Amino cyclization

Imidazole-4-carboxylic acid, 5-amino-cyclization, 5, 583 decarboxylation, 5, 434—435 ethyl ester diazotization, 5, 414 synthesis, 5, 477... 

Intramolecular reductive amino cyclization.1 The key step in a synthesis of the ergot alkaloid aurantioclavine (3) from 3-formylindole (1) involves treatment of the nitro olefin 2 with amalgamated zinc in refluxing methanolic 2 N hydrochloric acid. Zn-HOAc, Fe-HOAc, SnCl2-HCl are not useful for this purpose. Cyclization is believed to involve an intermediate hydroxylamine, which can be isolated from short-term reactions. 

Scheme 8 Catalytic enantioselective t rt-amino cyclization by asymmetric binary acid catalysis...

Application of the amino-cyclization method (52) to the compound 77 was also developed by Somei et d. Reduction of the nitroester 77 with amalgamated zinc in hydrochloric acid yielded the seven-membered ring system as a mixture... 

Somei s group (24) has rfxtned a similar one-pot cyclization of the nitro-olefin 147 by reductive amino-cyclization for the synthesis of di-aurantioclavine (148). They later fiplied this method to the synthesis of d/-clavicipitic acids (84,85) (47). Nitroolefin 77, prepared from 3-formylindole (37), was treated with amalgamated zinc in HCl and methanol to give Ae clavicipitic acid methyl esters (7 8, 7 9) (Scheme 27). 

---