66. “Cyclization Studies with N-Mannich bases of 2-substituted indoles”
    Burger, U.; Bringhen, A. O.
    Helv. Chim. Acta 1989, 72, 93-100.

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 occurred 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.

DOI : 10.1002/hlca.19890720112 

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