Sigmatropic rearrangement sequence

Scheme 3.56 Allyl sulfides imination/sigmatropic rearrangement sequence.

This is a classic Claisen [3,3]-sigmatropic rearrangement sequence starting with an allylic alcohol This product was used in a ind forming a vinyl ether by acetal (or in this case, orf/ioester) exchange. The reaction is very trans- synthesis of chrysanthemic acid by... 

The first total synthesis of (+)-agelastatin A was achieved by Weinreb and coworkers in 1999. Their approach (Scheme 5) revolved around the use of a hetero-Diels-Alder /[2,3]-sigmatropic rearrangement sequence to... 

Scheme 14.37 Domino Sonogashira/lactonization/sigmatropic rearrangement sequence by Parrain and Chouraqui for the synthesis of the ABCD skeleton of natural products of the Schisandraceae family.

Scheme 20.29 Applications of interrupted Pummerer reaction - r3.31-sigmatropic rearrangement sequence.

Scheme 20.29 exemplifies four different approaches to carry out an interrupted Pummerer reaction [3,3]-sigmatropic rearrangement sequence. Oshima s work use phenol 138 as nucleophile generating the optimal intermediate 140 for the sigmatropic rearrangement the formed product 141 can rearrange to afford... 

The absolute configuration of phyUanthidine (6) was proposed on the basis of the stereochemical outcome of the oxidation reaction of allosecur-inine. This transformation passes through a [2,3]-Meisenheimer/[l,3]-sigmatropic rearrangement sequence, and the geometry of the end product... 

Weinreb and co-workers contributed to showcase the synthetic utility of this reaction with the total syntheses of the freshwater cyanobacterial hepatotoxins cylindrosper-mopsins, which featured a sulfinyl Diels-Alder reaction/ allylic sulfoxide [2, 3]-sigmatropic rearrangement sequence to form the i yn,jy -7-hydroxy-8,10-diamino centers of... 

Gassman and co-workers developed a synthetic route from anilines to indoles and oxindoles which involves [2.3]-sigmatropic rearrangement of anilinosul-fonium ylides. These can be prepared from Ai-chloroanilines and ot-thiomcthyl-ketones or from an aniline and a chlorosulfonium salt[l]. The latter sequence is preferable for anilines with ER substituents. Rearrangement and cyclizalion occurs on treatment of the anilinosulfonium salts with EtjN. The initial cyclization product is a 3-(methylthio)indole and these can be desulfurized with Raney nickel. Use of 2-(methylthio)acetaldehyde generates 2,3-unsubstituled indoles after desulfurization[2]. Treatment of 3-methylthioindoles with tri-fiuoroacetic acid/thiosalieylie acid is a possible alternative to Raney nickel for desulfurization[3]. 

Another version of the double [2,3]-sigmatropic rearrangement, involving the sequence sulfenate - sulfoxide - sulfenate, has also been observed. For example, an effective one-pot epimerization procedure of 17a-vinyl-l 7/i-hydroxysteroids to the rather inaccessible 17-epimers has been achieved by the use of such a rearrangement (equation 35)137. Thus treatment of alcohol 76a with benzenesulfenyl chloride afforded the sulfoxide 77 as a single isomer and E-geometry of the olefinic double bond. Exposure of 77 to trimethyl phosphite in refluxing methanol produced a mixture of 76b and 76a in a 73 27 ratio. 

The thiol 48 (with R R, R = H) undergoes intramolecular cychsation in THF, in the presence of AIBN under UV irradiation, to give a 2-phosphonothiolane [36], a phosphorus and sulfur analogue of proline. More recently, an asymmetric version of the sequence, [2,3]-sigmatropic rearrangement and radical cychsation, has been carried out (see Sect. 5.1.1.) [41]. 

Among all tandem hydroformylation sequences the ones involving additional C,C-bond formations are the most synthetically valuable tandem hydroformylation sequences. These C,C-bonds can be formed by adding nucleophiles, which attack the carbonyl carbon, or by adding electrophiles, which attack the a-position. Furthermore, tandem reactions in which the aldehyde or an aldehyde derivative is involved in sigmatropic rearrangement are described. 

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