Nucleophilic Addition of 1-Acetylindole Enolates to Pyridinium Salts. Stereoselective Formal Synthesis of (±)-Geissoschizine and (±)-Akagerine via 1,4-Dihydropyridines
作者:M.-Lluïsa Bennasar、Juan-Miguel Jiménez、Bernat Vidal、Bilal A. Sufi、Joan Bosch
DOI:10.1021/jo9911894
日期:1999.12.1
Addition of the enolate derived from 1-acetylindole (3) to pyridinium salt 4b followed by acid-induced cyclization of the resulting 1,4-dihydropyridine 5b in the presence of lithium iodide gives tetracyclic 3,7-methano[1,4]diazonino[1,2-alpha]indole 6b, which has subsequently been elaborated into the (E)-ethylidene derivative 7b. From this compound is reported a stereocontrolled route to (+/-)-geissoschizine, involving closure of C ring by Pummerer reaction, methanolysis of the resulting pentacyclic lactam 12, and desulfurization. A similar synthetic sequence starting from the enolate of 3 and 2-fluoropyridinium salt 15b gives access to the pentacyclic dilactam 2, which had previously been converted to (+/-)-akagerine through opening of the piperidone (D) ring.
作者:M.-Lluïsa Bennasar、Bernat Vidal、Bilal A. Sufi、Joan Bosch
DOI:10.1039/a807868h
日期:——
A stereoselective synthesis of pentacyclic dilactam 1, a known precursor of the indole alkaloid akagerine, involving addition of the enolate of 1-acetylindole 2 to 3-acetyl-2-fluoropyridinium salt 3, cyclization of the resultant 1,4-dihydropyridine, elaboration of the (E)-ethylidene substituent and closure of the C ring by Pummerer reaction, is reported.