Dimsyl group

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

Trimethylsulfoxonium iodide (11) is of interest because treatment with sodium hydride or dimsyl sodium produces dimethyl sulfoxonium methylide [5367-24-8] (12) (eq. 22), which is an excellent reagent for introducing a methylene group into a variety of stmctures (53) ... 

NaH, /7-MeOQH4CH2Br, DMF, —5°, 1 h, 65%. Other bases, such as BuLi, ° dimsyl potassium," and NaOH under phase-transfer conditions," have been used to introduce the MPM group. The use of (n-Bu)4N I for the in situ preparation of the very reactive p-methoxybenzyl iodide often improves the protection of hindered alcohols." In the following example, selectivity is probably achieved because of the increased acidity of the 2 -hydroxyl group ... 

In strong bases such as the one provided by sodium hydride and dimethyl sulfoxide (DMSO)—namely, dimsyl sodium—one should expect the formation of carbanions at sites of acidic protons. Ketones are attractive as potential sources of carbanions. However, ketone I features two blocked a carbons, without protons. Conversely, the tosyl group is ill suited for carbanion stabilization. The last functionality one may appeal to is the phenyl sulfone substituent at the end of the jec-pentyl chain. Recent investigations have revealed their potential as carbanion precursors, adding an important feature to their considerable usefulness in organic synthesis That is, sulfones can be removed under such mild conditions that carbonyl groups are not affected, and unconstrained a-sulfonyl carbanions have the unusual quality of retaining the asymmetry of their precursors in a wide variety of experimental conditions. ... 

For acylations with reactive esters, such as formate or oxalate (see Section 3.6.4.5), sodium alkoxides are still the bases of choice, but sodium hydride, dimsyl sodium, sodium or potassium amide or sodium metal have all been used for the in situ generation of the enolate anion. A typical example is shown in Scheme 47. Acylation by esters results in the production of 1 equiv. of the alkoxide ion, along with the p-dicarbonyl compound proton transfer then results in the production of the conjugate base of the dicarbonyl compound. This process normally leads to the more stable anion in the acylation of an unsymme-trical ketone. The acyl group thus becomes attached to the less-substituted a-position of the ketone. The less stable 0-acylated products are normally not observed in such reversible base-catalyzed reactions. Methyl alkyl ketones are normally acylated on the methyl group where both a-carbons are substituted to the same extent, acylation occurs at the less-hindered site. Acylation is observed only rarely at a methine carbon as the more stable p-diketone enolate cannot be formed. 

The dimsyl base was seen to be highly effective for the permethylation of P-CD. A moleeular [M+Na] adduct ion was observed at m/z 1451, which corresponds to the molecular mass of P-CD with all of the 21 free hydroxyls replaced by methyl groups (Fig. 2). Except for a single [M-14+Na] at m/z 1437, there was little evidence for partially methylated p-CDs. Moreover, the folly methylated p-CD was also observed as a single band by the TLC analysis (Fig. 2). By contrast, M/LLDI-MS analysis of the NaOH-catalyzed reaction showed a series of ions incrementally 14 mass units less than the folly methylated m/z 1451 molecular ion. This ion series is evidence of a mixture of under-methylated P-CDs. Hence, under-methylated ions are observed at m/z 1437, 1423, 1409, etc. (Fig. 2) where the observed 14 mass unit differentials are due to the mass difference between -H and a -CH3. Furthermore, under-methylated P-CDs formed under the NaOH-catalyzed conditions are also apparent as a less motile ladder when analyzed by TLC (Fig. 2). 

Opening of the dioxolanone ring with dimsyl anion affords jS-ketosulfoxide 213, which is subsequently converted to acetyl derivative 214 by extrusion of sulfur with aluminum amalgam in 90% overall yield. The cyclic boronate 215, with the desired stereochemical configuration at both hydroxyl groups, is formed by treatment of 214 with phenylboronic acid. 

Reaction of the tetrahydrobenzylisoquinoline 5 in the presence of potassium amide and metallic potassium led to the benzazonine 6. On the other hand, when the nucleophilic base dimsyl sodium was employed to effect the cycliza-tion of 5, the products were the indole 7 and the dibenzopyrrocoline tertiary base 8. The migration of the A -methyl group occurs possibly by a Stevens rearrangement. Base 7 was also produced by a similar cyclization of the 3,4-dihydrobenzylisoquinoline 9 (see Scheme 8.1). ... 

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