ortho Diquaternary Aromatic Compounds. IV. Acid-catalyzed Rearrangements of Polyalkyltetralones and Related Ketones

The ketones 1,1,4,4-tetramethyl-2-tetralone ( 1 a), 1,1,4,4,7-pentamethyl-2-tetralone ( 1 b), and 1,1,4,4,6-pentamethyl-2-tetralone ( 1 c) undergo rearrangement on heating with aluminum chloride or ferric chloride in tetrachloroethane or nitromethane into mixtures of their respective isomeric ketones, 1-acetyl-1,3,3-trimethylindane ( 2 a) and 2,2,4,4-tetramethyl-1-tetralone ( 3 a) from 1 a, 1-acetyl-1,3,3,6-tetramethylindane ( 2 b) and 2,2,4,4,7-pentamethyl-1-tetralone ( 3 b) from 1 b, and 1-acetyl-1,3,3,5-tetramethylindane ( 2 c) and 2,2,4,4,6-pentamethyl-1-tetralone ( 3 c) from 1 c. A quantitative study using g.l.c. of the distribution of the ketones with time shows that the sequence of the rearrangement is: . A methyl group homologously para to the carbonyl ( 1 c) accelerates the rearrangement. The same kind of rearrangement takes place during Friedel-Crafts cyclialkylation with 2,2,5,5-tetramethyltetrahydrofuranone. A unifying reaction mechanism is postulated to account for the rearrangements. This mechanism also accounts for the rearrangement and fragmentation products from treatment of 1,1,4,4-tetramethyl-2,3-dioxotetralin ( 9 ) with aluminum chloride or sulphuric-acetic acids. The products from 9 include 1-acetyl-1,3,3-trimethyl-2-indanone, 1,1,3-trimethyl-2-indanone, and, from the aluminum chloride - catalyzed rearrangement, 5(or 6)-acetyl-1,1,3-trimethyl-2-indanone.