Stereoselective reactions 1,5-dioxide

Allyltin bonds are among the most reactive carbon-tin bonds and they undergo reactions with mild electrophiles, e.g. aldehydes (equation 47). Protonolysis of allyltin bonds proceeds with y-regioselectivity and anti stereoselectivity. Sulfur dioxide cleavages, however, occur with y-regioselectivity and... 

Both cis- and fm -2,4-diphenylthietan 1-oxide, (90) and (91), treated separately with potassium t-butoxide in DMF, gave a mixture of cis-, 2-diphenylcyclopropanethiol (92) and cw-l,2-diphenylcyclopropanesulphinic acid (93), which apparently arose by disproportionation of the intermediate sulphenate anion (94) and subsequent protonation. In other highly stereoselective reactions both cis- and /m 5-2,4-diphenylthietan 1,1-dioxide... 

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, which are very useful synthetic intermediates. They react with a variety of electrophiles such as carbon dioxide, epoxides, aldehydes, allylic halides, alkyl halides, and acetylenic halides they undergo... 

Dipolar cycloaddition reaction of benzo(A)thiophene-l,1-dioxide 282 with nonstabilized azomethine ylides gave high overall yield of new pyrrolo derivatives 5 and 6 with low stereoselectivity (Scheme 50) <2006TL5139>. 

The three-component reaction between isatin 432a, a-aminoacids 433 (proline and thioproline) and dipolarophiles in methanol/water medium was carried out by heating at 90 °C to afford the pyrrolidine-2-spiro-3 -(2-oxindoles) 51. The first step of the reaction is the formation of oxazlidinones 448. Loss of carbon dioxide from oxazolidinone proceeds via a stereospecific 1,3-cycloreversion to produce the formation of oxazolidinones almost exclusively with /razw-stereoselectivity. This /f-azomethine ylide undergo 1,3-dipolar cycloaddition with dipolarophiles to yield the pyrrohdinc-2-r/ V -3-(2-oxindolcs) 51. (Scheme 101) <2004EJ0413>. 

The reactions of the resulting stabilized ions 153a,b with silicon dioxide produces isolable polyfunctional compounds 155a,b. It should be emphasized that the configuration of the stereocenters in nitronate (153) remains unchanged in the course of the transformation and the reaction is stereoselective with respect to the new stereocenter at the atom bearing the nitro group. 

Selenium dioxide exhibits a useful stereoselectivity in reactions with trisubstituted gem-dimethyl alkenes. The products are always predominantly the /f-allylic alcohol or unsaturated aldehyde221 ... 

One of the most widely applied cycloaddition techniques for the preparation of thietanes is the reaction of sulfenes with enamines. The stereochemistry of these reactions has been extensively investigated by Truce and Rach. Whether the mechanism is a two-step or a concerted process, both in accordance with the stereoselective formation of the cis form in Scheme 1, is still unresolved. The special orientation of the 1,4-dipolar intermediate 64, in which the charged phenyl and dimethylamino moieties are in proximity, enforces the cis geometry of the resulting thietane dioxide. In the concerted mode of reaction, formation of the orthogonal oriented unsaturated system, 65 should also yield the cis cycloadduct. 

The reaction of Af,Af-dimethyl-( )-styrylamine (73) with a halogen-substituted methanesulfonyl chloride allowed the first stereoselective formation of the halogenated thietane 1,1-dioxide 74, which then could be converted to the corresponding thiete sulfone 75 via a Cope elimination of the corresponding AT-oxide. ... 

The higher homologue of 3-sulfolene, 2,7-dihydrothiepin-l,1-dioxide could be similarly metallated at low temperatures. Reaction with reactive electrophiles followed by extrusion of sulfur dioxide led [549] to the corresponding hexatriene derivatives, as in the stereoselective synthesis of (Z,E)-l,3,5-decatriene (considered as an undecatriene in the publication) shown here. 

There are many pharmaceutical applications for the modification of one enantiomer over another, and to this end, many have studied these selective reactions in carbon dioxide. Glowacz et al. (1996) studied the enzymatic hydrolysis of triolein and its partial glycerides and found that stereoselectivity depends on reaction time and enzyme water content. They suggest that the water content varies the local environment of the enzyme in carbon dioxide and changes the local pH value. Rantakyla et al. (1996) also found that the hydrolysis of one stereoisomer over another was water-dependent. They studied the hydrolysis of 3-(4-methoxyphenyl)glycidic acid methylester and found that the 2S,3R enantiomer hydrolyzed more than fivefold faster than the 2R3S form. 

The stereoselective intramolecular Diels-Alder reaction of 3-alkenyl(oxy)-2(l//)-pyrazinones leading to tricyclic ring systems was investigated <02TL447>. A one-pot 7-alkoxylation of 6-arylpyrazino[2,3-c][l,2,6]thiadiazine 2,2-dioxides 169 was accomplished by using N-halosuccinimides <02EJ02109>, and the nitration of 2-(5-methyl-2-furyl)quinoxaline was shown... 

Several ab initio studies of these reactions including an investigation of Lewis acid catalysis and solvent effects have been published by Sordo et al. [464-466]. Their results concerning regio- and stereoselectivity in the hetero Diels-Alder reactions of sulfur dioxide to isoprene are in good agreement with the experimental findings mentioned above. 

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, 5 which are very useful synthetic Intermediates. They react with a variety of electrophiles such as carbon dioxide,5,6 epoxides,5,6 aldehydes,6 allylic halides,7 alkyl halides,7 and acetylenic halides 7 they undergo conjugate addition to a,6-unsaturated esters,5 6 ketones,6 aldehydes,6 and sulfones.8 Finally they add smoothly to activated triple bonds6 such as HCSC-OEt, HC3C-SEt, HC=C-CH(0Et)2. In most cases these cuprates transfer both alkenyl groups. The uses and applications of the carbocupration reaction have been reviewed recently.9 The configurational purity in the final product 1s at least 99.951 Z in the above transformations. 

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