Part of the projected Doctoral Thesis by M. P., Universität Giessen.—M. P. wishes to thank the DAAD for a stipend. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
The first unsaturated carbonyl derivative to react at C-5 with electrophiles is the dianion (1). It forms adducts (2) or (3) which can be cyclized to tetrahydrofurans or- pyrans if they contain OH groups.