Pictet-Spengler ring closur

Peroxidase and laccase enzymes were used to catalyze the decarboxylation of various tetrahydroisoquinoline-1-carboxylic acids to give high yields of the corresponding 3,4-dihydroisoquinolines (204). Compounds such as 125 (Scheme 29) are derived from Pictet-Spengler ring closure via a-keto acid and aryl amine condensation and are of biogenetic importance. The possible relevance of iso-... 

An asymmetric carbon-transfer reaction was also performed by using 2-(/>-tolyl)sulfmylmethyltetrahydro-l,3-oxa-zine 143 as the chiral aldehyde equivalent in the Pictet-Spengler ring closure with tryptamine, but only moderate diastereoselectivity ( 40% de) was observed in favor of the (l/ )-tetrahydro-/3-carboline 165, and the enantiopure main product could be isolated only in low yield (Scbeme 26) <2001H(55)1937, 2004T9171>. 

A 1-benzyl analogue of the preceeding structure was obtained by way of an asymmetric Pictet-Spengler ring closure of the chiral carbamate shown (a derivative of (-)-8-phenylmenthol) with an enol methyl ether of... 

Indolo[3,2-Z)]quinolizidine (240) was obtained from the Pictet-Spengler ring closure of (239) (Equation (58)) <57JA5686, 72CPB1745>. The indolo[2,3-i]quinolizidine ring can be prepared analogously <62BRP891157>. 

Highly activated hydroxylated aromatic rings permit Pictet-Spengler ring closure under very mild, physiological conditions. ... 

Pictet-Spengler ring closure Reactions under physiological conditions... 

Pictet-Spengler ring closure with ketones l,2,3,4-Tetrahydro-9H-pyrido[3,4-b]indoles from tryptamines... 

Scheme 13.61. A path, involving a Pictet-Spengler ring closure of the imiue formed from the reaction of tyramine with secologanin to strictosidine and thence to dehydrogeissoschizine. The process is supported by a large number of feeding experiments with labelled compounds. (Much of this chemistry has been reviewed and, at any rate, is too extensive to repeat here. See, for example, Scott, A. I. in Hey, D. H. Wiesner, K. F. (eds.), MTP International Review ofScience Vol. 9, Butterworths, London, 1973,pp. 105 ft) The final cyclization and ring closure processes appear to be spontaneous.

Hydrogen chloride Benzoxazepinoisoquinoline ring Unusual Pictet-Spengler ring closure... 

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