Palladium(0)-catalyzed reactions of propargylic compounds with nucleophiles have been shown to be effective for the synthesis of heterocyclic compounds, [1] allylic compounds, [2] and allenes. [3] As an application of these reactions to polymer synthesis, we have reported that the palladium(0)-catalyzed polycondensation of propargylic carbonates with bifunctional nucleophiles gives exomethylene-containing polymers. [4] Recently, a palladium(0)-catalyzed coupling reaction of propargylic bis(carbonate)s with organoboron compounds has been reported by Bçhmer and Grigg, and the reaction produced diarylated dienes in moderate to good yields. [5] The results prompted us to undertake a synthetic investigation of cross-conjugated polymers by palladium(0)-catalyzed crosscoupling polymerization between a propargylic bis(carbonate) and diboron compounds. Conjugated polymers have received much attention because of their various applications such as light-emitting diodes, [6] chemical sensors, [7] and electronic devices. [8] The most studied frameworks for conjugated polymers are linearly conjugated p systems. In contrast to the conjugated polymers, cross-conjugated polymers have been less studied. However, cross-conjugated compounds have recently attracted increasing attention because of their potential for various applications. [9] For example, poly(arylene-1,1-vinylene)s are synthesized by Weber and coworkers [10] and Itami et al. [11] Cross-conjugated polymers would present new opportunities for material science.Poly(arylene-2,3-butadienylene)s, which have sequential 1,1-vinylene groups in the monomer unit, have not been reported so far. We anticipated that cross-conjugated polymers having 2,3-butadienylene moieties in the main chain would be quite interesting because the conversion of them into conjugated polymers would easily be accomplished through reactions such as the Diels-Alder reaction. This approach would be a new protocol for the synthesis of conjugated polymers. We report herein the synthesis of new cross-conjugated polymers by palladium(0)-catalyzed crosscoupling polymerization of a propargylic bis(carbonate) with diboron compounds, and their transformation into conjugated polymers.We first examined the palladium(0)-catalyzed reaction of the propargylic bis(carbonate) 1 with 3,5-dimethylphenyl boronic acid (2) as a model reaction (Table 1). The reaction of

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Das Spiel mit der Konjugation: Die Titelreaktion eines propargylischen Bis(carbonats) mit Dibor‐Verbindungen führt zu neuen kreuzkonjugierten Polymeren 1 mit 2,3‐Butadienylen‐Einheiten, die durch eine Diels‐Alder‐Reaktion in die linear konjugierten Polymere 2 umgewandelt werden können. Die cis‐verknüpften Polymere 2 zeigen in ihren Fluoreszenzspektren deutlich stärkere Stokes‐Verschiebungen als die kreuzkonjugierten Vorstufen 1.

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