (XXVII to XXIX). In agreement with (3) it has been found that the most hindered sulfonic acids are the most readily desulfonated.67... 

A novel method for the synthesis of alkenes is based on the coupling of aldehydes with dithioacetals to give the corresponding hydroxy thioacetals, which afford vicinal disulfides via reductive phenylthio migration.242 The syn-diastereomers are the major products from symmetrical compounds while the anti-isomers are obtained with high selectivity with unsymmetrical compounds. Separation of the diastereomers, oxidation to the 1,2-disulfones, and reductive elimination give the corresponding alkenes with moderate stereoselectivities (Eq. 137).242... 

The mechanism of the elimination from the 5,6-disulfonates most probably involves nucleophilic displacement of the primary sulfonyloxy group (see other iodo-p-tolylsulfonates, on p. 101), followed by a second attack by iodide on the iodine, and by a concerted elimination of the secondary ester grouping. An elimination also occurs when 1,2-0-... 

The preceding section dealt primarily with the evidence that demonstrated sulfenes to be intermediates in these processes and also, where the evidence warranted it, with the mechanism of the sulfene formation. A continual point of concern is whether or not the reaction is really proceeding by way of the sulfene or not. In this section we shall attempt to find what circumstances of substrate, base and (where different) nucleophile tend to lead to the elimination-addition (sulfene) reaction, and which to some other process, notably the direct displacement reaction. Sometimes, indeed, it takes only a rather small change in conditions to alter the mechanism completely. For example, it has been noted above that azide ion reacts with a-disulfones or sulfonyl chlorides by the direct displacement49. This is also seen in the reaction of methanesulfonyl chloride with aqueous sodium azide when the... 

Inhibiting Side Reactions. As stated in a preceding section, undesired by-product sulfone formation is pronounced in the mono- and disulfonation of ai matic hydrocarbons such as benzene, toluene, or xylene with SO or strong oleum. The addition of acetic acid (about 5 per cent by weight of the hydrocarbon) inhibits, but does not eliminate, sulfone formation. Sodium sulfate and sodium benzenesulfonate are also said to inhibit sulfone formation from benzene. In sul nating dodecylbenzene detergent alkylate with SO3, sulfone formation does not occur as it does with benzene or toluene, but sulfonic anhydride formation does occur. This objection-... 

Elimination. vic-Disulfonates react wii temperature (11 examples, 85-96%). threo-W Z)-alkenes. 

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