Plancher rearrangement

Fischer s base, a typical starting material, is commercially available and is also obtained in situ from the corresponding quaternary salt, substituted indolines 4 can be prepared by TV-alkylation of 2,3,3-trimethyl-3//-indole followed by alkali treatment, or by exhaustive alkylation of 2,3-dimethylindole (N- and C-alkylation) followed by alkali treatment (Scheme 3). Further, methylation of indoline 5 with methyl iodide leads to C-methylation on the methylene group or the Plancher rearrange-... 

The derived quaternary salts (e.g. 201) give anhydro compounds (e.g. 202) on treatment with alkali. (3-Pentamethylpyrrolenine (2,3,3,4,5-pentamethylpyrrole) undergoes quantitative conversion to the a-isomer (2,2,3,4,5-pentamethylpyrrole) either on heating (>200°C) or in 1M HC1 at room temperature (71CC1093). Indolenines also undergoes an acid-catalyzed rearrangement (e.g. 203 — 204), known as the Plancher rearrangement. 

A Plancher rearrangement also occurs with an isomer of Fischer s base, as shown in Scheme 5. The addition of methyllithium to 1,2,2-trimethylindoxyl (5) gives l,2,2-trimethyl-3-methyleneindoline (6). This base in acid solution at room... 

The original literature records the preparation of many hundreds of spiropyrans and is the place to look first for a specific compound. Some generalities about the best choice of intermediates and reaction conditions have been given in Section 1.2. Presented here, with an emphasis upon manipulative details, are descriptions of preparations of a typical BIPS on a large laboratory scale (in which the condensation intermediates can be observed) a Fischer s base via a Plancher rearrangement, where the reaction and purification are complex and a salicylaldehyde having a group useful for various further transformations. 

A. A. Tolmachev, L. N. Babichenko, I. V. Komarov, S. V. Sereda, and A. K. Sheinkman, Plancher rearrangement in the reaction of l,3,3-trimethyl-2-cyanomethyleneindoline with ortho-phenylene-... 

The rearrangement of 3,3-diafkyl-3//-indolium ions by alkyl migration to give 2,3-diaUcyl-indoles, as shown in the seqnence above, is related mechanistically to the Wagner-Meerwein rearrangement, and is known as the Plancher rearrangement. It is likely that most instances of 2-alkylation of 3-substituted-indoles by cationic reagents proceed by this route, and this was neatly verified in the formation of... 

Other references related to the Plancher rearrangement are cited in the literature." ... 

Scheme 6.76 Enantioselective synthesis of 1,2,3,4-tetrahydrocarbozole derivatives 163 through AFC alkylation and Ciamician-Plancher rearrangement reported hy Enders.

Eisenbeis and colleagues crafted a collection of azepino[3,4-b]indoles [395] via the so-called Plancher rearrangement, which involves the formation of an indo-lenium ion and then rearrangement to the final indole product (Scheme 56, equation 1) [396-398]. Cho s group reported a novel intramolecular Fischer indolization leading to tricyclic benzo[crf indoles, and a spectacular example is shown in equation 2 [399]. Alford and colleagues used a Fischer indolization to prepare 2,3 -biindoles (equation 3) [400]. 

Parham cycloalkylation 343 Patemo-Btichi reaction 46 von Pechmann synthesis (coumarin) 322 Pellizari synthesis (1,2,4-triazole) 270 Perkin rearrangement 82 Pfitzinger synthesis (quinoline) 398 Pictet-Gams synthesis (isoquinoline) 414 Pictet-Spengler synthesis (isoquinoline) 415 Piloty-Robinson synthesis (pyrrole) 119 Pinner synthesis (pyrimidine) 467 Plancher rearrangement 128 Polonovski reaction 545 Pomeranz-Fritsch synthesis (isoquinoline) 415 Prileschajew reaction 23 Prins reaction 452 Pummerer rearrangement 26, 457... 

Recently, the same group reported a process combining a bifunctional catalyst promoted Friedel-Crafts all lation and Ag-mediated Ciamician-Plancher rearrangement... 

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