Butatriene, 1,4-diphenyl

Cumulenes such as butatrienes and hexapentaenes can undergo cycloaddition at several possible double-bond sites. The electrophilic l,l-diphenyl-4,4-bis(trifluoromethy )butatriene (34), however, reacts with ketene acetals and geminal enediamines at the central double bond exclusively.25 In the case of the ketene acetal cycloadduct 35 (R1 = H R2 = R3 = OMe). acid-catalyzed hydrolysis gives the cyclobutanone. 

However, difficulties arise if the acetylenic compounds contain also halogen277 or if the products are olefins that are attacked by sodium and liquid ammonia. For instance, only ethylbenzene and the acetylide are formed from phenylacetylene.278 Also, the conjugated dienes formed from the corresponding diynes or enynes are further reduced (see page 8) in such cases reduction by a zinc-copper couple in powder form279 has proved valuable, but diphenyl-butatriene is then formed by 1,4-addition to diphenyldiacetylene.280... 

Buta-l,2,3-trienes. Newkome et al. were able to prepare the unstable (Z)-and (E)-l,4-diphenyl-l,4-di(2-pyridyl)butatrienes, (2) and (3), by didehydrox-ylation of (1) with P214 in anhydrous pyridine. Reduction of (1) with the more usual reagents (SnCl2 or PBra) resulted mainly in formation of (4). 

Bromo-3,3-(diphenylallyl)triphenylphosphonium bromide added to a cold soln. of triethylamine in acetonitrile, after 5 min. p-nitrobenzaldehyde added, and allowed to stand several min. at room temp. -> l,l-diphenyl-4-p-nitrophenyl-butatriene. Y 69%. F. e. s. K. W. Ratts and R. D. Partos, Am. Soc. 91, 6112 (1969). 

Analogously l,l-diphenyl-4,4-bis-(4-methoxyphenyl)-butatriene reacted to give 2-(p,p-di-(4-methoxyphenyl)-vinyl)-3-phenyl-indone [798]. 

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