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Part-A Studies on 2-methyl indoline derivatives…..
hydrogenation of 2, 3-dialkylindoles often afford relatively much lower yields. It
is essential, however, that the indole being hydrogenated must either be acid
stable or be very rapidly reduced relative to being polymerized. 57
When the above-mentioned hydrogenation of 1, 2, 3, 4-tetrahydro-9methylcarbazole
is continued, a second product is formed 79 which is probably
dodecahydro-9-methylcarbazole. 79 Under the appropriate conditions indole,
2- and 3-methylindole, and 1, 2-dimethylindole can be catalytically
hydrogenated to the corresponding octahydroindoles. 76 The A-B ring junction
58-61, 80-84
in such compounds is cis-fused as shown in Fig. A.3.
Fig. A.3
Several examples are known 49, 58, 85, 86 in which catalytic hydrogenation
of an indole ring affords the 4, 5, 6, 7-tetrahydroindole derivatives. In one of
these cases 85 an aliphatic nitro group in the molecule remains unreduced
under conditions which would normally effect its conversion to an amino
group.
5. REDUCTIVE CLEAVAGE OF SUBSTITUENTS FROM THE INDOLE
NUCLEUS
2-ethoxyindole affords 66% of indole and 9.8% of indoline upon
reduction with borane in tetrahydrofuran. 73 Similar cleavage of a 2-substituent
occurs when compound (1) is exhaustively hydrogenated in the presence of a
platinum catalyst to afford skatole and piperidine hydrobromide. 87 If this
hydrogenation is arrested after the uptake of three moles of hydrogen or if it is
affected in the presence of palladium-carbon instead of platinum, it affords
compound (2). 87 (Fig. A.4)
Department of Chemistry, Saurashtra University, Rajkot – 360 005 16