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Synthesis of Annulated Indolines by Reductive Fischer Indolization
Author(s) -
Dierks Anna,
Schmidtmann Marc,
Christoffers Jens
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201806302
Subject(s) - iminium , diastereomer , chemistry , medicinal chemistry , crystal structure , organic chemistry , catalysis , stereochemistry
Cyclic β‐oxoesters and arylhydrazine derivatives were converted at ambient temperature under modified Fischer indolization conditions to furnish annulated indolines with quaternary bridgehead carbon center. Reaction conditions were Brønsted acidic (with CF 3 CO 2 H), but also reductive (with Et 3 SiH). The latter reduced intermediate iminium ions under formation of the 2,3‐dihydroindole product constitutions. Racemic products (13 examples) were obtained as single diastereoisomers with relative cis ‐configuration, which was proved in two cases by single‐crystal X‐ray structure analysis. Conversion of 4‐bromo‐1‐indanone‐2‐carboxylate and 4‐bromophenylhydrazine gave indeno[1,2‐ b ]indolines with either 1‐bromo, 8‐bromo, or 1,8‐dibromo substitution, which were further diversified by Suzuki coupling reactions with several arylboronic acids (nine examples).