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The use of tris(biphenyl‐4‐yl)silyl (TBPS) as a large protecting group for polyynes has been investigated. The basic building block, TBPS–C≡C–TMS (1), is synthesized in a new “one‐pot” reaction through the sequential addition of lithiated nucleophiles to tetrachlorosilane. The TMS group of differentially protected 1 and the diyne 5 can be selectively removed in the presence of the TBPS group under mild conditions, allowing for the formation of TBPS‐endcapped di‐ and tetraynes (3 and 9) by oxidative homocoupling. For the triyne, TBPS–(C≡C)3–TMS (11), chemoselectivity for desilylation decreases dramatically, preventing formation of the corresponding hexayne. X‐ray crystallographic analysis of 3 confirms a diameter of 20 Å for the TBPS group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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Chalifoux et al. (2006) studied this question.
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