Systems with One Heteroatom at a Ring Junction

in the form of N-(2-pyridylcarbonyl)proline Pro undergoes 1,3-dipolar cycloaddition with 2-chloroacrylonitrile to give two tetracyclic products and 61b in 5% yield (85TL5447). When Pro-OMe was heated with methyl cinnamate and benzaldehyde in toluene for several hours, two iso- 

An angiotensin-converting enzyme inhibitor 64 was prepared in several steps from L-pyroglutamic acid. The formation of the bicyclic system was achieved with methylene glutaric anhydride (89TL3621). 

A-Phenylthiomethylpipecolic acid methyl ester afforded with methyl cin-namate and a mixture of two regioisomers 65 and 66 (84TL1579). Pipecolic acid and diethyl fumarate or maleinate gave three isomers (85TL2775). 

After reduction and reaction with 2,5-dimethoxytetrahydrofuran, l-Asparagine was converted into a pyrrole derivative which was cyclized with trifluorosulfonyl anhydride into 67 [90H(31)9], 

The alkaloid tylophorine was synthesized from ornithine. Ornithine was first converted into 1-pyrroline which gave the alkaloid septicine 68 after several transformation steps. This alkaloid was then oxidized into tylophorine [82JCS(P1)2477]. 

---