Pummerer rearrangement halides

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]. 

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 ... 

A highly stereoselective vinylogous Pummerer rearrangement of a optically active sulfoxide has been shown to proceed by a [l,4]-migration of the sulfinyl oxygen atom via an intermediate intimate ion pair (Scheme 12).16 The reaction occurs with high enantioselectivity when o-sulfinyl-substituted benzyl carbanions are treated with trimethylsilyl halides. 

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. 

Ketone synthesis. The intermediate a in the synthesis of aldehydes can be alkylated in the presence of TMEDA to give the ketone equivalent 2. The silanes are converted into ketones (3) by a sila-Pummerer rearrangement (10, 314). Unfortunately, only primary alkyl halides give satisfactory yields. 

Electrc hilic reagents capable of Mnging about Pummerer rearrangement include inoiganic and organic acids, carboxylic anhydrides, acyl halides, isocyanates, caibodiimides, irimethylsilyl halides and triflate, sulfonyl and sulfenyl halides, phosphorus pentoxide and many typical Lewis acids such as boron... 

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... 

The use of trimethylsilyl halides has been expanded further to afford optically pure benzyl alcohols through a stereoselective vinylogous Pummerer rearrangement. The reaction proceeds via a l,4 migration of the sufinyl oxygen atom to give (i )-benzyl alcohols 30a-f with > 98% ee. 

The reagent (1) also reacts with wide variety of eiectrophiies, including carbon dioxide, cyanogen, siiyi chiorides, metal halides, and phosphorus(III) chloride With methyl phenyl sulfinate, reaction of (1) leads to the formation of (phenylthio) (trimethylsiloxy)methane, a protected form of formaldehyde, by a sila-Pummerer rearrangement. ... 

The reactions of sulphimides studied recently concern the kinetics of the reaction between PhSH and JV-toluene-p-sulphonyl-sulphimides - to give PhSSPh, or RSPh (other differences exist between the results from these two studies) the formation of vinyl sulphides by treatment of JV-toluene-p-sulphonyl aryl ethyl sulphimides with Bu OK [TsN=S(Et)Ar -> CHg= CHSAr] the halide-ion-induced Stevens-type rearrangement to the sulphen-amide [TsN=SRAr -> RN(Ts)SAr] and the S-substitution or Pummerer rearrangement products from iV-toluene-/j-sulphonyl-sulphimides by cleavage with NaOH or NaOMe in MeOH. °... 

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). 

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