Stereoselective Solid‐State Synthesis of Substituted Cyclobutanes Assisted by Pseudorotaxane‐like MOFs

• Published in: Angewandte Chemie International Edition Vol. 57; no. 39; pp. 12696 - 12701
• Main Authors: Hu, Fei‐Long, Mi, Yan, Zhu, Chen, Abrahams, Brendan F., Braunstein, Pierre, Lang, Jian‐Ping
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 24.09.2018; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Edition: International ed. in English
• Subjects: Chemical Sciences; Chemistry; Chemistry, Multidisciplinary; Confining; Cyclobutane; Dimerization; Dimers; Inorganic chemistry; Ligands; Metal-organic frameworks; Organic solvents; photodimerization; Physical Sciences; preorganization; regioselectivity; Science & Technology; solid-state organic synthesis; Stereoselectivity; Substitutes; Ultraviolet radiation; Zinc; regioselectivity; DIELS-ALDER; solid-state organic synthesis; 2+2 PHOTODIMERIZATION; CAVITY; ISOMERIZATION; TRANS-CINNAMIC ACIDS; DIMERIZATION; POLYMERIZATION; photodimerization; preorganization; metal-organic frameworks; DIRECTED SYNTHESIS; PHOTOCYCLOADDITION; CYCLOADDITION REACTION
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201806076

Regioselective photodimerization of trans‐4‐styrylpyridine (4‐spy) derivatives is performed using pseudorotaxane‐like Zn‐based metal organic frameworks MOFs as templates. The formation of rctt‐HT (head‐to‐tail) dimers is achieved by confining pairs of coordinated 4‐spy derivative ligands within hexagonal windows and then irradiating them with UV light. It is also possible to achieve a photodimerization reaction where two different substituted 4‐spy ligands are included in such a MOF material. The ether bond formation is employed to protect the sensitive ‐OH group of HO‐spy and the methyl group of CH3O‐spy is subsequently removed after the formation of cyclobutane derivative in the CH3O‐spy‐based MOF. Introducing substituents at the 2‐ or 3‐position of the phenyl group of 4‐spy does not significantly affect the rate of the dimerization process except in the case of the strongly electron‐withdrawing nitro group where the rate is significantly decreased. These results are in striking contrast to the mixtures of photoproducts and low yields obtained by untemplated photodimerization in organic solvents. Template synthesis: Pairs of trans‐4‐styrylpyridine or its derivatives are oriented in a parallel and head‐to‐tail (HT) manner for the solid‐state photodimerization within a pseudorotaxane‐like MOF. The high selectivity for the rctt‐HT dimers provides a controlled photodimerization within a confined environment. These results are in striking contrast to the mixtures of products and low yields obtained by untemplated photodimerization in organic solvents.