2658 NOTES [Vol. 59, No. 8 tion band of the carbonyl group at 1680 cm-1, corre- sponding to the vinyl ketone. An acid-catalyzed cycliza- tion (phosphoric acid-formic acid (1:1), reflux)5' of the divinyl ketone (5) gave 2-alkyl-2-cyclopentenone (6) (6a: 34%; 6b: 22%) and its exo-enone isomer (7) (7a: 20%; 7b: 10%). In our reaction system, a chemical yield of 2-cyclopentenones can be 32 to 54% because the isomerization of 7 to 6 could be accomplished by heating ...
