Structure and Photochemical Properties of r-l, c-2, t-3, t-4-1,3-Bis[ 2-( 5- R- benzoxazolyl ) ]-2,4-di( 4- R'- phenyl ) cyclobutane

• 来源期刊: 中国化学（英文版）
• 学科: 化学
• 年，卷（期）: 2001,（7）
• 所属期刊栏目: Articles
• 页码范围: 695-701
• 页数: 7页
• 分类号: O6
• 语种: 英文

摘要

r-l, e-2, t-3, t-4-1,3-Bis [ 2- (5-R-benzoxazolyl) ]-2, 4-da (4-R'phenyl)cyclobutane (Ha: R=R'=H; Ⅱb: R--Me, R'=H;Ⅱc: R=Me, R' =OMc) was synthesized with high stereo-selectivity by the photodimerization of trans-l-[2-(5-R-benzoxazolyl)]-2-(4-R'-phenyl)ethene (Ia: R=R'=H; lb: R=Me,R'=H; Ic: R=Me, R'=OMe) in sulfuric acid. TThe structmres of Ⅱa-—Ⅱc were identified by elemental mnalysis, IR,UV, 1H NMR,13C NMR and MS. The molecular and crystalstrncture of Ⅱc has been deternmined by X-ray diffractionmethod.The crystal of Ⅱc (C34H30N2O4 .0.5C2H5HH) ismonoclinic,space group p21/n with cell dimensins of a =1.5416(3), b = 0.5625(1), c=1.7875(4) mn, β = 91.56(3)°, V=1.550(1) mn3, Z--2. The structure shows that themolecule of Ⅱc is centrosymmetric, which indicates that thedimerizaion process is a head-to-tmail fashion. The selectivityof the photodimerization Ia--Ic has been enhanced by usingacidic solvent amd the reaction speed would be decreased whenelecton donating group was introduced in the 4-position of thephenyl group. That the photodimerization is not affected bythe presence of oxygen as well as its high stereo-selectivitydemonstrated that the reaction thoceeded an exaltedsinglet. It was also found fund that under irradiation of slortwavelength UV, these dimers underwent photolysis comp1etelyto reproduce its trans-monomers, and then the new formedspecies changed into their cis-isomers through trans-cis isomerzation.