Title STUDIES ON PHOTOCHEMICAL REACTIONS OF SIMPLE ALKENES Author(s) 井上, 佳久 Citation Issue Date Text Version ETD URL http://hdl.handle.net/11094/1547 DOI rights Note Osaka University Knowledge Archive : OUKA https://ir.library.osaka-u.ac.jp/ Osaka University STUDIESON PHOTOCHEMICAL REACTIONS CF SIMPLE ALKENES YOSHIHISA INOUE OSAKA UNIVERSITY OSAKA, JAPAN JANUARY, 1977 ii Preface The work of thi's•theSis 'was performed under the guiqance of Professor Hiroshi Sakurai at the ZnstituteofScientific and lndustrial Research, Osaka University. I arn deeply grateÅíul to Professor Hiroshi Sakurai for his appro- priate guidance and continuOus encouragernent throughout this work since 1972. : am aiso grateful to Professor Yoshinobu Odaira-who initiated me into the organic photochemistry in 1971-1972. : arn indebted to Assistant Professor Setsuo Takamuku for his invaluable discussions throughout the work. Many thanks are given to Drs. Yoshiki Okarrtoto, Chyongjin Pac, Susumu Toki, and Yasuo Shige- mitsu for their helpful suggestions through the stimulating discussions with me. T would like to express my gratitude to Mr. Kazuyoshi Mori- tsugut Mr. Masahiro Kadohira, and Ms. Yoko Kunitomi for their collabo- rations in the course of experiment. Finally I wish to thank all the members of Sakurai Laboratory for their warm friendship. t- ..<2IZI Yoshihisa Inoue Suita, Osaka January, Z977 iii List of Papers The contents of this thesis are composed of the following papers. 1) Mercury Photosensitized Rbaction of Cycloheptene. Mechanism of Norcarane Formation Y. Tnoue, M. Kadohira, S. Takasnuku, and H. Sakurait Tetrahedron Lett., 459(1974). 2) Vapor-phase Photolysis of cis-- and trans-4i5-Diraethylcyclohexenes Y. rnoue, S. Takagtuku, and H. Sakurai, Bull. Chern. Soc. Jpn., 48, 3101(1975). 3) PhotochemicaZ Rearrangement of Cycloheptene Y. Inoue, S. Takamuku, and H. Sakurai, J. Chern. Soc. Chera. Cornm., 577(1975). 4) Intramolecular Hydrogen Abstraction of the Vibrationaliy Excited Triplet State of Simple Aikenes Y. :noue, S. Takarnu]gu, and H. Sakurai, J. Chem. Soc. Chem. Comm.t 896(l975). 5) Sensitized Photolysis of cis-Cyclooctene Vapour Y. rnoue, K. Moritsugu, S. Takarnuku, and H. Sakurait J. Chem. Soc. Perkin II, 569(l976). 6) Vapor-phase Photolysis of cis-Cyclononene Y. Inoue, S. Takamuku, and H. Sakurai, Bull. Chem. Soc. Jpn., 49, U47(l976). 7) An Anomalously High trans:cis Photostationary'Ratio on the Direet Photo- isomerization of Cyclooctene Y. Znoue, S. Takamuku, and H. Sakurai, J. Chern. Soc. Chem. Comm.t 423(1976). 8) Mercury Photosensitization of 1-Hexene and cis-2-Octene Vapor. Zntramolecular Hydrogen Abstraction of Vibrationally Excited T,lr* Triplet State Y. !nouer S. Takarnuku, and H. Sakurait Can. J. Chem.,EILt, 3117(1976). 9) Direct and Sensitized cis-trans Photoisomerization of Cyclooctene. Effects of Spin Multiplicity and Vibrational Activation of Excited States on Photo-- stationary translcis Ratio Y. Inoue, S. Takamuku, and H. Sakurai, J. phys. Chem., in press(January, 1977)r IO) Direct Photolysis of Cycloalkenes Y. Inoue, S. Takarriuku, and H. Sakurai, J. Chem. Soc. Perkin Ir, in press. Il) Direct cis-trans Photoisomerization of Cyclooctene. A Convenient Method for Preparing trans-Cyclooctene Y. :nouet S. Takarnuku, and H. Sakurai, Synthesis, in press. iv Contents Zntroduction 1 Chapter Z Direct Photolysis of Cycloalkenes 4 Experimental 5 Results 8 Discussion 14 Chapter 2 Sensitized Photolysis of Simple Alkenes: rntramolecuiar Hydrogen Transfer of Vibrationally Excited T,Tt TripZet State 2-1 Triplet Sensitization of Cycloalkene Vapor 22 Experimental 22 Results 24 Discussion 27 2•-2 Triplet Sensitization of Acyclic Alkene Vapor 36 Experimental 36 Results 38 Discussion 41 Chapter 3 Comparison of Direct and Sensitized Photolysis: Effects of Spin Multiplicity and Vibrational Activation 3-1 Vapor--Phase PhotolysiS Of cis- and trans-4,5-Dirnethyl- cyclohexenes 48 Experimental 48 Results 51 Discussion 54 3-2 Direct and Sensitized cis-trans Photoisomerization of Cyclooctene: Effects of Spin Multiplicity and Vibra- tionaJ Activation of Excited States on the Photosta- tionary trans/cis Ratio 60 Experimental 60 Results 62 Discussion 65 Conclusion 72 ]- Introduction Progress has been rapid in organic photochemistry during the last two decades. The selective introduction of energy into individual molecule by means of absor]ption of light provides a unique approach to effecting. chemical transforrnations in organic molecules, and a wide variety of new photo-induced reactions, which are of importance in both synthetic and mechanistic aspects, has come to our knowledge. The rapid accurnulation of the knowledge in organic photochemistry makes possible the systernatic interpretation of the photochemical reactions particularly of