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

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Reaction Steps

Thus, by forming the appropriate alkynyl salt, the length of the alkynyl moiety, represented by the value of n, incorporated into the polymer formed in step 2 can be controlled. Typically, the value of n can be varied from 1 to 12. Acetylenic derivatives having the general formula H(C≡C)nH can be readily converted into the dilithio salts by reacting with n-butyllithium. The respective dilithio salts, with values of n varying from 1 to 12, can then be incorporated into the backbone of polymers (2) as shown in the aforementioned step 2. The value of n can be varied, typically, from 1 to 12, more often from 1 to 10 and 1 to 8, most often from 1 to 6 and, in particular, from 1 to 3 and 1 to 2. Acetylenic derivatives having the general formula H(C≡C)nH can be readily formed by the synthesis given by Eastmond et al. in Silylation as a Protective Method for Terminal Alkynes in Oxidative Couplings--A General Synthesis of the Parent Polyynes, 28 TETRAHEDRON 4601 (1972). Laboratory synthesis of the lower polyyne series H(C≡C)nH (n=2,3,4 and 5) is based upon low temperature sodamide dehydrohalogenation of α,ω-bis (chloromethyl)alkynes, ClCH2 (C≡C)n-1CH2Cl in liquid ammonia, a technique which provided a convenient route to diacetylene but which proved increasingly troublesome for tri- and for tetra-acetylene. Pentaacetylene, the highest member of the series was obtained in ca 1% yield from the precursor, ClCH2 (C≡C)4CH2Cl. Polyynes in the series H(C≡C)nH (n=4,5,6,7,8,9,10 and 12) 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 Et3SiC≡CH (I)→Et3Si(C≡C)2SiEt3 (II), coupling of the silyldiyne Et3Si(C≡C)2H (III) gives Et3Si(C≡C)4SiEt3 (IV) which upon controlled cleavage yields a chromatographically separable mixture of Et3Si(C≡ C)4SiEt3 (IV) , Et3Si(C=-C)4H (V) and H(C≡C)4H (VI). Coupling of Et3Si(C≡C)4H (V) in turn gives Et3Si(C≡C)8SiEt3 (VII) which upon cleavage yields Et3Si(C≡C)8H (VIII) and H(C≡C)8H (IX) and coupling of Et3Si(C≡C)8H (VIII) gives the bissilylhexadecaacetylene Et3Si (C≡C)16SiEt3 (X) .

Provenance & Evidence