The direct formation of 2,2-disubstituted 1,3-cyclopentanedione compounds by a Lewis acid catalysed reaction with 1,2-bis(trimethylsilyloxy)cyclobutene proceeds in good to excellent yields with unhindered ketals, but steric hindrance reduces the yields considerably. A carbonyl group α or β to the ketal, or a carbon–carbon double bond α to the ketal, stops the reaction completely. Orthoesters do not give geminally acylated products in synthetically useful yields.
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Wu et al. (1993) studied this question.
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