Cyclization Studies with N-Mannich Bases of 2-Substituted Indoles

Article abstract of DOI:10.1002/hlca.19890720112

The synthesis of the indoles 7, 15, 16 with a 3-methoxyphenyl group, attached via an α-side chain of 1, 2, or 3 CH2 units, is reported.These compounds, after appropriate protection at C(3), were transformed into the N-<(dimethylamino)methyl>indoles 22, 23, and 24, respectively.When treated with AcCl, these N-Mannich bases gave, in two cases, stable N-(chloromethyl)indoles 25 and 26.In the presence of SnCl4, ring closure occured via electrophilic attack of 1-methylideneindolium ions on the methoxyphenyl group.Formation of seven-membered rings (<*> 27, 28) and eight-membered rings (<*> 29) was found to be a favorable process.Cyclization to six-membered rings did not occur within this series.