By the Pummerer rearrangement

All of these ehimnddon reacdons contain fi-carbonyl groups in the nltro compounds Of course, masked carbonyl groups are also frequently employed for such fi-elimination of HNO, as shown in Eq 7131, Eq 7 133, and Eq 7 133In these cases, the sulfinylmethyl or hydroxymethyl group is converted into the carbonyl group by the Pummerer rearrangement or by simple oxidation... 

Thieno[2,3-c]furans have also been prepared in situ by the Pummerer-rearrangement cyclization reaction (96JOC6166). For transient generation of thieno[2,3-c]furans see also Kuroda et al. [91JCS(CC)1635]. These compounds proved to be reactive intermediates for inter- and intramolecular Diels-Alder reactions (see Section IV). 

The first step is just the SN2 displacement of Cl- by RS that you have already seen. The second step actually involves chlorination at sulfur (you have also seen that sulfides are good soft nucleophiles for halogens) to form a sulfonium salt. Now a remarkable thing happens. The chlorine atom is transferred from the sulfur atom to the adjacent carbon atom by the Pummerer rearrangement. 

By the Pummerer rearrangement, jS-oxosulfoxides may be converted under acidic conditions into a-oxoaldehydes (cf. Houben Weyl, Vol. Ell, pp 872-884), and thus be used for cyclizations with orf/io-diamino compounds. Pyridine-3,4-diamines reacting in this way with a-aroylsulfox-ides in the presence of acetic acid give the corresponding 2-arylpyrido[3,4-/)]pyrazines 17.122... 

Aldehydes and alcohols can be generated by the Pummerer rearrangement and many examples exist. For example, Lee et al. employed this reaction in their synthesis of the natural product rolliniastatin 1, among others. The reaction requires the addition of base and proceeds in good yield. 

Abe et al. have reported methodology for the formation of 1,3-oxathiane rings by the Pummerer rearrangement of < -unsaturated sulfinyl... 

Pyrrolo[2,l-c][l,4]benzothiazepine 297 (R=Ph) has been prepared by an intramolecular nucleophilic displacement of acetyl derivative 296 (Scheme 64 (1992H51)). The same compound and its aryl (R = Ar (1992H51)) and carboethoxy or cyano (R = C(30Et or CN (1990H1291)) analogs can also be obtained by a Pummerer rearrangement-cyclization of sulfinyl precursor 298. 

One generally applicable method of oxidation for alkyl bromides involves the Pummerer rearrangement. This gives aldehydes upon rearrangement of the alkyl aryl sulfoxide formed by displacement of halide by thiolate followed by oxidation (equation 41)358. 

The chemical reactivity of sulfoxides as compared with sulfides is much greater. The effect of the sulfinyl group on adjacent methylene protons allows chlorination and the Pummerer rearrangement to take place. The chlorination is stereospecific, resulting in cis products. The Pummerer rearrangement results in two possible isomers (Scheme 2) (55). The Nuphar sulfoxides can be epimerized on carbon C 7 by thermal rearrangement (see Section IV, Scheme 1). 

Thioethers of azines are generally oxidizable to sulfones. By analogy (466) can be oxidized to its sulfone and the intermediate sulfoxide may be isolated. The latter, when subjected to the Pummerer rearrangement, yields the 2-acetoxy derivative (467), which on acid catalysis eliminates acetic acid to form the thiazole (79CPB1207). 

The cyclization of the Pummerer rearrangement product 30 derived from o-methylsulfinyl-difluorostyrene 29 leads to 2-fluorobenzo[ ]thiophene 31 (Scheme 7) <1997CC1537>. Treatment of thiol 32 with NaH affords 2-fluoro-4,5-dihydrothiophene 33 by a cyclization <2000CC1887>. 

A combination of the Pummerer rearrangement and the Ritter reaction occurs in the reaction of acetonitrile with methyl phenyl sulfoxide (equation 25) in a mixture of irifluoroacetic acid and its anhydride, although a substantial amount of the nonnal a-acetoxylation also occurs. Participation by amido groups is also possible, the interest here being largely in the construction of lactams via the intramolecular cycli-zation mode. Whereas Wolfe and his coworkers were unable to find conditions for the cyclization of S-phenylcysteinamide sulfoxides under Pummerer conditions, Kaneko found that variously substituted... 

Among other electrophilic reagents ctq>able of twinging about the Pummerer rearrangement are halides of organic and inorganic acids. As these halides transform sulfoxides into a-chlorosulfides they complement the sulfide chlorination route to these compounds. Thionyl chloride reacts readily with sulfoxides and 3-keto sulfoxides methyl phenyl sulfoxide furnishes chloromethyl phenyl sulfide (equation 37). Benzoyl chloride and acetyl chloride behave similarly. d yanuric chloii is transformed into cyanuric acid by dimethyl sulfoxide, which in turn is transformed into methyl chloromethyl sulfide (equation 3g).54,S5... 

In the examples of the Pummerer rearrangement presented above, the common feature has been the formation of an a-thiocarbocation, which is then captured either intermolecularly or intramolecularly by a nucleophilic species. There are of course other outlets through which the a-thiocarbocation can pro-... 

CcHiimon by-products in these reactions are (methylthio)methyl ethers (3) formed by a Pummerer rearrangement which occurs via an alternative breakdown of (2), as shown in Scheme 3. The proportion of the Pummerer rearrangement derived product varies with the electrophilic activator used. 

---