Triynes, rearrangement

A variety of palladium-catalyzed dimerizations of conjugated enynes and their additions to diynes and triynes gave rise to styrene and phenylacetylene derivatives, respectively. Inter alia, 1,2,4-cyclohexatrienes have been invoked as intermediates in these reactions [134], 5,6-Diphenyl-l,2,4-cyclohexatriene has been proposed as an intermediate in the rearrangement of 4,4-diphenylcyclohexa-2,5-dienylidene to o-ter-phenyl and its possible existence was supported by quantum-chemical calculations [135],... 

Intramolecular 2 + 2 + 2-cycloisomerizations of cyclic triynes and enediynes have been reported with RhCl(CO)(PPh3)2.126 The transition metal-catalysed rearrangement of alk-5-ynals to /-alkynyl ketones and cyclopent-l-enyl ketones was developed using [Rh(P(OPh)3)2]BF4 or Cu(OTf)2 as a catalyst and the effect of substituents on the partition to products was elaborated (Scheme 84).127... 

Oxidative coupling of /ra/w,rra/ij-4,10-tetradecadien-l,7,13-triyne (257) and subsequent prototropic rearrangement of the coupling products yielded mainly the geometrical isomers of monodehydro[14]annulene (258 and 259) and a byproduct, l,8-bisdehydro[14]annulene (260) . Formation of 260 indicates that dehydrogenation occurs under the basic conditions of prototropic rearrangement. 

Prototropic rearrangement. Cyclooctadeca-l,3,7,9,13,15-hexayne heated 25 min. at 90° with K-ferf-butoxide in ferf-butanol cyclooctadeca-l,7,13-(czs)-triene-3,9,15-(fran5)-triene-5,l 1,17-triyne. Y ca. 50%.—The product is planar, contains 18 TT-electrons in conjugation, and is the first monocyclic system known with more than the classical sextet. F. Sondheimer and R. Wolovsky, Am. Soc. 81, 1771 (1959). 

A one-pot synthesis and derivatization of diynes and triynes is reported. The polyyne framework was formed from a dibromoolefm precursor 96 based on a carbenoid rearrangement, and the resulting Li-acetylide is then transmetallated with zinc chloride which then allowed for the divergent preparation of aryl polyynes 97 via Negishi palladium-catalyzed cross-coupling reactions. 

Rather good yields (72-91%) of 221 were obtained, and their relevance to the mechanism of the CpCo-catalyzed cyclization of the triyne to the angular [3]-phenylene was established by allowing 221 to rearrange thermally to 222 (see Scheme 36). 

Typical substrates for Fritsch-Buttenberg-Wiechell rearrangements are chloro-ethenes and ge/w-dibromoethenes. They are readily prepared by Wittig reaction from the corresponding ketones. The method offers a versatile entry to aromatic or heterocyclic acetylenes. Moreover, ethynyl groups can embark also on 1,2-migrations, thus, making simple or functionalized diynes and triynes (e.g., 321) accessible (Scheme 1-250). ... 

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