Cyclic sulfates with nucleophiles

Higher reactivity of 1,3,2-dioxathiolane j/A-dioxides (cyclic sulfates) toward nucleophiles, and practically guaranteed Sn2 stereochemistry of G-O bond cleavage, make them extremely useful synthetic intermediates <1996CHEC-II(4)545, 1997AHC89, 2000T7051>. The starting cyclic sulfates and the products of their reactions with O-nucleophiles are summarized in Table E... 

Reaction of cyclic sulfates with intramolecular O-nucleophiles leads to cyclic ethers and other heterocycles (Table 1). For example, a hydrolysis of compound 39 has produced predominantly the cyclic alcohols 41 (Scheme 4) < 1995JA12873 >. When the reaction was buffered with pyridine, the sulfate ester 40 was isolated rather than the free alcohol. An alcohol function in an intermediate product may give a route to a polysulfate cascade cyclization, which has been successfully realized in the synthesis of poly(tetrahydrofurans) (Table 1) <1995JA12873>. 

Table 1 Reactions of 1,3,2-dioxathiolane S,S-dioxides (cyclic sulfates) with O-nucleophiles... 

Ley et al. (91T9929, 91TL2651) have reported the nucleophilic opening of cyclic sulfates with an anion from 141 (generated from trimethylsilylacet-ylene and methyllithium), which furnished intermediate 142 in the synthesis of valiolactone 143 (Scheme 34). 

Organic azides can be obtained from cyclic sulfates and from cyclic sulfiles (Schane 3.4). Avenoza et al. studied the nucleophilic ring-opening reactions of gm-disubstituted cyclic sulfates with sodium azide, which lead to the synthesis of azido alcohols 37 and 38. They observed that the legioselectivity depends on the substiment present on the cyclic sulfate. Amide substituents lead preferentially to products arising from nucleophilic attack at the least substituted Cp position, whereas reverse regioselectivity is obtained... 

Oxidation of sulfite 59 using RuCh and NaI04 yielded the cyclic sulfate 60 which is now susceptible to nucleophilic attack. Treatment of 60 with NaN3 followed by acid hydrolysis of the intermediate 2-sulfate afforded the trans-i-azido-2-hydroxy derivative 61 (Scheme 3) <1997JOC4277>. 

Nucleophilic substitution on cyclic sulfates 3 with tetramethylammonium fluoride gives 1,2-fluoro sulfates which can be hydrolyzed to l-fluoro-2-hydroxy derivatives.189 Thus propane-1,2-cyclic sulfate 3 affords after hydrolysis l-fluoro-2-hydroxypropane (4). 

Whereas the phosphetanium (Sect. 2.2) derivatives undergo base-catalyzed hydrolysis with essentially complete retention of configuration, the reaction with the related thietanium salts proceeds with complete inversion of configuration and can be described simply as a direct nucleophilic substitution 35. As far as the author is aware, no exchange evidence of the type er countered in the acid-catalyzed hydrolysis of ethylene phosphate, has been found for the cyclic sulfate esters. Consequently despite the geometrical similarities between the cyclic sulfates and phosphates and the related hybridization of the central atoms, the situation in which a finite pentacovalent intermediate sulfur species exists has not been delineated (restricting the discussion to esters). 

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],... 

Cyclic sulfites (68) also are opened by nucleophiles, although they are less reactive than cyclic sulfates and require higher reaction temperatures for the opening reaction. Cyclic sulfite 77, in which the hydroxamic ester is too labile to withstand ruthenium tetroxide oxidation of the sulfite, is opened to 78 in 76% yield by reaction with lithium azide in hot DMF [82], Cyclic sulfite 79 is opened with nucleophiles such as azide ion [83] or bromide ion [84], by using elevated temperatures in polar aprotic solvents. Structures such as 80 generally are not isolated but as in the case of 80 are carried on (when X = N3) to amino alcohols [83] or (when X = Br) to maleates [84] by reduction. Yields are good and for compounds unaffected by the harsher conditions needed to achieve the displacement reaction, use of the cyclic sulfite eliminates the added step of oxidation to the sulfate. 

