Tryptamine reaction

Tetrahydroharman, m.p. 179-80°, has been prepared by a number of workers by a modification of this reaction, viz., by the interaction of tryptamine (3-)5-aminoethylindole) with acetaldehyde or paraldehyde and Hahn et al. have obtained a series of derivatives of tetrahydronorharman by the use of other aldehydes and a-ketonic acids under biological conditions of pH and temperature, while Asahina and Osada, by the action of aromatic acid chlorides on the same amine, have prepared a series of amides from which the corresponding substituted dihydronorharmans have been made by effecting ring closure with phosphorus pentoxide in xylene solution. 

Marazano and co-workers have also applied the reactions of tryptamine with various Zincke salts, including 115 (Scheme 8.4.39), in the synthesis of pyridinium salts such as 116. This type of product is useful for further conversion to dihydropyridine or 2-pyridone derivatives. For example, in a different study, Zincke-derived chiral pyridinium salts could be oxidized site-selectively with potassium ferricyanide under basic conditions as a means of chiral 2-pyridone synthesis (117 —> 118, Scheme 8.4.40). 

The Bischler-Napieralski reaction involves the cyclization of phenethyl amides 1 in the presence of dehydrating agents such as P2O5 or POCI3 to afford 3,4-dihydroisoquinoline products 2. This reaction is one of the most commonly employed and versatile methods for the synthesis of the isoquinoline ring system, which is found in a large number of alkaloid natural products. The Bischler-Napieralski reaction is also frequently used for the conversion of N-acyl tryptamine derivatives 3 into p-carbolines 4 (eq 2). 

Bischler-Napieralski reactions of N-acyl tryptamine derivatives 16 are believed to proceed via a related mechanism involving the initial formation of intermediate spiroindolenines (17) that rearrange to the observed 2-carboline products (18). The presence of these intermediates has been inferred by the observation of dimerized products that are presumably formed by the intermolecular trapping of the spiroindolenine by unreacted indole present in the reaction mixture." ... 

Ganellin and Ridley subsequently showed that this reaction was of wide applicability and could be applied to the synthesis of tryptamine (23) itself and a number of indole derivatives with 3-(S-mono- or 3- -dialkylaminoalkyl side chains where the side chain contained two or more carbon atoms.A number of compounds of this general type including 79, 80, 81, 82, 83, 84, 85, and 86 have been prepared by these authors. Trace quantities of the corresponding l-(/8-dialkylaminoethyl)indole derivatives were formed atthe same time as other isomers. However, only the A-substituted product. 

One instance of an intramolecular Mannich reaction of an A -acyl-tryptamine has been reported. ... 

The reactions of tryptophan and of tryptamine derivatives with formaldehyde require special comment. Whereas tryptamine and its 5- and 7-methoxy and i id-A-methyl and -ethyl derivatives react... 

Reaction of tryptamine with simple ketones has not been widely explored. Acetone in the presence of benzoyl chloride has been reported to yield 2-benzoyl-1,1 -dimethyl-1,2,3,4-tetrahydro-j8-carbo-line. That the keto group is much less reactive than the aldehyde group is indicated by the fact that j8-keto aldehydes, in the form of their acetals or sodium salts, react with tryptamine at the aldehyde function to yield the conjugated enamine 24, which undergoes ring closure via an intramolecular Michael addition. The potentialities of this interesting modification of the Pictet-Spengler reaction have not yet been fuUy explored. 

The reaction of tryptamine with a-oxo acids on the other hand has been extensively investigated by Hahn and his co-workers and... 

Amides, prepared by condensation of tryptamine or substituted tryptamines with a large number of aliphatic, homocyclic, aromatic,and heterocyclic acids, have been used in the reaction. In few cases only did ring closure fail. ... 

The most recent method is a Mannich reaction of tryptamine, formaldehyde, and the j8-keto ester 119, which yields the desired lactam 118 in one step. ... 

The second line of circumstantial evidence quoted in support of this hypothesis is the ready formation of l,2,3,4-tetrahydro-/3-carboline derivatives under pseudo-physiological conditions of temperature, pH, and concentration. Tryptamine and aldehydes, trypt-amine and a-keto acids, and tryptophan and aldehydes condense at room temperature in a Pictet-Spengler type intramolecular Mannich reaction in the pH range 5.2-8.0 (cf. Section III, A, 1, a). It was argued that experiments of this type serve as models for biochemical reactions and may be used in evidence. 

Michael addition reaction of 1-hydroxytryptamines to Q ,/3-unsaturated carbonyl compounds is worthy of note (99H2815). Addition of Ab-acetyl- 1-hydroxy-tryptamine (39) to methyl acrylate and methyl crotonate in the presence of... 

