Cyclic sulfates, conversion

This section outlines three chemical transformations designed to allow further synthetic elaboration of the diols obtained from AD. The first and most broadly applicable method is the conversion of the diols into cyclic sulfates, a functionality that has reactive properties like an epoxide but is even more electrophilic than an epoxide [68]. The second approach to diol activation is the regioselective conversion of one of the hydroxyl groups into a sulfonate ester [69], This approach requires that the diol be substituted in a way that leads to regioselective derivatization of one of the two hydroxyl groups, and diol esters are a prime example of such... 

The use of cyclic sulfates in synthetic applications has been limited in the past because, although cyclic sulfites are easily prepared from diols, a convenient method for oxidation of the cyclic sulfites to cyclic sulfates had not been developed. The experiments of Denmark [70] and of Lowe and co-workers [71 ] with stoichiometric ruthenium tetroxide oxidations and of Brandes and Katzenellenbogen [72a] and Gao and Sharpless [68] with catalytic ruthenium tetroxide and sodium periodate as cooxidant have led to an efficient method for this oxidation step. Examples of the conversion of several diols (67) to cyclic sulfites (68) followed by oxidation to cyclic sulfates (69) are listed in Table 6D.7. The cyclic sulfite/cyclic sulfate sequence has been applied to 1,2-, 1,3-, and 1,4-diols with equal success. Cyclic sulfates, like epoxides, are excellent electrophiles and, as a consequence of their stereoelectronic makeup, are less susceptible to the elimination reactions that usually accompany attack by nucleophiles at a secondary carbon. With the development of convenient methods for their syntheses, the reactions of cyclic sulfates have been explored, Most of the reactions have been nucleophilic displacements with opening of the cyclic sulfate ring. The variety of nucleophiles used in this way is already extensive and includes H [68], [68,73-76], F" [68,72,74], PhCOCT [68,73,74], NOJ [68], SCN [68],... 

Alternatively, the remaining sulfate ester of 70 may serve as a leaving group for a second nucleophilic displacement reaction. When this displacement is by an intramolecular nucleophile, a new ring is formed, as was first shown in the synthesis of a cyclopropane with malonate as the nucleophile [68] and of aziridines with amines as the nucleophiles [76]. The concept is further illustrated in the double displacement on (/J,/ )-stilbenediol cyclic sulfate (72) by benzamidine (73) to produce the chiral imidazoline 74 [79]. Conversion of the imidazoline (74) to (.V,.S )-stilbenediaminc 75 demonstrates an alternative route to optically active 1,2-diamines. Acylation of 75 with chloroacetyl chloride forms a bisamide, which, after reduction with diborane, is cyclized to the enantiomerically pure trans-2,3-diphenyl- 1,4-diazabicy-clo[2.2.2]octane (76) [81],... 

The heading substitution reactions has been used to describe the conversion of a stereogenic center to another. Of course, this means that the substrate stereogenic center has had to be obtained by one of the reaction types outlined earlier, from the chiral pool, or by resolution. Reactions that fall into this category include epoxide and cyclic sulfate openings and iodolactonizations (Chapter 22). Perhaps the most important reaction of this type for asymmetric synthesis is allylic substitution in the presence of a transition metal catalyst. 

Dioxathiolane 2,2-dioxides (cyclic sulfate esters of 1,2-diols) are used in practice like sultones to introduce acid substituents into nitrogen heterocycles (48BSF1002), especially into cyanine dyes (58GEP1028718). Fluorinated derivatives are useful in the treatment of textiles such as cotton to impart wash and wear characteristics (62USP3055913). The conversion of cyclic sulfates into resinous film-forming polymers has been likewise patented (64USP3154526). 

Reaction of cyclic sulfates or thionocarbonates, derived from 1,2-diols, with telluride results in stereospecific alkene formation <1995TL7209>. This is illustrated by the conversion of the cyclic sulfate OTitra-l,2-diphenyl-l,2-ethanediol 49 into fif-stilbene exclusively by Te, as shown in Equation (13). Treatment of the cyclic sulfate of 47-1,2-diphenyl-1,2-ethanediol with Te produces /ra r-stilbene exclusively. These results are accounted for by intermolecular Te Sn2 displacement followed by intramolecular Sn2 displacement to form the corresponding tellurirane. The tellurirane then thermally loses tellurium stereoselectively forming alkene. Cyclic sulfates need not be used dimethanesulfonates or di-/i-toluenesulfonates prepared from 1,2-diols also, stereospecifically, provide alkenes via telluriranes <1993CC923, 1996SL655>. 

