Fiorot Rodolfo G, Vilhena Felipe de S, Carneiro José W de M
Department of Chemistry, Universidade Federal Fluminense (UFF), Outeiro de São João Batista, s/n, Niterói, Rio de Janeiro, 24020-141, Brazil.
Instituto Federal de Educação, Ciências e Tecnologia do Rio de Janeiro, Rio de Janeiro, 21715-000, Brazil.
J Mol Model. 2019 Sep 7;25(10):306. doi: 10.1007/s00894-019-4162-9.
1,3-Dipolar cycloaddition (1,3-DC) reactions are powerful synthetic tool to obtain highly functionalized 5-membered heterocycles, starting from a 1,3-dipole and a dipolarophile in a single step. The reactivity of these systems is usually rationalized in terms of Frontier Molecular Orbital Theory (FMOT), which neglects a possible contribution of an open-shell weakly coupled singlet-diradical specie. In this work, the broken-symmetry approach is used to estimate the singlet-diradical character of 18 dipoles of the second period of the periodic table, classified as allyl-type N-centered, allyl-type O-centered, and propargyl-type 1,3-dipoles, providing a rationalization for 1,3-DC reactivity. The intramolecular cyclization of bent allyl-type N- and O-centered dipoles into 3-membered rings was also analyzed, and revealed that the energetic change is associated with the spin densities of peripheral atoms. Finally, a close relationship between the energy for the ring-opening process of the cyclic configuration and the reactivity of 1,3-dipoles toward 1,3-dipolar cycloaddition reaction was also found. Graphical abstract.
1,3-偶极环加成（1,3-DC）反应是一种强大的合成工具，可从一个1,3-偶极体和一个亲偶极体一步获得高度官能化的五元杂环。这些体系的反应活性通常根据前沿分子轨道理论（FMOT）进行合理化解释，该理论忽略了开壳层弱耦合单重态双自由基物种的可能贡献。在这项工作中，采用破缺对称方法来估计元素周期表第二周期的18种偶极体的单重态双自由基特征，这些偶极体分为烯丙基型N中心、烯丙基型O中心和炔丙基型1,3-偶极体，为1,3-DC反应活性提供了合理化解释。还分析了弯曲的烯丙基型N中心和O中心偶极体分子内环化为三元环的过程，结果表明能量变化与外围原子的自旋密度有关。最后，还发现了环状构型的开环过程能量与1,3-偶极体对1,3-偶极环加成反应的反应活性之间的密切关系。图形摘要。
