Indoles rearrangements give

The final, critical oxidative spirocyclization of the 2,3-disubstituted indole to the spiro oxindole was effected by treatment of 124 with tert-butyl hypochlorite in pyridine to provide the labile 125 [Fig. (34)]. The Pinacol-type rearrangement was conducted by treating compound 125 with p-toluenesulfonic acid in THF/water. It is assumed that the chlorination of 124 proceeds from the least hindered face of the indole, to give the a-chloroindolene 125. The hydration of the imine functionality must also occur from the same a-face that is syn to the relatively large chlorine atom furnishing the syn-chlorohydrin 126, that subsequently rearranges stereospecifically to the desired spiro oxindole 127. 

Although there appear to be no examples of the specific acid-catalyzed rearrangement of 3-substituted indoles to give the 2-substituted indoles, electrophilic substitution of 3-substituted indoles is known to proceed via the attack at the 3-position to give the... 

A 1-vinylamino-indole undergoes a 3,3-sigmatropic rearrangement giving the tricyclic ring system of the eseroline alkaloids " ... 

Another hitherto unobserved type of rearrangement which may have synthetic and biogenetic implications has been found by Casnati et al. (77). 3-Alkyl-l-allyl-indoles rearrange under acid catalysis by trifluoro-acetic acid to give 2-allyl derivatives. A 3-protonated species seems to be the most probable intermediate for this new type of rearrangement, which was clearly shown to occur intramolecularly. 

Reaction of indole with excess of methyl iodide at 110°C gives a tetramethyl derivative (66). The intermediate 2,3-dimethylindole (65) is thought to arise by rearrangement of the 3,3-dimethyl-3Ff-indolium cation (64). 

The enamine-imine tautomerism of the indolenine system gives rise to rearrangement reactions of interest in indole alkaloid chemistry. Thus the synthesis of dihydroburnamicine (625) utilized the rearrangement of an acetoxyindolenine to an a-hydroxyalkyl indole, presumably through an intermediate enamine. Similarly 2,3-dialkyl indoles undergo oxidations to 2-acyl indoles (626-631). 

Pd2(dba)3/l,4-bis(diphenylphosphino)butane (DPPB) in the presence of 2-mercaptobenzoic acid <95TL1267>. The Af-allylindolines can be easily oxidized to the corresponding indoles at room temperature with o-chloranil. Additionally, Al-allylanilines were also found to undergo aromatic 3-aza-Cope rearrangements in the presence of Zeolite catalysts to give indoline derivatives as the major product <96TL5281>. 

As shown in Scheme 4.3, the Fisher indolization was thought to involve (i) hydrolysis of diethyl dimethylamino acetal 11, (ii) formation ofhydrazone 22, (iii) isomerization ofhydrazone to me-hydrazine 23, and (iv) [3.3] sigmatropic rearrangement followed by ring closure to give indole 16b. Acetal 11 is stable in AcOH at room temperature, but can be readily hydrolyzed to aldehyde 19 at 100 °C, with subsequent cyclization to hemiaminal 20. Hemiaminal 20 was also formed readily... 

MgS04, the tetracycles 2-648 were obtained with excellent diastereoselectivity in reasonable yield. The reaction presumably starts with a condensation of the aldehydes 2-645 with the benzyl-protected amine moiety of 2-644 to give an iminium ion which can subsequently cyclize to afford the spirocyclic intermediates 2-646. A [3,3] sigmatropic Cope rearrangement then forms the nine-membered cyclic enamines 2-647 which, after protonation, act as the starting point for another indole iminium cyclization to provide the tetracycles 2-648 via 2-647. 

The pyrido[3, 4 4,5]furo[3,2-A]indole 24 can be prepared by Curtius rearrangement of 3-[5-(2-nitrophenyl)-2-furyl]-propenoic azide 25, followed by reduction of the nitrophenyl functionality of the product 26, chlorination of the tetracyclic product (PCI5), then reduction (Zn/AcOH) to give the parent compound 24 <1987CCC192> (Scheme 7). 

Acylation of the tryptamine-based /3-enamino esters 458 with acryloyl chloride and its derivatives results in acylation of the enamine nitrogen and formation of the pyridiniminium ion intermediate 459. Electrophilic attack at C-3 of the indole and rearrangement of the spiro intermediate gives the indoloquinolizines 460 (Scheme 102) <2003TL6527>. 

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