The following 14-membered ring diynes have been synthesized: cyclotetradeca-4,ll-diynone (4), cyclotetradeca-4,lldiyne-1,8-dione (6)-the corresponding exomethylene derivatives 5 and 7 , as well as 1,8-dioxacyclotetradeca-4,1l-diyne (8). The synthesis of the diketal of 4 was achieved 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 of 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 obtained by treating the ketals 10 and 14, respectively, with HC1. The ketones 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 investigations of single crystals of 6 and 8 revealed chair conformations with a zig-zag arrangement, employing two anti orientations of the two chains between the triple bonds. Azig-zag arrangement of the chain containing the carbonyl group was also found in 4. In 3b and 7 a Ci symmetry was found, with only one anti conformation in each chain. Molecule 6 crystallizes with C2h symmetry and 8 with a center of symmetry.Medium-sized cyclic diynes are useful models to probe the interactions between two triple bonds in close proximity. By means of photoelectron spectroscopy it was found that the interaction between the triple bonds depends considerably on the ring size"]. Structural investigations on cyclodeca-l,6-diyne (1) [2] and cyclohexadeca-1,lO-diyne (2)L3], showed that the uneven chains between the triple bonds tend to arrange in a zig-zag arrangement, such as to adopt a chair conformation. In the case of cyclotetradeca-1,8-diyne it was shown that the conformer 3b with two gauche interactions (instead of the zig-zag arrangement 3a) is favored in the solid ~t a t e [~.~J .In order to understand conformational effects of medium-sized rings better we synthesized cyclotetradeca-4,ll-diynone (4), 5-methylenecyclotetradeca-l&diyne (5), cyclotetradeca-4,11 -diyne-l$-dione (6), 5,12-dimethylenecyclotetradeca-l,8-diyne (7) and 1,8-dioxacyclotetradeca-4,ll -diyne (8). Synthesis of 4-8Our synthesis of 4 commenced with 1,5-dibromopentanand its transformation to the ethylene ketal 9. This compound then reacted with the dilithium salt of 1,8-nonadiyner7] to yield the ketal 10, which can be converted to 4 by treatment with 1.5 N HCl. A second path to 10 is the reaction of the dilithium salt of 11, l l a , with 1,5-diiodopentane. Both alternatives gave 10, but in low yields (7%). The synthesis of the diketone 6 also starts with 9. The reaction of 9 with two equiv. of lithium acetylide ethylenediamine adductrs] yields a mixture of 11 (300/), 12 (22%) and 13[8,9] (3%), which can be separated by fractional distillation. The reaction of the lithium salt l l a with 9 gives the diketal 14 which gives, after hydrolysis, the diketone 6 in 7% yield (Scheme 1).The ketones 4 and 6 were transformed to 5 and 7, respectively, by...

The syntheses of [11]metacyclophane-2,9-diyne (3), [4.4]metacyclophane-2,12-diyne (4), [4.4]orthometacyclophane-2,12-diyne (5), (Z)-[10]metacyclophane-5-ene-2,8-diyne (6), [10]metacyclophane-2,8-diyne (7), and 5-isopropylidene[9]metacyclophane-2,7-diyne (8) have been achieved. The systems could be stabilized by protecting the triple bonds in 3−8 with the Co2(CO)6 moiety. PE spectroscopic investigations of 3 and 6−8 gave no clear-cut evidence for homoconjugative interactions among the π fragments. The triple bonds in 3−8 could be transformed into the corresponding cis double bonds by applying 2−5 molar equiv of Schwartz's reagent (28). Treatment of 3, 4, and 7 with t-BuOK allows the transformation of the propargylic moieties into allenic moieties, whereas the same treatment of 5 and 6 transforms the 2-butynyl bridges into 1,3-butadiene bridges, giving rise to several isomers. The structural assignments of 3−8 and their reaction products are based on their spectroscopic properties.

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The following monocyclic and bicyclic 14‐membered diynes were treated with [CpCo(cod)]: 1‐oxacyclotetradeca‐4,11‐diyne (2), 1,8‐dioxacyclotetradeca‐4,11‐diyne (3), cyclotetradeca‐4,11‐diynone (4), cyclotetradeca‐4,11‐diyne‐1,8‐dione (5), 1,1,8,8‐tetramethyl‐1,8‐disilacyclotetradeca‐4,11‐diyne (6), 1‐allyl‐1‐azacyclotetradeca‐4,11diyne (7), 1,8‐dipropyl‐1,8‐diazacyclotetradeca‐1,11‐diyne (8), 1,8‐diallyl‐1,8‐diazacyclotetradeca‐4,11‐diyne (9), 1,8‐diazabicyclo[6.6.4]octadeca‐4,11‐diyne (10), 1,8‐diazabicyclo[6.6.6]eicosa‐4,11‐diyne (11), 1,10‐diazabicyclo[8.6.6]docosa‐13,19‐diyne (12) and 1,12‐diazabicyclo[10.6.6]tetracosa‐15,21‐diyne (13). In all cases we obtained an intramolecular cyclobutadiene complex stabilized with a CpCo fragment (15–26). For 3 we could isolate, besides the cyclobutadiene complex 16, the trimerization product 28. In the cases of 15, 16, 18, 20, 23, 25, and 26 the structure of the cylobutadiene complexes could be confirmed by X‐ray studies. Common to all structures is a boat‐like conformation of the tricyclic unit containing the cyclobutadiene ring. The two cycloheptene units adopt a chair conformation in which the heteroatom is removed from the metal center.

Syntheses and Properties of Medium-Sized Metacyclophanediynes. -The readily synthesized cyclic diynes (III) are hydrogenated under treatment of Schwartz's reagent to the corresponding (Z,Z)-cyclophanedienes (IV). In the presence of tBuOK the compounds (IIIa) and (IIId) form allenic moieties, e.g. (V), whereas cyclophanes (IIIb) and (IIIc) show a different isomerization behavior. In the latter case butadiene moieties are formed from the triple bonds, e.g. (VI) and (VII). -(RAMMING, M.; GLEITER, R.; J.