Metal-catalyzed [2+2+2] cycloaddition is a powerful tool that allows rapid construction of functionalized 6-membered carbo- and heterocycles in a single step through an atom-economical process with high functional group tolerance. The reaction is usually regio- and chemoselective although selectivity issues can still be challenging for intermolecular reactions involving the cross-[2+2+2] cycloaddition of two or three different alkynes and various strategies have been developed to attain high selectivities. Furthermore, enantioselective [2+2+2] cycloaddition is an efficient means to create central, axial, and planar chirality and a variety of chiral organometallic complexes can be used for asymmetric transition-metal-catalyzed inter- and intramolecular reactions. This review summarizes the recent advances in the field of [2+2+2] cycloaddition.

1 Introduction

2 Formation of Carbocycles

2.1 Intermolecular Reactions

2.1.1 Cyclotrimerization of Alkynes

2.1.2 [2+2+2] Cycloaddition of Two Different Alkynes

2.1.3 [2+2+2] Cycloaddition of Alkynes/Alkenes with Alkenes/Enamides

2.2 Partially Intramolecular [2+2+2] Cycloaddition Reactions

2.2.1 Rhodium-Catalyzed [2+2+2] Cycloaddition

2.2.2 Molybdenum-Catalyzed [2+2+2] Cycloaddition

2.2.3 Cobalt-Catalyzed [2+2+2] Cycloaddition

2.2.4 Ruthenium-Catalyzed [2+2+2] Cycloaddition

2.2.5 Other Metal-Catalyzed [2+2+2] Cycloaddition

2.3 Totally Intramolecular [2+2+2] Cycloaddition Reactions

3 Formation of Heterocycles

3.1 Cycloaddition of Alkynes with Nitriles

3.2 Cycloaddition of 1,6-Diynes with Cyanamides

3.3 Cycloaddition of 1,6-Diynes with Selenocyanates

3.4 Cycloaddition of Imines with Allenes or Alkenes

3.5 Cycloaddition of (Thio)Cyanates and Isocyanates

3.6 Cycloaddition of 1,3,5-Triazines with Allenes

3.7 Cycloaddition of Aldehydes with Enynes or Allenes/Alkenes

3.8 Totally Intramolecular [2+2+2] Cycloaddition Reactions

4 Conclusion

金属催化的 [2+2+2] 环加成是一种强大的工具，可以通过具有高官能团耐受性的原子经济过程在一个步骤中快速构建功能化的 6 元碳环和杂环。该反应通常是区域选择性和化学选择性的，尽管选择性问题对于涉及两个或三个不同炔烃的交叉 [2+2+2] 环加成的分子间反应仍然具有挑战性，并且已经开发了各种策略来获得高选择性。此外，对映选择性 [2+2+2] 环加成是产生中心、轴向和平面手性的有效手段，各种手性有机金属配合物可用于不对称过渡金属催化的分子间和分子内反应。本综述总结了[2+2+2]环加成领域的最新进展。

1 简介

2 碳环的形成

2.1 分子间反应

2.1.1 炔烃的环三聚反应

2.1.2 两种不同炔烃的[2+2+2]环加成

2.1.3 炔烃/烯烃与烯烃/烯酰胺的[2+2+2]环加成

2.2 部分分子内[2+2+2]环加成反应

2.2.1 铑催化的[2+2+2]环加成

2.2.2 钼催化的[2+2+2]环加成反应

2.2.3 钴催化的[2+2+2]环加成

2.2.4 钌催化的[2+2+2]环加成

2.2.5 其他金属催化的[2+2+2]环加成

2.3 全分子内[2+2+2]环加成反应

3 杂环的形成

3.1 炔烃与腈的环加成反应

3.2 1,6-二炔与氰胺的环加成

3.3 1,6-二炔与硒氰酸酯的环加成反应

3.4 亚胺与丙二烯或烯烃的环加成反应

3.5（硫代）氰酸酯和异氰酸酯的环加成

3.6 1,3,5-三嗪与艾伦的环加成反应

3.7 醛与烯炔或​​丙二烯/烯烃的环加成

3.8 完全分子内[2+2+2]环加成反应

4。结论