Pummerer-type product

The thiosugar 146 on reaction with ozone followed by treatment with AC2O gave a mixture of three Pummerer-type products 147-149. The sulfoxide of 146 did not yield the Pummerer products 147-149 on treatment with Kc O. Therefore, it has been postulated that these products arise from the ozonide as shown in Scheme 41 <2006JA227>. 

Treating A -aryl-2-(benzylthio)benzamides 342 with [bis(trifluoroacetoxy)iodo]benzene containing TFA resulted in an interrupted Pummerer-type reaction to give 2-aryl-l,2-benzisothiazol-3(2//)-ones 403 through intermediates 401 and 402, rather than the normal Pummerer-type products (Equation 7) <2001H(55)1231>. 

An efficient umpolung reaction by polarity inversion at the jS-position of A-alkoxyenamines has been reported involving the transformation of ketones into a-substituted ketones without isolation of enamine derivatives and intermediate imines the reaction allows a-arylation of ketones under mild conditions. A reaction mechanism has been reported for the reaction of dimethylsulfoxide (DMSO) with (Me3C)2C=C=0 to give a Pummerer-type product (Scheme 53). ... 

A-tosylsulphimides with hydroxide or methoxide in methanol afforded 5-substitution and Pummerer-type products. ... 

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 . ... 

Scheme 2.146. Synthesis of several natural products via Pummerer-type rearrangement/ 1,3-dipolar cycloaddition/ring-opening reactions.

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. 

Methyl carhoxylates.2 The reagent (1) is alkylated by alkyl halides under phase-transfer conditions with NaOH as base. The product is converted to a methyl ester by oxidation followed by a Pummerer-type rearrangement (equation I). 

Oxidation of similarly substituted 3,6-dihydro-27/-selenines 91 with w-chloroperoxybenzoic acid affords the corresponding selenopyrans 92 as well as its 3-chlorobenzoic acid addition product (Equation 38) <1993CC577>. This reaction and that mentioned in Scheme 4 presumably proceed through initial oxidation at selenium followed by a Pummerer-type a-oxidation. Typical yields of the selenopyrans were relatively modest. The effect of base on this reaction was investigated however, it was not clear whether added base was really helpful in improving yields in the reaction. 

Treatment of the isomeric dihydroselenines 93 containing electron-withdrawing groups in both the 2- and 6-positions with w-chloroperbenzoic acid also leads to formation of Pummerer-type oxidation products, the 4H-selenines 94 and the corresponding w-chlorobenzoate ester by-products (Equation 39) <1999J(P1)1155>. The esters could be converted to the corresponding 477-selenines by treatment with polyphosphoric acid trimethylsilyl ester (PPSE), a useful reagent for eliminations under neutral conditions. These 4/7-selenines were key intermediates in the synthesis of selenabenzenes. 

BTI is a useful reagent for Pummerer-type reactions of a-acyl sulphides. Instead of being separately oxidized to their sulphoxides, the sulphides were converted in situ into sulphonium salts these subsequently reacted with added aromatics or intramolecularly to afford various products. These reactions were performed in boiling 1,2-dichloroethane and some results are illustrated in Table 4.6. 

Pummerer-type reaction of a-acetylsulphides with BTI Substrate Product Yield (%)... 

The ease of oxidation depends on the electron availability on the sulfur. In quinoline and pyrimidine analogues of (459) the rate of the reaction is decreased, and in these betaine systems sulfone formation is not observed using peracids in the oxidations. A 2-carboxy group as in (463 R = H) promotes the Pummerer-type rearrangement. The initially formed hemimercaptal mainly eliminates water to give the thiazole (464) a minor product (465) may be formed by ring opening (81H(15)1349). 

Treatment of a selenoether-based carbohydrate derivative with ozone followed by acetic anhydride led to a mixture of Pummerer-type rearrangement products <2006JA227>. 

The reaction involves a Pummerer-type rearrangement to a a-thiocarbocation, which then reacts with the enol silyl ether. The products can be converted by reduction into 1,4-diketones or by oxidation to unsaturated 1,4-diketones. 

Conceivably, the azo-ir system of II could be derived from the internal redox reaction implied in the elimination-addition sequence depicted in the production of III. Subsequent /3 elimination would afford the desired double bond. In the case of nitrogen as the neighboring atom the ylide intermediate of Scheme 26.1 would not be necessary since the availability of a nonbonding pair of electrons should make the use of base accessory. Thus the reaction pathway would be subsequently shortened. Moreover, the required electrophile, thionyl chloride, would be present in the reaction medium in large quantity. The prospect of a Pummerer-type rearrangement during the transformation of I into II is therefore likely. 

Although the reaction of dialkyl phosphites with orthoformic esters has been extended to triethyl trithioorthoformate," the preferred synthesis of formylphosphonate dithioacetals is usually the high-yield Michaelis-Arbuzov reaction of trivalent phosphorus compounds with the appropriate chlo-rodithioacetals.""" For the corresponding hemithioacetals, a Pummerer-type reaction of a-phos-phoryl sulfoxides with alcohols in the presence of iodine is usually the method of choice (Scheme 5.3). " ° However, hemithioacetal formation is solvent dependent and generally gives a moderate yield of product in a mixture with several other byproducts arising from transesterification reactions. 

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