In the Pummerer rearrangements

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... 

Recently, the Pummerer rearrangement has been employed also in the 2//-selenopyran synthesis (93CC577). 

The differing nucleophilicity of acetate and trifluoroacetate anion determined the manner in which naphtho[l,8-/yt]-l,5-dithiocinc sulfoxide 127 rearranged on treatment with acetic and trifluoroacetic anhydrides. In both cases, the reaction proceeded through formation of a disulfonium dication 128, but the final products were different. When acetic anhydride was used, the reaction afforded the corresponding a-acetylsulfide 130, a normal product of the Pummerer rearrangement, while trifluoroacetic anhydride caused isomerization with formation of dithioacetal 132 (see Scheme 16) <1995HAC559>. 

Monosulfoxide 13 undergoes the Pummerer rearrangement when treated with acetic anhydride in the presence of sodium acetate.85 The experiments with tetradeuterated and 180-labeled sulfoxide confirm intermediate formation of a dication.86 The ratio of 2,8,8-trideuteriated to 4,4,6,6-tetradeuteriated product 37 is equal to the intramolecular isotope effect ku k0 =1.7 (Scheme 21).85... 

Reaction of -dimethylthiobenzene sulfoxide 56 with trifluoroacetic anhydride results in a mixture of sulfide 65 and the corresponding mono- and disubstituted products of the Pummerer rearrangement 63, 64 via intermediate disulfonium dication 62 (Scheme 23).88... 

Recently, new examples of asymmetric induction in the Pummerer reaction of chiral sulfoxides have been described. Oae and Numata (301) reported that the optically active a-cyanomethyl p-tolyl sulfoxide 275 undergoes a typical Pummerer rearrangement upon heating with excess of acetic anhydride at 120°C, to give the optically active a-acetoxy sulfide 276. The optical purity at the chiral a-carbon center in 276, determined by means of H- NMR spectroscopy using a chiral shift reagent, was 29.8%. 

Can the organic chemists associated with so-called Named Reactions make the same claim as supermodel Heidi Klum Many scholars of chemistry do not hesitate to point out that the names associated with name reactions are often not the acmal inventors. For instance, the Arndt-Eistert reaction has nothing to do with either Arndt or Eistert, Pummerer did not discover the Pummerer rearrangement, and even the famous Birch reduction owes its initial discovery to someone named Charles Wooster (first reported in a DuPont patent). The list goes on and on... 

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 Pummerer rearrangement has also been used to transform the 4-tolylsulfinyl group, which is an effective chiral auxiliary, into other functionalities via the aldehyde. Thus, chiral /> -(ben-7yloxy)-/J-(fluoroalkyl) sulfoxides 11 have been transformed into aldehydes 12 in a two-step process.7,8 The 3,3-difluoro-substituted aldehydes 12 can be converted directly into a variety of other functional groups without isolation. The chiral center at C2 is derived from the corresponding chiral / -oxo sulfoxide, which can be reduced diastereoselectively due to the presence of the chiral 4-tolylsulfinyl group.7,8 Diastereoselective reduction of fluorine-free fi-oxo sulfoxides has been intensively studied, especially in the laboratories of Solladie.9... 

Methods for the construction of the thieno[2,3-c]pyridine skeleton based on the formally simultaneous formation of both the pyridine and thiophene rings were documented. Under the Pummerer rearrangement conditions, ( -s ul liny lain idc 222 underwent a cascade transformation into 223, which was oxidized to fused lactam 224 in low yield (1999JOC2038). Data on the use of cascade transformations, including the Pummerer rearrangement - cycloaddition sequence, in the synthesis of complex heterocyclic systems were summarized in a review (1997S1353). 

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). 

As previously described, the effect of substituent groups on the silyi function is an important factor in terms of determining the reaction course. Table 4 shows the ratio of the products in the Pummerer reaction using various SKAs.33 These results suggest that carbon-carbon bond formation preferentially occurs when using a small silyi function such as the trimethylsilyl function. This tendency was observed in another substrate which has asymmetric carbon at the (3-position of the sulfur atom (Table 5).33 Interestingly, the syn-selectivity of the rearrangement product... 

Asymmetric Pummerer rearrangement is a very attractive reaction as previously described. In particular, the reactions induced by SKA work well, and may be synthetically exploited in many cases. The results described here demonstrate that the stereoselective a-deprotonation of the sulfoxide is a prerequisite process for asymmetric induction in the Pummerer reaction. Since many kinds of synthetic and enzymatic preparative methods of optically pure sulfoxides have been developed, the present Pummerer-type reaction will be applicable to many other chiral sulfoxides with one a-substituent, chiral vinylsulfoxides and chiral co-carbamoylsulfox-ides, thus leading to enantioselective syntheses of many new bioactive compounds in the near future. 

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... 

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