Nebenprodukte bei der Fulven-Synthese nach Thiele

Abstract

Although it is well known that the base-catalysed condensation of cyclopentadiene with carbonyl compounds (according to Thiele) gives good yields with ketones and extremely low yields with aliphatic aldehydes, the reasons for this failure have been unknown so far. In the present contribution the complex product mixture resulting from Thiele-condensation of cyclopentadiene with acetaldehyde has been analysed and fulvenes 4, 7, 9 and 10 as well as cyclopentadienes 6 and 8 have been isolated. A reasonable reaction sequence (Schema 1) is presented. By-products are formed mainly by 2 processes: (1) Formation of disubstituted cyclopentadienide 3; and (2) reaction of the fulvenes 4 and 5 (postulated as an intermediary) with the nucleophiles present in solution.