Spiro-indolenine derivatives

Other spiro pyrrolidine derivatives can be prepared from 2-oxoindolin-3-ylidine derivatives. Even the nitro derivative which is known to be extremely sensitive to base and heat, has been obtained in good yield.421,422 The spiro-indolenine framework is frequently encountered in alkaloids such as horsfilline.423... 

The formation of (49) (Table 6) may be considered as new evidence for the presence of a spiro-indolenine intermediate in the Pictet-Spengler reaction of N -hydroxytryptamine <88CC463>. Thus A-substituted N -hydroxytryptamines with cysteinals afforded only (49 R = Me, CHjOMe). In similar reactions with N -hydroxytryptamines, (49 R = H) was formed along with ) -carboline derivatives. 

The imine (101) derived from a 2-aryltryptamine and ethyl glyoxylate undergoes a diastereo-selective spirocyclization to the indolenine (102) (Equation (27)). Replacement of the ethyl ester by chiral esters, such as the 8-phenylmenth-3-yl ester, leads to asymmetric induction at the spiro carbon atom <90HCA439>. Imines derived from tryptophan esters have also been studied as substrates for the Pictet-Spengler cyclization (e.g., <87tlii31 . Enantioselective cyclizations have made use of enantiomerically pure aldehydes and tryptophan esters <92H(34)517, 93JCS(pi)43i, 93T8589>. 

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