Synthesis of Pyrrolizin-3-One

The latter cyclize mnch easier than 2-vinylpyrroles containing only nitrile or amide functions, this often occnrring already at a stage of their synthesis [563,564]. 

SCHEME 2.88 Synthesis of functionalized 3-vinylpyrroles from pyrrole-3-cardodithioates with methylene active nitriles. 

SCHEME 2.89 Synthesis of pyrrolothiazolidines from pyrrole-2-carbodithioate and halo-acetylenes via the intermediate pyrrole-2-vinylthiolates. 

The yields of pyrrolizin-3-ones range from 61% to 75% (Table 2.11). The decrease in yields is due to instability of the esters in KOH/DMSO system as well as configurational hindrances. 

This reaction is chemoselective. In cases when other functions (such as nitrile or acetyl) capable of interacting with the NH-pyrrole moiety are adjacent to the double bond, only ethoxycarbonyl group takes part in the cycUzation. 

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SCHEME 2.90 Synthesis of pyrrolizin-3-ones from pyrrole-2-carbodithioates and methylene active esters. 

SCHEME 2.91 Synthesis of pyrrolizin-3-one by the acid-catalyzed hydrolysis of 3-iminopyrrolizine. 

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