Pummerer oxidation

The sulfur compounds like 71 can be made by conjugate addition not only to alkynes but also to enones, e.g. 79, by using the Pummerer oxidation of the products 80 with /V-chlorosuccinimide (NCS) 82 to give a (3-thio-enone 81 not accessible by conjugate addition to an alkyne. 

The reaction is quite general and usually results in 75—90% yields (47). All reactions in which a sulfoxide containing at least one a-hydrogen is reduced to the sulfide and also oxidized at the a-carbon ate referred to as Pummerer reactions (48). 

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... 

An alternative approach, which has only been applied to heteroaromatic thiepins, is provided by the Pummerer reaction.70,71 The careful double oxidation of hetarenothicpancs to the corresponding S-oxides, followed by brief treatment with acetic anhydride at 150 °C in the absence of oxygen, gives the heteroaromatic thiepins in moderate yield. 

Due to their thermal instability, this method cannot be applied to the preparation of benzo-thiepins. Although the ft-oxo sulfoxide moiety in precursors such as 5-methoxy-4-phenyl-l-benzothiepin-3(2/7)-one 1-oxide makes them candidates for a Pummerer reaction, treatment with acetic anhydride and triethylamine at - 30 C results in preferential enol acetylation to afford the corresponding 1-benzothiepin 1-oxide.14... 

The tetrahydrotrithiepin 1 is oxidized to an 5-oxide of undetermined structure, which undergoes a Pummerer reaction with acetic anhydride to give 1,2,5-trithiepin (2) in low yield.432... 

Horner and Jurgens39 reported that benzoyl peroxides 21 in the presence of sulphides decompose to give sulphoxides and a-acyloxysulphides 22 (equation 8). The latter compounds are undoubtedly formed as a result of the Pummerer reaction. The oxidation reaction leading to sulphoxides has been shown to be an ionic process40. However, till now it has not found wider synthetic applications. Ganem and coworkers41 showed that 2-hydroperoxyhexafluoro-2-propanol 23 formed in situ from hexafluoroacetone and... 

The Pummerer reaction346 of conformationally rigid 4-aryl-substituted thiane oxides with acetic anhydride was either stereoselective or stereospecific, and the rearrangement is mainly intermolecular, while the rate-determining step appears to be the E2 1,2-elimination of acetic acid from the acetoxysulfonium intermediates formed in the initial acetylation of the sulfoxide. The thermodynamically controlled product is the axial acetoxy isomer, while the kinetically controlled product is the equatorial isomer that is preferentially formed due to the facile access of the acetate to the equatorial position347. The overall mechanism is illustrated in equation 129. 

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. 

Zwanenburg and Wagenaar148 have reported the rather unusual rearrangement of sulfone 81 to 82, after standing overnight at 0°, and suggested an elimination-addition mechanism, via initial isomerization of A3 to the A2-thiazoline-oxide with subsequent elimination and readdition of sulfmic acid, followed by spontaneous loss of water in a Pummerer-type aromatization reaction. 

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... 

Chlorodiphenylphosphine 488 reacts with a-sulphinyl carbanions to give a-sulphinylphosphines 489 which undergo ready isomerization to a-sulphenylphosphine oxides 4W (equation 295). The report of Almog and Weissman that a-sulphinyl carbanions react with phosphorochloridates 491 to give a-phosphoryl sulphoxides 492 calls for correction (equation 296). Actually, the phosphorylation occurs at the oxygen atom of the ambident dimsyl anion, and is followed by the Pummerer-type reaction affording diethylphosphoric acid and tetraethyl pyrophosphate among other products . ... 

A combination of 2,3 sigmatropic rearrangement (Pummerer-type reaction) followed by an electrophilic aromatic substitution of the intermediate sulfenium ion, the formation of an iminium ion and, finally, a second electrophilic aromatic substitution, was used by Daich and coworkers for the synthesis of iso-indolo-isoquinolinones as 4-314 (Scheme 4.68) [106]. Thus, reaction of the two diastereo-meric sulfoxides 4-313, easily obtainable from 4-312 by a Grignard reaction and oxidation, led to 4-314 as a single product after crystallization in 42% yield. 

As depicted in the following scheme, in the presence of sodium iodate and pyridine, several 5,6-dihydroxylated benzofuran derivatives were synthesized via an oxidation-Michael addition of P-dicarbonyl compounds to catechols in a one-pot procedure <06TL2615 06JHC1673>. A novel additive Pummerer reaction of 2-benzo[fc]furan sulfilimines with carbon nucleophiles derived from P-dicarbonyl compounds was also employed to the synthesis of 2,3-disubstituted benzo[b]furans <06TL595>. 

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... 

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