Conversion of 2-alkylcinnamaldehydes to 2-alkylindanones via a catalytic intramolecular Friedel-Crafts reaction.
The preparation of indanones by the intramolecular acylation of 3-arylpropanoic acids or halides requires the use of noncatalytic acid promoters. In the presence of 5-10 mol % FeCl(3), in situ generated dimethyl acetals of (E)-2-alkylcinnamaldehydes cyclize to 1-methoxy-2-alkyl-1H-indenes in good-to-high yields. The 1-methoxyindenes were converted in high yield into 2-alkylindanones by treatment with triethylamine, to effect isomerization to the isomeric enol ethers, followed by acid-catalyzed hydrolysis. Thus, a catalytic, intramolecular Friedel-Crafts reaction leading to 2-alkylindanones from 2-alkylcinnamaldehydes was developed.
Womack
Gary B
GB
Firmenich, Corporate R&D Division, P.O. Box 5880, Princeton, New Jersey 08543, USA. gary.womack@firmenich.com
Angeles
John G
JG
Fanelli
Vincent E
VE
Heyer
Christie A
CA