G. Mloston et al., Unexpected products from the reaction of 2,2,4,4-tetramethylcyclobutane-1,3-dione with the Makosza reagent, HELV CHIM A, 82(8), 1999, pp. 1302-1310
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.