Sommelet-Hauser rearrangements

Selective o/t/io-acylation and orrfio-formylation of 2-alkyl pyridines is possible by [2,3] sigmatropic rearrangement (Sommelet-Hauser) of a-pyrrolidinyl-2-alkylpyridine sulfonates (268), prepared by treating the parent base with cyanomethyl benzenesulfonate (76JOC2658). Acid hydrolysis of the rearranged product (269 R = H) yields 3-formyl-2-methylpyridine (270). Methylation of (269 R = H) using NaH-Mel and acid hydrolysis of the reaction mixture gives 3-acetyl-2-methylpyridine (270 R = Me). 

Heterocyclic nitrogen-derived ylids behaviors have been studied.373 For instance, pyridine derivatives lead exclusively to [2,3]-sigmatropic rearrangement (Sommelet-Hauser) products. 

The mechanism of the Gassman indole synthesis bears some resemblance to that of the Fischer indole reaction. An Sn2 displacement of the TV-chlorinated aniline with the a-keto sulfide gives rise to a sulfonium ion. After deprotonation, a [2,3]-sigmatropic rearrangement (Sommelet-Hauser rearrangement) takes place where the weak N-S bond is broken and a strong C-C bond is formed. Similar to the Fischer indole reaction, the resulting imine was transformed into indole after re-aromatization and cyclization. 

The Gassman indole synthesis involves a one-pot process in which a hypohalite, a P-carbonyl sulfide derivative, and a base are added sequentially to an anihne or a substituted aniline to provide 3-thioalkoxyindoles. The mechanism of the Gassman indole synthesis involves a [2,3]-sigmatropic rearrangement (Sommelet-Hauser). The sulfur can be easily removed by hydrogenolysis or Raney nickel. 

Methods development for ring contractions generating enediynes H. Audrain etal. Tetrahedron 50,1469 (1994). Review of stereoselectivity K. Mikami, T. Nakai, Synthesis 1994, 594. Reviews J. A. Marshall, Comp. Org. Syn. 3, 975-1014 (1991) T. Nakai, K. Mikami, Org. React. 46,105-209 (1994). Cf. Meisenheimer Rearrangements Mislow-Evans Rearrangement Sommelet-Hauser Rearrangement. 

Another indole/oxindole synthesis achieves the critical ortho-substitution by Sommelet-Hauser rearrangement of an anilinosiilfonium ion intermediate. Use of P-thioketones (G = R, an alkyl group) generates 2-substituted indoles, whereas P-thioesters (G = OR) lead to oxindoles. In each case, a 3-thio substituent must be removed by desulfuri2ation. 

SOMMELET HAUSER Ammonkjmyfld rearrangement Rearrangement of quaternary ammonium ylids to aminas by aryl trarafer. 

The mechanism of the indolization of aniline 5 with methylthio-2-propanone 6 is illustrated below. Aniline 5 reacts with f-BuOCl to provide A-chloroaniline 9. This chloroaniline 9 reacts with sulfide 6 to yield azasulfonium salt 10. Deprotonation of the carbon atom adjacent to the sulfur provides the ylide 11. Intramolecular attack of the nucleophilic portion of the ylide 11 in a Sommelet-Hauser type rearrangement produces 12. Proton transfer and re-aromatization leads to 13 after which intramolecular addition of the amine to the carbonyl function generates the carbinolamine 14. Dehydration of 14 by prototropic rearrangement eventually furnishes the indole 8. 

Benzylic quaternary ammonium salts, when treated with alkali metal amides, undergo a rearrangement called the Sommelet-Hauser rearrangementSince the product is a benzylic tertiary amine, it can be further alkylated and the product again subjected to the rearrangement. This process can be continued around the ring until an ortho position is blocked. ... 

For a method that uses nonbasic conditions, and gives high yields of the Sommelet-Hauser product, with little or no Stevens rearrangement, see Nakano, M. Sato, Y. J. Org. Chem., 1987, 52, 1844 Shirai, N. Sato, Y. J. Org. Chem., 1988, 53, 194. 

Ammonium ylides can isomerize to (1,2) rearrangement products (Stevens rearrangement) or to (2,3) shift products (Sommelet-Hauser sigmatropic rearrangement) when allyl or benzyl are located on the nitrogen atom. A strong microwave effect is noticed (Eq. 66) [116]. 

Transformation of allyl ethers into homoallylic alcohols by treatment with base. Also known as Still-Wittig rearrangement. Cf. Sommelet-Hauser rearrangement... 

An effective method of hexahydrothieno[3,2-c]- and [2,3-c]azocines 146 and 148 syntheses involving a Sommelet-Hauser rearrangement of l,l-dimethyl-2-(2- or 3-thienyl)pyrrolidine salts 145 and 147 under the action of NaNH2 in liquid ammonia has been described (87SC935 Scheme 40). 

The Sommelet-Hauser rearrangement competes when Z is an aryl group (see 3-26). Hofmann elimination competes when one of the R groups contains a 0 hydrogen atom (7-6 and 7-7). 

Rearrangement of benzylic quaternary ammonium salts (Sommelet-Hauser)... 

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