1,3,5,7-Octatetrayne → HCID 15510876, compound

Participants

Reaction Steps

Acetylenic derivatives having the general formula H—(C≡C)m—H can be formed by the procedure disclosed in Eastmond et al., “Silylation as a Protective Method for Terminal Alkynes in Oxidative Couplings—A General Synthesis of the Parent Polyynes,” Tetrahedron, 1972, 28, 4601, incorporated herein by reference, and can be converted into dilithio salts by reacting with n-butyllithium. Synthesis of the lower polyyne series H—(C≡C)m—H (n=2, 3, 4 and 5) is known to be based upon low temperature sodamide dehydrohalogenation of α,ω-bis(chloromethyl)alkynes, ClCH2—(C≡C)m−l—CH2Cl in liquid ammonia, a technique which provided a convenient route to diacetylene but which proved increasingly troublesome for tri- and tetraacetylene. Pentaacetylene, the highest member of the series was obtained in ca. 1% yield from the precursor, ClCH2-(C≡C)4—CH2Cl. Polyynes in the series H—(C≡C)m—H (n═4, 5, 6, 7, 8, 9, 10 and 12) are known to have been prepared in solution by sequences involving Cu-catalyses oxidative couplings (Hay technique) of silyl-protected terminal alkynes, partial cleavage (desilylation) of the products by alkali, recoupling and complete desilylation. Thus using conditions established in a model coupling Et3Si—C≡C—H (I)→Et3Si—(C≡C)2—SiEt3 (II), coupling of the silyldiyne Et3Si—(C≡C)2—H (III) gives Et3S—(C≡C)4—SiEt3 (IV) which upon controlled cleavage yields a chromatographically separable mixture of Et3S—(C≡C)4—SiEt3 (IV), Et3Si—(C≡C)4—H (V) and H—(C≡C)4—H (VI). Coupling of Et3Si—(C≡C)4—H (V) in turn gives Et3Si—(C≡C)8—SiEt3 (VII) which upon cleavage yields Et3Si—(C≡C)8—H (VIII) and H—(C≡C)8—H (IX) and coupling of Et3Si—(C≡C)8—H (VIII) gives the bissilylhexadecaacetylene Et3Si—(C≡C)16—SiEt3 (X).

Provenance & Evidence