Syntheses and Reactions of 2,2-Disubstituted Cyclopentane-1,3-diones. Part 8. Conversion of 2-Alkyl-2-(2-oxopropyl)cyclopentane-1,3-diones into 2,3,5- and 2,3,4-Trisubstituted Cyclopent-2-enones by Intramolecular Aldolizations to 2,3-