PORPHYRINS WITH EXOCYCLIC RINGS .1. CHEMISTRY OF 4,5,6,7-TETRAHYDRO-1H-INDOLES - SYNTHESIS OF ACETOXY DERIVATIVES, DIHYDROINDOLES, AND NOVEL PORPHYRINS WITH 4 EXOCYCLIC RINGS

A variety of 4,5,6,7-tetrahydro-1H-indoles (THI's) and 4-oxo-4,5,6,7-tetrahydro-1H-indoles (4-oxoTHIs) have been synthesized from cyclohexanone and 1,3-cyclohexanedione, respectively. The THI's reacted regioselectively with lead tetraacetate in acetic acid to give the 7-acetoxy derivatives. The isomeric 4-acetoxyTHI's were prepared by first reducing the corresponding 4-oxoTHI's with sodium borohydride and then reacting the resulting hydroxyTHI' s with acetic acid-pyridine. Both series of acetoxyTHI's underwent elimination of acetic acid when heated with pyridine-acetic anhydride to give dihydroindoles. The 7-acetoxyTHI's were hydrolyzed with potassium hydroxide in methanol-water and carefully neutralized with hydrochloric acid to give the corresponding hydroxyTHI carboxylic acids. Treatment with potassium ferricyanide in refluxing acetic acid gave good yields of tetrapropanoporphyrins when 3-methyl-, 3-ethyl-, or 3-n-propyl substituents were present. The 3-phenylTHI gave variable yields of the corresponding tetraphenylporphyrin. The 3-isopropylTHI gave only trace amounts of porphyrin under these conditions, and the 3-tert-butylTHI failed to give any porphyrin product. THI's with 6-methyl or 6,6-dimethyl substituents were prepared in two steps from 5-methyl-1,3-cyclohexanedione or dimedone, respectively. These compounds also reacted smoothly with lead tetraacetate to give the 7-acetoxy derivatives in high yield. Attempts to convert the 6,6-dimethylTHI's into symmetrical porphyrins were unsuccessful, although the 6-methylTHI gave a mixture of porphyrin stereoisomers in low yield. The influence of alkyl substituents and carbocyclic rings on the cyclotetramerization of THI's is discussed.