Reactions of 1,2-bis(trimethylsilyloxy)cycloalkenes with the diethyl acetals of aldehydes.

[reaction: see text] Lewis acid-mediated reactions of 1,2-bis(trimethylsilyloxy)cyclobutene with acetals derived from a variety of aldehydes, followed by treatment with Amberlyst 15 resin in TFA, yielded 1,3-cyclopentanedione products, but reactions with 3,3-dimethyl-1,2-bis(trimethylsilyloxy)cyclobutene led to 1,2-cyclopentanediones. Reactions of 1,2-bis(trimethylsilyloxy)cyclopentene gave intermediates that did not undergo skeletal rearrangement with Amberlyst 15 resin in TFA.