Coordination Polymer-mediated Stereoselective Control Of [2+2] Photocycloaddition Reaction

The cyclobutane is an important structural motif in natural products and pharmaceutical molecules and an essential building block for numerous organic reactions.[2+2]photocycloaddition reactions represent the most straightforward and atom-economical approach for constructing cyclobutanes.The structural and functional adjustability of coordination polymers（CPs）can serve as reaction platforms for solid-state[2+2]photocycloaddition reactions.With proper design,the regional and stereoselectivity of the reactions can be improved.In this paper,the stereoselective synthesis of various cyclobutane derivatives was achieved with the coordination polymers as the reaction platform,by the coordination guiding effects and external stimulus to precisely control the[2+2]photocycloaddition reaction.The main researches are as follows:1.Four structurally diverse coordination polymers CP₁–CP₄ were designed and constructed from Cd（Ⅱ）ions and dicarboxylate ligands with different shapes（“V”/linear）and the alkene containing monomer CH₃-bpeb.The structural differences of the four coordination polymers were determined by the geometry and proportion of the dicarboxylic acid ligands.In CP₁–CP₄,pairs of CH₃-bpeb molecules were arranged at an appropriate distance and orientation by the coordination guiding effects of Cd and carboxylic acid for the stereoselective control of[2+2]photocycloaddition reaction.Finally,CP₁-CP₄ could all synthesize monocyclobutane compounds with specific configuration through light reaction.2.A temperature-sensitive chain coordination polymer CP₅ was constructed from Cd（Ⅱ）metal salts,5-F-1,3-bpeb monomers and para-fluorobenzoic acids.In CP₅,a pair of 5-F-1,3-bpeb was arranged in a face-to-face style.Through the photo/thermal effect,the[2+2]photocycloaddition reaction and the cyclocleavage reaction were precisely controlled.Five cyclobutane isomers（CP₅-1,CP₅-1’,endo,endo-CP₅-2α,exo,endo-CP₅-2β,and exo,exo-CP₅-2γ）were stereoselectively produced.These isomers could be interconverted inside CP₅ via cutting/coupling specific bonds,which could be regarded as a type of molecular surgery.3.The compound 4-[2-（4-pyridine）vinyl]benzoic acid（Hpya）containing photoactivity C=C was used to construct a coordination template with Cd（Ⅱ）ions.Using the template,four monoene ligand were encapsulated and CP₆ and CP_6X（X=a,b,c）were obtained.Four heterocyclobutane compounds(CP₆-1 and CP_6X-1（X=a,b,c）)were synthesized by the[2+2]photocycloaddition through the guiding role of the template.On the basis,using the photostable C≡C to replace the C=C in the template to shield the photoreactivity of the template.Then used it to encapsulate three monoene ligands,which formed CP_7X（X=a,b,c）.In this way,the synthesis of the head-to-head homologous cyclobutane compounds(CP_7X-1（X=a,b,c）)was realized after[2+2]photocycloaddition reaction.In this work,high stereoselective synthesis of cyclobutane compounds was achieved through stereoselective control of[2+2]photocycloaddition reaction induced by photoactivity difference.