aromatic and carbonyl compounds. Recent interest in photocheraistry rnay be found in the further understanding of the correlation between the electronic states involved and their chemical reactivities. Although, with the complicated electron-systems containing various excited states, such discussions have actually made, the detailed investigations with more simplified electronic systems.are desired in order to further clarify the electronic state-reactivity relationship. Ethylene and its alkyl--derivatives, which are at the foundation of our understanding of unsaturated corapeunds, provide a suitable system for investigating the photochernical behaviors of pure, simplest 2T-electren system. Considering the fundamental position of these sirnple alkenes, it is surprising,that little effort has been directed teward the systematic understanding of their photochernical reactivities, although the photo- physics of these molecules have rather been known (see below). Energetics and Dynamics - ill98!E;caiirnoi Ry 1 Emission rare(SltTl); ÅëF,S!Sp<O.Ol sl,v140 Åëew<ool 2 Large SrTi separation; Åë <O.Ol S.T .- 8 3 Rapid torsional rctotion for Slt Tl hv Tl s: 4 Rapid internal conversion(Sl-,G:) hV (sens) 5 Rydberg excited state(Ry); Se little information Ethylene Fig. 1. Photophysics of Simple Alkenes 2 il 'O,OJ.O.',ol Ethylene i.ooo l .t ' ftepene 10,Ooo Bvtene-t 10,OOO Penlene.1 IO,OOO - E c;s- eutet}e-2 " iqeoo k -OE cis.-Ptntene-2 to,ooo N., 2 ttans•Bgtefie-2 IO,Ooo == v trons-PentefiS-2 . ., IO,OOO x =s 2•-methvl propeni to,ooo 'g' l, g 2-methgl bete"e-2 lo.ooo e , g 2-methyt por,tette-2 10,OOO E 3-metbyt trens-petTtet,e-2 IO,OOO l 2:3 -aimethpt tuene-2 i?Jo,gO,1 IOOS l6oo 20oo 24eo Wdvelength . in Angstr6ms Fig. 2. Far-ultraviolet spectra of some simple alkenes; L. C. Jones, Jr. and L. W. Taylor, Anal. Chera.t 27, ?78(l955) . This is partly due to the absence oE the effective absorption band in an accessible uv region above 230 nmt as shown in Fig. 2. rn view of the present situation of the alkene photochemistryi it is not only vaiuable to investigate and systematize the photochernistry of simple alkenes, but such studies wiZl also provide beneficial informations for discussing the photochemical reactions of other unsaturated compounds. One of the main intentions of this thesis is to reveal the chernical reactivities of the electronically excited states generated in'the direct and sensitized photolyses of simple alkenes. Eurtherrnore, the auther wishes to discuss the effects of spin states and vibrational..activation of the excited states on their rectivities. Chapter l deals with the direct photolysis at l85 rm of cyeloalkenes (C6-Cg) in the vapor and liquid phases. The chemical behaviors of T,Tt excited singlet and T,R(3s) Rydberg state wili be clariEied. A synthetic application of the direct photolysisisalso described. Chapter 2 deaZs with the photosensitized reaction of simple alkenes(C6-Cg) in the vapor 3 phase. Novel reactions via vibrationally-excited triplet state and their dbtailed mechanism will be described. Zn connection with the elecronic state-readtivitY relationship, Chapter 3 deals with the com- parative studies of direct and sensitized photolyses. Zn the first section of the chapter, the• emphasis will be piaced on the spin correla- tion effects on the stereochemistry of ,ithe reaction andalso on a "hott triplet" 'biradical interrnediate generated on vapor-phase photosensitiza- tion. The second section deals with the photochemical cis--trans isomeri- zation of cyclooctene. The drastic effects ofi spin multiplicity and vibrationai activation on the photostationary state of cyclooctene will be discussed, 4 Chapter l Direct Photolysis of Cycloalkenes While a variety of studies has been made on the photochemistry of alkyl-- substitutedethylenes, the great majority of these works concerned with the triplet sensitization and therefore with the chemical reactivities of the alkene,•triplet thus generated. On the other hand, photoche:ttical behaviors following direct excitation of these compounds are known iess, partiy be- cause of the absence of the effective absorption in the uv region above 230 rm. Lirnited studies on the vapor-phase photolysisl have shown that, when directly irradiated, an alkene is promoted to an excited singlet state and then suffers fast internal conversion to afford a vibrationally excited ground-state molecule; this species is known to undergo the allylic C-C and/or C-H bond cleavages in addition to the cis-trans isomerization by collisional deactivations. On liquid-phase direct photolysis, apart frorn the cis-trans isomerization and the allylic fissions, the stereospecific cyclodimerization of 2--butene2 and the photorearrangements via carbene interrnediates of tetrasubstituted alkenes