Intramolecular reactions Pummerer rearrangement

An intramolecular version of enolate Michael addition to enantiomerically pure vinylic sulfoxides is represented by reaction of a cyclopentenone sulfoxide with dichloroketene (Scheme 5)90 this type of additive Pummerer rearrangement has been developed by Marino and coworkers91 into a highly effective way of constructing variously substituted lactones in very high enantiomeric purity (equation 43). 

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 ... 

Cycloadditions of dienes with oxyallyl offer the opportunity to prepare seven-membeted ring systems. This reaction has also proved to be of importance in Ae furan series. A few examples may illustrate the value of this methodology. A tandem Pummerer rearrangement and intramolecular [4-i3]-cycloaddition with a fiiran derivative has been reported <99TL545>. For a similar reaction see <99T13999>. 

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). 

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... 

Lactaldehyde 689 has been used as the chiral source in an interesting synthesis of unnatural D-threonine (695) [204] (Scheme 93). The first of the two most important reactions in the sequence is the conversion of 691 to 692. The transformation proceeds by partial methano-lysis of the trichloroacetyl group followed by intramolecular conjugate addition, which forms the oxazolidinone ring in 692 stereospecifically at C-4 and C-5. The second critical reaction is a Pummerer rearrangement of 693 to 694, which introduces the requisite carboxyl function (as... 

The second set of examples involves the use of thionium ions as electrophiles in inter- and intramolecular processes to obtain a-substituted sulfides (see 24 25, Scheme 20.7T which is the most common type of Pummerer reaction. Applications of this classical Pummerer rearrangement are exemplified in the synthesis of trans-solamin, the synthesis of indolizidine alkaloids, and the synthesis of the CDE ring of erinacine E. The first exanple fScheme 20.10 uses Pummerer chemistry in the generation of a thionium ion, which reacts in an intermolecular tin-mediated ene reaction the second one fScheme 20.11 uses Pummerer chemistry to introduce a nitrogen-containing heterocycle by intramolecular addition to form the coniceine core and the third example fScheme 20.12 is an intramolecular silicon-induced Pummerer reaction with oxygenated nucleophiles applied to the synthesis of a precursor of erinacine. Details of these Pummerer-based strategies are discussed below. 

In their studies towards the synthesis of polycyclic natural products such as pseudolaric acid A, Bai et al. reported the tandem Pummerer rearrangement and intramolecular [4 + 3] cycloaddition of sulfoxide 104." The reaction constitutes the overall [4 + 3] cycloaddition of a fully... 

Pummerer Rearrangement. When a 5-hydroxysulfoxide is treated with TBDPS-Cl and imidazole in DMF, the sulfoxide oxygen coordinates with the TBDPS silicon atom to form the sulfoxonium salt, which further converts into the corresponding sulfonium ion and eliminates a molecule of TBDPS-OH. Intramolecular attack by the 5-hydroxy group furnishes the substituted THF as the sole product in excellent yield (eq 14). In contrast, when the same 5-hydroxysulfoxide is treated with TBDMS-Cl, the reaction offers a mixture of both the rearrangement product and the corresponding TBDMS silyl ether in 2 1 ratio. 

During the studies shown in Scheme 20.31. the authors noticed that, in some cases, the spirocyclic system was not the reaction product Instead, they obtained a rearranged conpound 172, probably resulting from an intramolecular aryl transfer as shown in Scheme 20..3.3. This transformation, initiated by Pummerer chemistry provides a new synthesis of a-arylacetamides, which are present in a large number of active molecules. ... 

As an extention of this reaction, the reagent promotes the intramolecular Pummerer-type rearrangement of ffl-carbamoyl... 

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