SYNTHESIS AND PROPERTIES OF ,9-TETRAMETHYL-1-OXA-CYCLOUNDECANE-5,6,7,8-TETRONE AND 0-TETRAMETHYL-1-OXA-CYCLOTRIDECANE-6,7,8,9-TETRONE

The synthesis of ,9-tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone (9 ) and 0-tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetrone (10) has been achieved in a multistep procedure. The key steps in this synthesis we re the ring closure of 23 and 24 to 25 and 26, respectively, and the o xidation of the triple bond with RuO2/NaIO4 to the dihydroxydiketones 31 and 32. Compound 9 is the first cyclic tetraketone for which an int ramolecular donor-acceptor stabilization has been found. A strong tran sannular interaction between the ether oxygen and the C4O4 unit in 9 w as detected by X-ray studies on single crystals of 9. The transannular distance is 2.7-2.8 Angstrom. Further evidence for a strong transannu lar interaction was obtained from the comparison of the reduction pote ntial and the first band in the UV/Vis spectrum with the corresponding values from other open-chain tetraketones. These findings were substa ntiated by PE investigations on 9. The crystal structures of the dihyd roxydiketones 31 a and 32 a showed that, in the case of the eleven-mem bered ring (31 a), there are also short transannular distances between the ether oxygen and the C2O2 moiety (2.5 Angstrom, and 2.9 Angstrom) . In the case of the thirteen-membered ring (32 a), no transannular in teractions were found in the solid state.