Unexpected products from the reaction of 2,2,4,4-tetramethylcyclobutane-1,3-dione with the Makosza reagent

Reaction of 2,2,4,4-tetramethylcyclobutane-1,3-dione (2) under phase-transf er-catalysis (PTC) conditions (CHCl3/aqueous NaOH) yielded a complex mixtur e of unexpected products (Scheme,2). From the organic phase, three ring-enl arged products 7-9 with a cyclopentane-1,3-dione (cf. 7 and 9) or a cyclope ntenone skeleton (cf: 8) were isolated in low yield. After acidification of the aqueous phase, the oily residue was treated with CH2N2, and methyl 3-o xopentanoate 12 and dimethyl 2-hydroxybutanedioate 13 were obtained in almo st equal amounts. The structures of 8 and 9 were established by X-ray cryst al-structure analysis (Fig.). Mechanisms for the formation of the products, initiated by nucleophilic attack of trichloromethanide ion and opening of the cyclobutane ring, are proposed in Schemes 3 and 4.