The interplay between hydrogen bonding and π-π stacking interactions in the crystal packing of N1-thyminyl derivatives, and implications for the photo-chemical [2π + 2π]-cycloaddition of thyminyl compounds
作者:Priscilla Johnston、Ekaterina I. Izgorodina、Kei Saito
DOI:10.1039/c2pp25228g
日期:2012.12
The solid-state photo-chemical dimerisation of thyminyl derivatives occurs when two thyminyl units are aligned in such a way that the olefinic moieties are separated by a distance of less than 4.2 Å. When irradiated with >270 nm UV, the thyminyl olefinic groups undergo [2π + 2π]-cycloaddition to form a dimeric cyclobutane derivative. However, the design and execution of [2π + 2π]-cycloaddition reactions can be challenging due to the requirement to produce molecular crystals with the necessary olefinic alignment. In this investigation, the crystallographic and solid-state photo-chemical reactions of six N1-thyminyl derivatives are studied. Only one derivative, thyminyl propanamide (7), was found to undergo [2π + 2π]-cycloaddition in the crystalline state. As such, quantum chemical methods were employed to study the photo-chemical transition states of the derivatives, as well as the strengths of typical intermolecular interactions that were observed in their crystal structures (such as π–π stacking between the thyminyl rings, Watson and Crick style hydrogen bonding and hydrogen bonding between functional groups of N1 substituents). These results were used to rationalise the solid-state photo-reactivity of more complex bis-thyminyl monomers.
固态光化学二聚反应发生在两个胸苷单元以特定方式排列,使得它们的不饱和键之间的距离小于4.2 Å时。当用波长大于270 nm的紫外线照射时,胸苷的不饱和基团会经历[2π + 2π]环加成反应,形成二聚的环丁烷衍生物。然而,设计和执行[2π + 2π]环加成反应可能具有挑战性,因为需要制备具有必要不饱和键排列的分子晶体。在本研究中,研究了六种N1-胸苷衍生物的晶体学和固态光化学反应。仅发现胸苷丙酰胺(7)在晶体状态下经历[2π + 2π]环加成反应。因此,采用了量子化学方法研究了这些衍生物的光化学过渡态,以及在它们的晶体结构中观察到的典型分子间相互作用的强度(例如胸苷环之间的π–π堆积、沃森-克里克式氢键以及N1取代基功能团之间的氢键)。这些结果被用来合理化更复杂的二胸苷单体的固态光化学反应活性。