Pictet-Spengler synthesi

Acetaldehyde is typically formed after ingestion of alcohol (see Section 3.4.7). Since the urine product is racemic, it would appear that a chemical Pictet-Spengler synthesis is being observed here rather than an enzymic one. 

The mechanistically similar Pictet-Spengler synthesis is also much used for the preparation of 1,2,3,4-tetrahydroisoquinolines, starting from a... 

Pictet-Spengler synthesis is another method of preparing isoquinolines. (3-phenylethylamine reacts with an aldehyde to produce an imine, which undergoes acid-catalysed cyclization, resulting in the synthesis of the tetrahydroisoquinoline system. Again, tetrahydroisoquinoline can he aromatized hy palladium dehydrogenation to produce an isoquinoline system. 

Pictet-Spengler Synthesis. An acidic catalyst results in the condensation of / 1-pheiicthylamines with carbonyl compounds to give 1,2.3,4-tetiahydroisoquinolines. 

Whereas 5-endo-trig processes are unfavorable, 6-endo-trig cyclizations are allowed. For this reason the reaction conditions used for several well-known preparations of six-membered rings cannot be used to prepare the corresponding five-membered rings. For example, treatment of phenethylamines with aldehydes and acid yields tetrahydroisochinolines (Pictet-Spengler synthesis), but treatment of benzylamines under these conditions does not yield dihydroisoindoles (Scheme 9.6). 

The Pictet-Spengler synthesis is usually used when the tetrahydroisoquinoline oxidation level is required. 

Closely related to the Bischler-Napieralski synthesis is the Pictet-Spengler synthesis, which utilises aldehydes rather than acylating species. Condensation of (3-arylethylamines with aldehydes produces imines such as... 

Whaley, W.M. and Govindachari, T.R. (1951). Organic reactions, 6, p.151 (Pictet-Spengler synthesis). 

N-Hydroxymethylation occurs upon the catalytic decomposition of dimethoxymethane generating formaldehyde followed by Picket-Spengler cyclization forming the tetrahy-droisoquinoline. A review of the Pictet-Spengler synthesis in the preparation of tetrahydroiso-quinolines is provided (1). 

The mammalian alkaloids are formed from aromatic amino acids and their metabolically derived amines by reaction with carbonyl substrates at physiological pH. The reaction is catalyzed by acid and is commonly referred to as the Pictet-Spengler cyclization (I0a,b,II). Winterstein and Trier in 1910 proposed that the Pictet-Spengler reaction might be of significance in the biosynthesis of benzylisoquinoline alkaloids in plants (5a). The carbonyl compounds participating in the Pictet-Spengler synthesis of mammalian alkaloids are aldehydes and a-keto acids, which are produced... 

Whaley, W. M., Govindachari, T. R. The Pictet-Spengler synthesis of tetrahydroisoquinolines and related compounds. Org. React. 1951, 6, 151-190. 

Connors, R. V., Zhang, A. J., Shuttleworth, S. J. Pictet-Spengler synthesis of tetrahydro- -carbolines using vinylsulfonylmethyl resin. Tetrahedron Lett. 2002, 43, 6661-6663. 

Perlolyrine (14) is an alkaloid from the perennial rye grass Lolium perenne, and is of a different type from the alkaloids obtained previously from Lolium species. The alkaloid has been synthesised by a standard Pictet-Spengler synthesis using 5-acetoxymethyl-2-formylfuran and tryptophan, followed by oxidative dehydrogenation-decarboxylation. 

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