联烯酸酯作为C2、C3、C4合成子，在叔膦、叔胺的催化下发生形式上的[2+4]、[3+2]、[4+2]、[4+1]、[4+3]等环化时，反应的化学及区域选择性高度依赖于催化剂的结构与性质。然而，氮杂环卡宾(N-Heterocyclic Carbene, NHC)对这些反应的催化研究开展较少。我们的初步探索表明，NHC也能促进联烯酸酯与查尔酮发生[2+4]反应，构建吡喃环。与叔膦、叔胺催化的反应相比，其化学及区域选择性明显不同。本项目将研究NHC催化下联烯酸酯、带有β'-H及β'(δ)位离去基团的联烯酸酯等底物参与的串联环化反应，通过对底物和催化剂的结构与性质进行适当的调整，有望调控反应的选择性，为发现新的串联反应和控制性合成提供有效的思路和策略，为重要环状骨架的构建提供高效方法。本项目的实施将不仅凸显NHC在催化这类反应中的独特性和优越性，而且将丰富和发展联烯酸酯化学和NHC催化化学。

The tertiary amine or tertiary phosphine-catalyzed formal [2+4], [3+2], [4+2], [4+1] and [4+3] annulations involving allenoates acting as C2, C3 or C4 synthons showed that the chemical and regional selectivities of these reactions were heavily dependent on the structures and properties of catalysts. In contrast, there are only a few reports describing the catalytic effect of NHCs (N-Heterocyclic Carbenes) on these transformations. Our preliminary study showed that NHC could promote the efficient assembly of pyran through [2+4] cyclizations of allenoates with chalcones and chemical and regional selectivity of these reactions were obviously different from the system catalyzed by tertiary phosphines or tertiary amines. This project will focus on the catalytic features of NHCs demonstrated by the cascade annulations of allenoates and their derivatives bearing β'-H or β'(δ) leaving groups. We expect that the selectivities of these reactions may be tuned by the modifications of the structures and properties of substrates and catalysts, which can afford some strategies for the discoveries of new domino reactions and controllable syntheses. The fulfillment of this project will not only highlight the unique catalytic activity and efficiency of NHCs for these reactions but also provide some new facile accesses to the important heterocyclic frameworks, and enrich and develop the chemistry of allenoates and NHC catalysis.