Pe. Eaton et al., ALKYNYLCUBANES AS PRECURSORS OF RIGID-ROD MOLECULES AND ALKYNYLCYCLOOCTATETRAENES, Journal of the American Chemical Society, 116(17), 1994, pp. 7588-7596
We have developed new methodology for the synthesis of alkynylcubanes
and have used these compounds to make rigid-rod molecules constructed
of cubane and acetylene subunits. Terminal and substituted alkynylcuba
nes 7a, 7b, 8a, 8b, 12a, and 12b were synthesized by n-BuLi-promoted e
limination of halogen from 1,1-dibromovinylcubanes 6a, 6b, and 11, fol
lowed by quenching with electrophiles. Systems with one or two acetyle
nic units between two cubanes were also prepared: dicubylacetylene (15
) was obtained via reaction of the lithium ylide of (trimethylsilyl)di
azomethane with dicubyl ketone (14); 1,4-dicubyl-1,3-butadiyne (16) wa
s made by oxidative dimerization of ethynylcubane (7a). Dimerizations
and cross-coupling reactions of various 1,4-diethynylcubanes afforded
longer rods, e.g., 1,4-bis-((trimethylsilyl)ethynyl)cubyl- 1,3-butadiy
ne (18) and rimethylsilyl)ethynyl)cubyl)-4-cubyl-1,3-butadiyne (21). R
h(I)-promoted ring opening of the cubane subunit(s) of these compounds
into the corresponding tricyclooctadiene followed by thermal rearrang
ement to the cyclooctatetraene was used to convert 7a, 8a, and 12a int
o the mono- and disubstituted alkynylcyclooctatetraenes 22a, 22b, and
23 and to take 15 and 16 into the alkynyl-bridged cyclooctatetraenes 2
4a and 24b, respectively. X-ray crystallographic analysis of 12a, 15,
16, and 18 revealed interesting details about their structures.