Substituent rearrangement

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]. 

Special reactions of side-chain substituents rearrangements involving three-atom side chains... 

The interaction between thiophenes and oxocarbenoids, in general, leads to sulfur ylides 42 as the initial products. Depending on the substituents R R, R and the temperature, these ylides can be isolated (R, R carbanion-stabilizing substituents), rearrange to a 1,4-oxathiocin (2,5-dichlorothiophene and ethyl 2-diazo-3-oxobutanoate ° ) or to 6-acyl-2-thiabicyclo[3.1.0]hex-3-enes, 2-acyl-2//-thiopyrans or 2-acylmethylthiophenes. Theoretical calculations and experimental results suggest intermediate 43 as the common precursor for the latter three products. 

In the HP-SbP, system the O-alkyl group of alkyl aryl ethers bearing p-alkyl or 2,6-dialkyl substituents rearranges to the meta position of the aromatic nucleus (Scheme 14,18) [45], Diprotonation of para-substituted phenols with I IP-Sbly occurs at the oxygen and meta carbon atoms, and the resulting diprotonated species undergo Friedel-Crafts alkylation with arenes [46],... 

Ammonolysis of aromatic halides, however, may lead to unexpected products. For example, Gilman and Martin report that aryl ethers, thio ethers, and sulfones with ortho-halogen substituents rearrange to metarsubstituted anilines when treated with sodamide in liquid NH3. 

There are two properties of cations that must be considered before considering their reaction with a nucleophilic species regioselectivity in formation of the cation and migration of substituents (rearrangement). The first is easily dealt with. In general, the more stable cation is formed. Since 3 is essentially a carbon with an empty p orbital, electrons from the adjacent bonds will be attracted to that positive center (inductive effect). 

Certain cobalt cyclobutadiene complexes with acetylenic substituents rearrange on vacuum distillation through a hot tube (525 °C) and two mechanisms have been considered. The one in Scheme 15 involves a [2+2] cycloaddition so that... 

N-Aryl ketenimines bearing cyclic acetal functions at the ortho position of the N-aryl substituent rearrange thermally into quinolines, through a tandem sequence consisting of a [1,5]-H shift followed by a 67t electrocyclic ring closure (Scheme 28). ... 

It often is assumed that this type of toluene-cycloheptatriene rearrangement applies to other polysubstituted alkylbenzenes, alkylarenes and even alkyl heteroarenes. Indeed, this rearrangement explains the abundant loss of a whole substituent from an arene molecular ion in spite of the normally strong bond to a C(sp ) atom of the arene, which has to be cleaved to detach the substituent. Rearrangement into a substituted cycloheptatriene radical... 

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