PREPARATION AND STRUCTURES OF CYCLOTETRADECA-4,11-DIYNONE, CYCLOTETRADECA-4,11-DIYNE-1,8-DIONE - THEIR EXOMETHYLENE DERIVATIVES, AND 1,8-DIOXACYCLOTETRADECA-4,11-DIYNE

The following 18-membered ring diynes have been synthesized: cyclotetr adeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (6), the c orresponding exomethylene derivatives 5 and 7, as well as 1,8-dioxacyc lotetradeca-4,11-diyne (8). The synthesis of the diketal of 4 was achi eved by the reaction of the ethylene ketal of 1,5-dibromopentan-3-one (9) with the dilithium salt of 1,8-nonadiyne. Similarly, the diketal o f 6 was prepared from the dilithium salt of the ethylene ketal of 1,8- nonadiyn-5-one 11 with 9. The unprotected ketones 4 and 6 were obtaine d by treating the ketals 10 and 14, respectively, with HCL. The ketone s 4 and 6 were transformed to the exomethylene derivatives by a Wittig reaction. The reaction of the dilithium salt of 5-oxanona-1,8-diyne ( 16a) with 1,5-dibromo-3-oxapentane (15) yielded 8. X-ray investigation s of single crystals of 6 and 8 revealed chair conformations with a zi g-zag arrangement, employing two anti orientations of the two chains b etween the triple bonds. A zig-zag arrangement of the chain containing the carbonyl group was also found in 4. In 3b and 7 a C-i symmetry wa s found, with only one anti conformation in each chain. Molecule 6 cry stallizes with C-i, symmetry and 8 with a center of symmetry.