Silica gel-mediated self-aldol reactions of highly volatile aldehydes under organic solvent-free conditions without reflux condenser

Silica gel-mediated self-aldol reactions were catalyzed by piperidine to give the corresponding α,β-conjugated aldehydes in good yields. The aldol reactions of 4-nitro-, 4-trifluoromethyl-, and 4-chlorobenzaldehydes with acetone afforded the corresponding aldol products. Highly volatile aldehydes and acetone could be employed even without a reflux condenser for these reactions. Silica gel could be recycled five times without any significant decrease of the yields of the products.