Pummerer rearrangement oxidation

A review of the scope and limitations of fluoro-Pummerer rearrangements, oxidative desulfiirization-fluorination, and oxidative desulfurization-di- and tri-fluorination reactions for the synthesis of fluorinated compounds has been reported. ... 

Sharpless and Masumune have applied the AE reaction on chiral allylic alcohols to prepare all 8 of the L-hexoses. ° AE reaction on allylic alcohol 52 provides the epoxy alcohol 53 in 92% yield and in >95% ee. Base catalyze Payne rearrangement followed by ring opening with phenyl thiolate provides diol 54. Protection of the diol is followed by oxidation of the sulfide to the sulfoxide via m-CPBA, Pummerer rearrangement to give the gm-acetoxy sulfide intermediate and finally reduction using Dibal to yield the desired aldehyde 56. Homer-Emmons olefination followed by reduction sets up the second substrate for the AE reaction. The AE reaction on optically active 57 is reagent... 

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... 

Chlorotrimethylsilane-induced Pummerer rearrangements effect the transformation of 4-ketothiane oxides into the corresponding a, /1-unsaturated thianes348, apparently via the formation and subsequent deprotonation of thiiranium intermediates rather than by the conventional sulfocarbonium mechanism depicted in equation 129. 

Prostaglandins 624, 725, 960 Prostanoids 620 Protonation 565-567, 1049 photochemical 882 Pseudopotential methods 15, 16 Pummerer rearrangement 240, 243, 470, 843 Pyramidal inversion 602, 604 Pyrazolenines 749 Pyridazine oxides 640 Pyridine aldehydes, synthesis of 310 Pyridine oxides 640 Pyrolysis 102-105 of sulphones 110, 679-682, 962 of sulphoxides 739, 740 Pyrroles 265, 744... 

The differing nucleophilicity of acetate and trifluoroacetate anion determines the direction in which naphtho[l,8-b,c]-l,5-dithiocine-l-oxide 59 rearranges on treatment with acetic and trifluoroacetic anhydrides. In both cases the reaction proceeds through formation of a disulfonium dication, but the final products are different. When acetic anhydride is used, the reaction affords the corresponding a-acetylsulfide 60 - a normal product of the Pummerer rearrangement, while trifluoroacetic anhydride causes isomerization with formation of dithioacetal 61 (Scheme 22).87... 

Phenylthio-l-trimethylsilylalkanes are easily prepared by the alkylation of (phenylthioXtrimethylsilyl)mcthane as shown in Scheme 10 [40], The treatment of (phenylthio)(trimethylsilyl)methane with butyllithium/tetramethylethylene-diamine (TMEDA) in hexane followed by the addition of alkyl halides or epoxides produces alkylation products which can be oxidized electrochemically to yield the acetals. Since acetals are readily hydrolyzed to aldehydes, (phenylthioXtrimethylsilyl)methane provides a synthon of the formyl anion. This is an alternative to the oxidative transformation of a-thiosilanes to aldehydes via Sila-Pummerer rearrangement under application of MCPBA as oxidant [40, 41]. 

Complexation of sodium to the persulfoxide A (Fig. 13B) appears to inhibit intramolecular hydrogen abstraction to form the hydroperoxy sulfonium ylide (B in Fig. 13A) and allows a direct reaction of 12 with the sodium-complexed persulfoxide, (A in Fig. 13B) to compete. Consistent with this suggestion is the observation that the formation of 13CHO that emanates from the hydroperoxy sulfonium ylide by Pummerer rearrangement and subsequent cleavage is completely suppressed during photo-oxidations of thiolane, 13, in NaMBY ... 

Further elaboration of the sulfur cycloadducts could be achieved by the use of a Pummerer rearrangement in the syntheses of 5-(hydroxymethyl)prolines. Oxidation of adduct 298 to sulfoxide 299, followed by treatment with TEA in DCM and quenching with either methanol or benzyl alcohol, delivered the Pummerer products 300 in 57% yield for R = Me and 38% for R = Bn as single diastereoisomers. Raney Ni desulfurization and Pearlman s catalyst mediated hydrogenolysis, for R = Bn furnished the final enantiopure proline derivative (Scheme 3.99). 

Formaldehyde anion synthon ( CHO). The anion of 1 (n-BuLi, THF, 0°) is readily alkylated, particularly by primary halides. The products can he converted into aldehydes under very mild conditions. Oxidation with m-chloroperbenzoic acid gives an unstable sulfoxide, which undergoes an sila-Pummerer rearrangement to an acetal. Addition of water liberates the free aldehyde. Epoxides can also be used as electrophiles.2 3 Example ... 

The best available methods for synthesis of the parent heterocycles are clearly (a) Pummerer rearrangement of thiane 1-oxide, followed by elimination, affording the 3,4-dihydro compound and (b) dehydration of thian-4-ol to give the 3,6-dihydro system (78JHC289). Preparation of the benzannelated compounds is covered in reviews (75AHC(18)59, 80AHC(26)115>. 

New examples of application appear regularly. In the following one [248] phenylsulfenylation of nopinone (4) was followed by oxidation to the sulfoxide. Pummerer rearrangement of the latter led directly to the a-phenylthio substituted a-unsaturated ketone (6) (overall yield 94%), starting material for further elaboration of natural sesquiterpene synthesis via 4,4-disubstituted nopinones (7). 

This form of activated DMSO is stable below —30°C, but suffer a Pummerer rearrangement above this temperature, resulting in the formation of methylthio-methyl trifluoroacetate (23). In fact, compound 23 reacts with alcohols in the presence of an amine, resulting in a very quick trifluoroacetylation. However, this trifluoroacetylation pathway is not operative in a properly perfonned Omura-Sharma-Swem oxidation, because alcohols are previously transfonned in afkoxy-dimethylsulfonium salts 24. 

Oxidation of 1,2,5-trithiepine 44 with ///-chloroperoxybenzoic acid in CHCI3 resulted in the formation of crystalline monosulfoxide 130, which underwent Pummerer rearrangement upon reaction with acetic anhydride to furnish 6,7-dihydro[l,2,5]trithiepin 45 (Scheme 31) <1997JOC2432>. 

Pummerer rearrangement of this sulfoxide in acetic anhydride under reflux furnished 3,4-dihydrothiepin 45. The trithiepine 46 was obtained upon oxidation and Pummerer rearrangement of 3,4-dihydrothiepine. Alternatively, 3,4-dihydrothiepine was also obtained by the reaction of 1,2,5-trithiepine with A-chlorosuccinimide, followed by treatment with EtjN <1997JOC2432>. 

Pummerer cyclization. Pummerer rearrangement of 4-(phenylsulfinyl)butyric acids (1) catalyzed by TsOH results in 4-phenylthio-4-butanolides (2). Oxidation followed by thermolysis results in either 3 or 4, depending on the substitution pattern. 

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