Diols sulfites

The chemistry of this class of complexes is dominated by the 7r-allyliron tricarbonyl lactone complexes (155), which have been studied extensively and reviewed. Compounds (155) are normally prepared by reaction of vinyl epoxides with a source of Fe(CO)4 , such as (1) and photolysis, (2) and heat, or (2) in Tetrahydrofinan (THF) or with ultrasonication (see Sonication) the latter two methods are considered to be superior. It has been reported that butene-1,4-diols, particularly the cis isomers, (with or without Lewis acids), 3-butene-1,2-diol sulfites, 3,6-dihydrooxazmes, or related compounds also give (155) with (2). The complexes are isolated as anti isomers at C-1. Substituents at C-3 are oriented syn when not constrained in a ring, whereas... 

Although the Sharpless asymmetric epoxidation is an elegant method to introduce a specific defined chirality in epoxy alcohols and thus, in functionalized aziridines (see Sect. 2.1), it is restricted to the use of allylic alcohols as the starting materials. To overcome this limitation, cyclic sulfites and sulfates derived from enantiopure vfc-diols can be used as synthetic equivalents of epoxides (Scheme 5) [12,13]. 

This reagent combination also converts carboxylic acids to acyl chlorides (see Section 3.4.1). The mechanistic basis for the special effectiveness of benzotriazole has not yet been determined, but it seems likely that nucleophilic catalysis is involved. Sulfinyl ester intermediates may be involved, because Z-2-butene-l,4-diol gives a cyclic sulfite ester with one equivalent of reagent but the dichloride with two equivalents. 

The 1,2-cyclic sulfites are readily obtained from anomeric mixtures of 1,2-diols by reaction with sulfinyl diimidazolide as mixtures of exo- and endo-isomers at sulfur (Scheme 4.34) [312-314],... 

The cyclic sulfites were first found to react with lithium phenoxides as nucleophiles in DMF in a one-pot procedure commencing from the unprotected diol [357]. Subsequent work opened up this class of donor to alcohol nucleophiles in conjunction with the use of a Lewis add, such as Yb(OTf)3 or Ho(OTf)3, to activate the donor in refluxing toluene (Scheme 4.57) [314,358,359]. The very high degree of P-selec-tivity observed in these reactions is consistent with an SN2-like displacement of the sulfite oxygen. 

The endiol-cyclic sulfite 19 obtained by oxidation of the dihydropyran 18 affords a trans-fused bipyran <99TL2235> and this system is also accessible from the sulfonyl-stabilised oxirane 20 (Scheme 6) <99TL8019>. 

SO(Im)2, generated from thionyl chloride and imidazole, is quite effective in the formation of cyclic sulfites from 1,2-diols. For example, furo[2,3,- -l,3,2-dioxathiole 53 was produced by reacting SO(Im)2 with diol 88. In a similar reaction, compounds 89a and 89b yielded 55a and 55b, respectively (Equations 12 and 13) <20040L3913, 2005JME4276>. 

The reaction of m-3,4-di- /t-butylthiolone-3,4-diol 74 with thionyl chloride and base (triethylamine or pyridine) produced two diastereomeric cyclic sulfites 3a and 3b. The ratio of 3a to 3b is dependent on the solvent used (Table 3). These teactions are generally high yielding with a greater tendency for the formation of diastereomer 3a (Equation 25) <2003HAC587>. 

The chemical transformation must not affect the stereogenic centers. Suitable acyclic candidates are compounds with easily convertible functional groups, such as diols, diamines, amino alcohols, dicarboxylic acids and so on. A number of procedures known before 1973 have been compiled, including conversion of diols and amino alcohols into sulfites or 1,3-dioxolanes by thionyl chloride, or acetalization with ketones31,1"319, as well as the conversions of dinitriles into imides320, dicarboxylic acids into cyclic anhydrides or imides321, and hydroxy acids into oxazolidones 322. 

Rose oxide is usually prepared from citronellol which can be converted into a mixture of two allyl hydroperoxides (e.g., by photosensitized oxidation with oxygen). Reduction of the hydroperoxides with sodium sulfite yields the corresponding diols [183]. Treatment with dilute sulfuric acid results in allylic rearrangement and spontaneous cyclization of one of the isomers a mixture of diastereoisomeric rose oxides is thus formed. The unreacted diol isomer is separated by distillation. (—)-Citronellol as the starting material yields approximately a 1 1 mixture of (—)-cis- and (—)-tra s-rose oxide. 

Preparation of Cyclic Sulfites Using 1,2- or 1,3-Diols According to Procedure 2-2... 

Preparation of the Cyclic Sulfite of trans-Cyclohexane-l,2-diol [14]... 

Secondary alkyl sulfites are produced if the formed hydrogen chloride is removed by carrying out the reaction at reduced pressure (aspirator) [9], Examples of the preparation of cyclic sulfites from 1,2-diols are shown in Table II. Other examples involving the preparation of cyclic sulfites are found in a recent patent [20],... 

Likewise, unprotected polyhydroxy compounds can be successfully fluorinated to give the products resulting from substitution of the hydroxy groups by fluorine, wn-o-lnositol reacts with sulfur tetrafluoride and anhydrous hydrogen fluoride at ambient temperature to give a moderate yield of the cyclic sulfite ester of tw/o. cfo-5,6-difluoro-7-oxabicyclo[2.2.1 heptane-e.w,e.vo-2,3-diol (6) and, alter hydrolysis, the free difluoro diol 7.61... 

Dioxathiolane 2-oxides (1,2-diol cyclic sulfites, 21) can be converted to oxiranes (72JOC2589). 

Endosulfan [115-29-7] (36) is the adduct of hexachlorocyclopentadiene and l,4-dihydroxy-2-butene which reacts subsequently with SOCl to produce 6>7>8>9>10>10-hexachloro-l,5,5, 6,9,9 -hexahydro-6>9-methano-2,4,3-benzodioxathiepin-3-oxide. The technical product is a brownish solid (mp 70— 100°C, vp 1.3 mPa at 30°C) which consists of about four parts of a-isomer (mp 108°C, cis with regard to the sulfite group) and one part of the p-isomer (mp 206°C, trans with regard to the sulfite group). The a-isomer, which is somewhat more insecticidal, is slowly converted to the more stable p-isomer at high temperature, and both isomers are oxidized slowly to endosulfan sulfate [1031-07-8] (mp 181°C). In acid media, both isomers form endosulfan diol [2157-19-9] (mp 203°C). The rat LDc-s are 43, 18 (oral) and 130, 74 (dermal) mg/kg. Endosulfan is a broad-spectrum insecticide for vegetables, fruits, and row crops. Unlike the other cyclodiene insecticides, it is biodegradable by hydrolysis at the sulfite ester bonds. 

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],... 

Addition of osmium tetroxide to norbornene 2 followed by reductive cleavage with sodium sulfite gives the exo,exo diol 3. The same reaction sequence carried out on 7,7-dimethylnorbornene 4 gives endo,endo diol 5. From these results deduce the mechanism of the addition and facial selectivity for these two substrates. 

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>. 

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