The [2+2+2] cycloaddition reaction is considered one of the most efficient methods for the rapid and straightforward preparation of complex polycyclic (and heterocyclic) compounds in a highly selective and atom-economical fashion. Over the last half-century, remarkable advances in terms of chemo- and regioselectivities have been realized, endowing this reaction with attractive features as a key step in the synthesis of various biologically active molecules and materials. The development of stereoselective methodologies is more recent. In this field, asymmetric transition-metal catalysis has emerged as the most convenient tool with which to perform these [2+2+2] cycloadditions in their enantio- and diastereoselective variants. All the catalytic systems that have been developed so far are based on very close association of a transition metal (Co, Ni, Ir, Rh, ...) with a chiral ligand. The success of these reactions is then related to the reaction pattern involved (inter- and intramolecular), implying an efficient substrate/active species interaction. Thus, judicious design both of chiral ligands and of unsaturated substrates is necessary. In light of these aspects, numerous stereoselective cycloadditions have been reported; these allow the construction in one-step fashion of central, axial, planar, and helical chiralities. This review details the recent advances in this area, with specific attention to catalysts and reaction scope.

中文翻译：

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立体选择性[2+2+2]环加成的最新进展

[2+2+2] 环加成反应被认为是以高度选择性和原子经济的方式快速直接制备复杂的多环（和杂环）化合物的最有效方法之一。在过去的半个世纪里，在化学和区域选择性方面取得了显着进展，使该反应具有吸引人的特征，是合成各种生物活性分子和材料的关键步骤。立体选择性方法的发展是最近的。在该领域，不对称过渡金属催化已成为在其对映选择性和非对映选择性变体中进行这些 [2+2+2] 环加成的最方便工具。迄今为止开发的所有催化系统都基于非常紧密的过渡金属（Co、Ni、Ir, Rh, ...) 带有手性配体。这些反应的成功与所涉及的反应模式（分子间和分子内）有关，这意味着有效的底物/活性物质相互作用。因此，明智地设计手性配体和不饱和底物是必要的。鉴于这些方面，已经报道了许多立体选择性环加成；这些允许以一步方式构建中心、轴向、平面和螺旋手性。本综述详细介绍了该领域的最新进展，特别关注催化剂和反应范围。手性配体和不饱和底物的明智设计是必要的。鉴于这些方面，已经报道了许多立体选择性环加成；这些允许以一步方式构建中心、轴向、平面和螺旋手性。本综述详细介绍了该领域的最新进展，特别关注催化剂和反应范围。手性配体和不饱和底物的明智设计是必要的。鉴于这些方面，已经报道了许多立体选择性环加成；这些允许以一步方式构建中心、轴向、平面和螺旋手性。本综述详细介绍了该领域的最新进展，特别关注催化剂和反应范围。