Increased reactivity toward nucleophiles may render the five-membered cyclic sulfates unstable, for instance, because of an intramolecular nucleophilic attack <1997J(P1)3173>. Thus, when the sulfate 44 is prepared by oxidation of the corresponding sulfite with ruthenium tetroxide, it undergoes a clean rearrangement at room temperature to the isomeric six-membered cyclic sulfate of 2-benzoyloxypropane-l,3-diol (Scheme 5) <1997J(P1)3173>. 

Several recent publications describe cleavage of 1,3,2-dioxathiolane. S -dioxides (cyclic sulfates) by halide nucleophiles that furnish halohydrines, which can be used as synthetic intermediates, primarily for preparation of corresponding epoxides or for further reactions with nucleophiles (Table 6). Similar reactions with chloride have been studied for 1,3,2-dioxathiolane J-oxides (cyclic sulfites) <1996ACS832>. 

The cyclic sulfates undergo ring opening with a wide variety of nucleophiles, such as hydride, azide, fluoride, benzoate, amines, and Grignard reagents. The reaction of an amidine with a cyclic sulfate provides an expeditious entry to chiral imidazolines 21 and 1,2-diamines (Scheme 9.27).169... 

The use of phosphide nucleophiles in an SN2 attack on alkyl-substituted cyclic sulfates allows access to a wide range of phospholane derivatives. However, if aryl-substituted cyclic sulfates are used, elimination and racemization processes compete with substitution. To access bis(2,5-diphe-nylphospholano)ethane (4), an alternative strategy was required (Scheme 13.2).14... 

Cyclic sulfates can even be prepared from diols containing acid-sensitive groups acetonide, silyloxy) by reaction with thionyl chloride and N(C2H5)3 followed by oxidation of the isolated sulfites with Ru04 (catalytic). After reactions with a nucleophile, the resulting sulfate esters can be hydrolyzed by water (0.5-1.0 equiv.) in THF catalyzed by H2S04. The use of a minimal amount of water is crucial for chemoselectivity.2... 

Reactions with nucleophiles. Many of these reactions have been carried out with cyclic sulfate 1, available in 90-93% yield from diisopropyl (+ )-tartrate. This sulfate is reduced at pH 4-5 by sodium cyanoborohydride in THF to diisopropyl (R)-malate in 55% (equation II). 

Meanwhile, PPS liberated phenol in a Tris buffer solution (16). Ethanolamine works similarly and the reaction proceeded first with the expulsion of sulfate by nucleophilic attack of amine followed by liberation of phenol, presumably through the formation of a five-membered cyclic intermediate (Figure 8). Both steps of S042- and phenolate liberation were found to be catalyzed by Mg2+ ion. In Figures 9 and 10 the data are shown for the liberation of phenol. Figure 9 indicates clear rate saturation attributable to complexation in acetonit-... 

The diols (97) from asymmetric dil droxylation are easily converted to cyclic sii e esters (98) and thence to cyclic sulfate esters (99).This two-step process, reaction of the diol (97) with thionyl chloride followed by ruthenium tetroxide catalyzed oxidation, can be done in one pot if desired and transforms the relatively unreactive diol into an epoxide mimic, ue. the 1,2-cyclic sulfate (99), which is an excellent electrophile. A survey of reactions shows that cyclic sulfates can be opened by hydride, azide, fluoride, thiocyanide, carboxylate and nitrate ions. Benzylmagnesium chloride and thie anion of dimethyl malonate can also be used to open the cyclic sulfates. Opening by a nucleophile leads to formation of an intermediate 3-sidfate aiuon (100) which is easily hydrolyzed to a -hydroxy compound (101). Conditions for cat ytic acid hydrolysis have been developed that allow for selective removal of the sulfate ester in the presence of other acid sensitive groups such as acetals, ketals and silyl ethers. 

Cyclic sulfates and sulfamales may serve as substrates for selective nucleophilic substitution with the fluoride ion, e.g. formation of 5. ... 

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