Synthesis of Esters of 3‐(2‐Aminoethyl)‐1H‐indole‐2‐acetic Acid and 3‐(2‐aminoethyl)‐1H‐indole‐2‐malonic acid (= 2‐[3‐(2‐aminoethyl)‐1H‐indol‐2‐yl]propanedioic acid) 4th communication on indoles, indolenines, and indolines

Alkyl 3‐(2‐aminoethyl)‐1H‐indole‐2‐acetates 6a and 6b are synthesized starting from methyl 1H‐indole‐2‐acetate (2) via methyl 3‐(2‐nitroethenyl)‐1H‐indole‐2‐acetate (4) and the alkyl 3‐(2‐nitroethyl)‐1H‐indole‐2‐acetates 5a and (Scheme 1). Analogously, diisopropyl 3‐(2‐aminoethyl)‐1H‐indole‐2‐malonate 20b is obtained from diisopropyl 1H‐indole‐2‐malonate 11c (Scheme 4). An alternative synthesis of 20a and 20b follows a route via 15–18 and the dialkyl 3‐(2‐azidoethyl)‐1H‐indole‐2‐malonates 19a and 19b, respectively (Scheme 3). The aminoethyl compounds 6a and 20a are easily transformed into lactams 7 and 21, respectively. Procedures for the preparation of the indoles 2 and 11a and of the alkylating agent 14 are described. A tautomer 12 of 11a is isolated.