Quinoline-containing 1,2,4-trioxolanes such as 107 have been patented as anti-malarial agents <05FRP2862304>. Further results on the reactivity of the novel 13,2-dioxathiolane-2-thione containing the cyclic thionosulfite function have appeared <05HCA1451> and a convenient method for direct conversion of 1,2-diols into cyclic sulfates using sulfuryl chloride has been described <05TA3908>. 

We have already seen how cyclic sulfates such as 123 can be converted into amino alcohols that might have been made by amino hydroxylation. The conversion of 1,2-diols, made by the AD reaction, into epoxides has been very widely used. A combination of acetyl bromide and an orthoester gives a bromo-acetate via an oxonium ion 182. The ion is formed with retention, bromide opens it with inversion at the benzylic centre, and epoxidation in base inverts it again. The net result is retention.39... 

Oi,R.and Sharpless, K.B. (1991) Stereospecific conversion ofchirall,2-cyclic sulfates to chiral imidazolines. Tetrahedron Letters, 32, 999-1002. 

Other Unsaturated Compounds. - The dienals 13 (with D-xylo-, D-lyxo- and D-arahino-configurations) have been condensed with the phosphonate 14 to give the enone adducts 15 the intramolecular Diels-Alder reactions of these adducts are mentioned in Chapter 22. Treatment of the unsaturated lactone 16 with the Tebbe reagent has afforded 17 its conversion into a cyclooctene derivative is covered in Chapter 18. Exposure of the cyclic sulfate 18 to base has afforded a mixture of the exo- and endo-olefins 19 and 20, ° and a syn-selective dihydroxyla-tion of the 3,4-unsaturated pyranoside 21 generated predominantly the D-allo product. Synthesis of the branched-chain 5,6-ene 22 using standard methods, and its conversion into a cyclitol during the first total synthesis of (—)-tetracyc-line is mentioned in Chapter 22. 

The base-catalysed ring-contraction of 5-lactone 2-triflates to homochiral tetrahydrofurans (Vol. 26, p. 169) now has a complementary acid catalysed procedure, as exemplified by the conversion of 23 to 24, and of 25 to 26, on treatment with HQ in methanol at room temperature. Under these conditions, the triflate 27 gave the expected product, but with K2CO3 in MeOH the bicyclic oxetane 28 was obtained in 86% yield, a result rationalized by a mechanism involving initial P-elimination fiom 27. Cyclic sulfates can also be used to make anhydroaldonic acids, as... 

Although these equations held true for some strains of bacteria under some growth conditions, they did not help explain the commonly observed quantitative conversion of both sulfur atoms of thiosulfate to sulfate, rather than the liberation of the sulfane-sulfur mainly as elemental sulfur. During the 1960s, cyclic reactions of polythionates and other polysulfur compounds continued to be postulated as mechanisms for thiosulfate and polythionate metabolism (Trudinger 1967), but none of these was supported at the time by strong biochemical evidence. The time was opportune for a new approach to the problem of thiosulfate oxidation in thiobacilli. 

The cyclizations of 85 to 86 and of 87 to 88 represent the simple cases in which the internal nucleophile is the OH group of an alcohol [64,65]. An in situ generated hydroxy group, as in the addition of alcohols to carbonyl compounds, can also participate in phenylseleno-etherification reactions. This is examplified by the conversion of 89 into 90 in the presence of benzyl alcohol [66]. Another type of OH, which gives rise to these reactions is the enolic OH of /1-dicarbonyl compounds. Thus, Ley reported that compounds like 91 and 93 can be transformed into the cyclic derivatives 92 and 94 by treatment with N-PSP 11 in the presence of zinc iodide [67]. The cyclization of 95 to 96 represents a simple example of the selenolactonization process [68, 69]. It is interesting to note that the various cyclization reactions indicated in Scheme 14, which require different electrophilic selenenylating agents, can all be effected with phenyselenyl sulfate [70]. 

Figures 1 and 2, respectively, show the old and new processes. The major innovations are use of (1) a spray dryer absorber in place of the wet venturi, absorber, centrifuge, rotary dryer combination (2) a cyclic hot-water reheat system interconnecting thermally the calciner product solids and the effluent gas from the spray dryer absorber and (3) a coal-fired, fluidized-bed reactor for conversion of magnesium sulfite (MgSO ) and sulfate (MgSO ) to MgO and SO gas. Otherwise, the two systems are very similar, utilizing a regenerable absorbent to recover the sulfur material as a usable commercial grade of concentrated sulfuric acid.

Syntheses of 5,6- and Other Unsaturated Cyclic Compounds - A general approach to enol ethers, illustrated by conversion of nitro-alkene 37 into 38 by treatment with tetrabutylammonium hydrogen sulfate-potassium fluoride, has been described. The reaction was also found to be applicable to a wide range of acyclic sugars (see Section 4 below). 

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