Treatment of 1-hydroxy-iVb-trifluoroacetyltryptamine (48), which is readily available in three steps from tryptamine (259, Scheme 40), with MsCl in THF in the presence of indole (3 mol eq) and EtsN produces l-trifluoroacetyl-1,2,3,8-tetrahydropyrrolo[2,3-(j]indole (49c, 25%), l-trifluoroacetyl-3a-(4-chlorobutoxy)-l,2,3,3a,8,8a-hexahydropyrrolo[2,3-(j]indole (52c, 6%), iVb-trifluoroacetyl-6-mesyloxytryptamine (50c, 8%), 3a-(indol-2-yl)- (260, 5%), and 3a-(indol-3-yl)-l-trifluoroacetyl-l,2,3,3a,8,8a-hexahydropyrrolo[2,3-(j]indole (261, 12%). In this reaction, solvent plays an important role. Among the tested solvents such as benzene, CHCI3, 1,2-dichloroethane, THF, DMF, CH3CN, and iV-methylformamide, CHCI3 is found to be the solvent of choice to provide a 21% yield of 261. The use of excess indole (10 mol eq) further raises the yield to 30%. 

Dimerization is also prevented by the presence of a formal positive charge on a j8-substituent, thus tryptamine cannot be dimerized. The formation of the trimer can be rationalized by analogy with the reactions of gramine and its derivatives. Thus, Thesing and Mayer found that methylphenylskatylamine (49) reacts with... 

The reaction of 5-methoxy-2(5//)-furanone 168 with amines was also studied (89T6799). The conjugated addition of ethanolamine to the furanone 168 gave the racemic amino lactone 275 (R = CH2CH20H). Similarly, piperazine reacted with two equivalents of 168 to provide the diadduct 276 as a single diastereomer (no traces of the other isomer were detected). With tryptamine, the reaction was nearly quantitative with the the formation the tran -adduct 277 (R = tryptophanyl) (Scheme 72) (89T6799). 

Woodward s strychnine synthesis commences with a Fischer indole synthesis using phenylhydrazine (24) and acetoveratrone (25) as starting materials (see Scheme 2). In the presence of polyphosphor-ic acid, intermediates 24 and 25 combine to afford 2-veratrylindole (23) through the reaction processes illustrated in Scheme 2. With its a position suitably masked, 2-veratrylindole (23) reacts smoothly at the ft position with the Schiff base derived from the action of dimethylamine on formaldehyde to give intermediate 22 in 92% yield. TV-Methylation of the dimethylamino substituent in 22 with methyl iodide, followed by exposure of the resultant quaternary ammonium iodide to sodium cyanide in DMF, provides nitrile 26 in an overall yield of 97%. Condensation of 2-veratryl-tryptamine (20), the product of a lithium aluminum hydride reduction of nitrile 26, with ethyl glyoxylate (21) furnishes Schiff base 19 in a yield of 92%. 

The Pictet-Spengler reaction has mainly been investigated as a potential source of polycyclic heterocycles for combinatorial apphcations or in natural product synthesis [149]. Tryptophan or differently substituted tryptamines are the preferred substrates in a cyclocondensation that involves also aldehydes or activated ketones in the presence of an acid catalyst. Several versions of microwave-assisted Pictet-Spengler reactions have been reported in the hter-ature. Microwave irradiation allowed the use of mild Lewis acid catalysts such as Sc(OTf)3 in the reaction of tryptophan methyl esters 234 with different substituted aldehydes (aliphatic or aromatic) [150]. Under these conditions the reaction was carried out in a one-pot process without initial formation of the imine (Scheme 86). 

To the solution of the N,N-dibenzyltryptamine derivative in EtOH were added HC02NH4 (15 mol/mol tryptamine) and Pd black (2 mol Pd/mol tryptamine) and the mixture was refluxed under N2 for 12 hours. It was brought to room temperature and another batch of HC02NH4 and Pd black was added with stirring. This was followed by the addition of formic acid, and the reaction mixture was refluxed for another 12 hours.350... 

In a recently published report by MacMillan s group [121] on the enantioselective synthesis of pyrroloindoline and furanoindoline natural products such as (-)-flustramine B 2-219 [122], enantiopure amines 2-215 were used as organocatalysts to promote a domino Michael addition/cyclization sequence (Scheme 2.51). As substrates, the substituted tryptamine 2-214 and a, 3-unsaturated aldehydes were used. Reaction of 2-214 and acrolein in the presence of 2-215 probably leads to the intermediate 2-216, which cyclizes to give the pyrroloindole moiety 2-217 with subsequent hydrolysis of the enamine moiety and reconstitution of the imidazolid-inone catalyst. After reduction of the aldehyde functionality in 2-217 with NaBH4 the flustramine precursor 2-218 was isolated in very good 90 % ee and 78 % yield. 

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