Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1985 Exploratory and mechanistic studies of cycle allene photochemistry Thomas James Stierman Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Organic Chemistry Commons Recommended Citation Stierman, Thomas James, "Exploratory and mechanistic studies of cycle allene photochemistry " (1985). Retrospective Theses and Dissertations. 12109. https://lib.dr.iastate.edu/rtd/12109 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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UniverslW MicnSilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 8524699 Stierman, Thomas James EXPLORATORY AND MECHANISTIC STUDIES OF CYCLIC ALLENE PHOTOCHEMISTRY Iowa State University PH.D. 1985 University Microfilms IntGrnâtiOnSl soon, zeeb Road, Ann Arbor, Ml 48106 Exploratory and mechanistic studies of cyclic aliéné photochemistry by Thomas James Stierman A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: .Chemistry Major: Organic Chemistry Approved: Signature was redacted for privacy. In Charge of Maiof Work Signature was redacted for privacy. Signature was redacted for privacy. For the Graduate College Iowa State University Ames, Iowa 1985 ii TABLE OF CONTENTS Page INTRODUCTION 1 HISTORICAL 2 Aliéné Triplet Reactions 2 Aliéné Singlet Reactions 8 Aliéné --Bond Rotation 15 Protic Solvent Additions to Aliénés 15 RESULTS AND DISCUSSION 21 Goals of This Research 21 Synthesis of Cyclic Aliénés 21 Singlet Photochemistry of 1,2-Cyclononadiene 22 Singlet Photochemistry of l-Methyl-l,2-cyclononadiene 51 Triplet Vapor Phase Photochemistry of Cyclic Aliénés 53 Triplet Solution Phase Photochemistry of 1,2-cyclononadiene 86 CONCLUSION 91 EXPERIMENTAL 94 General 94 BIBLIOGRAPHY 147 ACKNOWLEDGMENTS 151 1 INTRODUCTION The synthesis and ground state chemistry of aliénés have been the focus of much research and a wide variety of aliénés are readily prepared. Additionally, the photochemistry of many olefinic substrates, including simple alkenes, 1,3-dienes, and 1,4-dienes, has been intensively studied during the past three decades. In light of this, it is surprising to find that, until recently, there has been relatively few and scattered reports of the photoreactions of aliénés (i.e., 1,2-dienes). Within the past few years, however, there has been a significant effort devoted to the characterization and understanding of the photo- reactions of aliénés. A number of systems have now been examined under a variety of conditions and a rich assortment of fundamental photoreactions have been observed. As a result of these studies, our knowledge of the photoreactions of aliénés has been greatly enhanced. The purpose of this manuscript is to present the results of our studies focusing on the photoreactions of various 9-carbon ring cyclic aliénés and to briefly summarize the previous literature which is of direct significance. For a comprehensive survey of aliéné photochemistry the reader is referred to two recent reviews.1 P 2 HISTORICAL Aliéné Triplet Reactions Much of the early work in the area of aliéné photochemistry was conducted on vapor phase samples and with benzene sensitization. In 1959, Ward and Karafiath reported the most comprehensive early photochemical study of aliénés. These authors described the benzene sensitized vapor phase reactions of 1,2-hexadiene (1), 1,2- cyclononadiene (8), 1,2,6-heptatriene (11), and 1,2,6-cyclononatriene (13).3 The reactions observed are presumably due to triplet states. The benzene sensitized vapor phase photolysis of 1,2-hexadiene (1) led to the formation of four products (Scheme 1). Biradical 2 was considered to be a potential intermediate leading to the formation of 4 (via ring closure) and 5 and 6 (via fragmentation). That no cyclohexene was observed, however, led the authors to question this and arguments supporting a concerted mechanism were also presented. Bicyclohexane 7 was believed to be formed via cyclopropylidene 3. Scheme 1 H 5 (0=0.15) 4 (0=0.07) 6 (0 = 0.15) benzene vapor phase 3 7 (0 = 0.005) 3 Irradiation of 1,2-cyclononadiene (8) under similar conditions led to the formation of tricyclo[4.3.0.0^'^lnonane (10) as the sole reported product (Scheme 2).3'4 as in the reaction of 1, a cyclo- propylidene intermediate (i.e., 9) was proposed as the precursor to 10. Scheme 2 vapor phase —•0 8 9 10 (0=0.17) The photochemical behavior of unsaturated aliénés 11 and 13 was significantly different from that of saturated analogs 1 and 8.^'^ In these reactions, no evidence was found which would suggest the formation of a cyclopropylidene intermediate. The benzene sensitized vapor phase irradiation of 1,2,6-heptatriene (11) led to the formation of triene 12 as the sole reported primary product. Similarly, irradiation of 1,2,6-cyclononatriene (13) resulted in the formation of triene 14 as the sole reported primary product (Scheme 3). A concerted photo-Cope rearrangement was considered to be the most likely pathway to the observed products, although a biradical mechanism seems more consistent with the triplet multiplicity. 4 Scheme 3 ~ hv CH benzene 11 phase 12 (0=0.24) benzene vapor phase 13 14 (0=0.02) In 1981, Karan described the benzene sensitized vapor phase photolysis of cis-I,2,6-octatriene (15), a methyl-substituted derivative of 11.^ The photochemistry was considerably more complex than that reported for 11. Photolysis of cis-l,2,6-octatriene (15) led to the formation of trans isomer 16, along with six other primary products (Scheme 4). Scheme 4 // hv ^ benzene C vapor phase 16 (0=0.150) 17 (0=0.013) 18 (0 = 0.023) -CH, X 19 (0=0.006) 20 (0=0.007) 21 (0=0.042) 22 (0=0.011] 5 The major primary photoprocess was cis-trans isomerization to 16. Bicyclics 17 and 18 were viewed as arising via diradical 23 in a stepwise manner, and tricyclic 19 formation was attributed to the intermediacy of cyclopropylidene 24 (Scheme 5). The isomerization of 15 to 20 corresponds to a Cope rearrangement, in which a biradical process seems most likely to be involved. The formation of 21 and 22 can be explained either by a stepwise process involving s-homolysis or by 1,3-sigmatropic shifts. Scheme 5 // 24 19 The first report of an aliéné photolysis was by Collin and Lossing in 1957.^ Mercury photosensitized vapor phase decompositions of aliéné (25) and 1,2-butadiene (29) were reported. Irradiation of aliéné (25) led to the formation of hydrogen, a C^H^ radical, and what was believed to be 1,5-hexadiyne (28). Thus, the sole photoprocess appeared to be C-H bond hemolysis, which leads to the generation of a hydrogen atom and a C3H3 radical species (Scheme 5). The latter is believed to favor the propargyl structure (27). 5 Scheme 5 ..H hv "v c=c=c. o 'HX-C=C-H H- H' H Hg vapor phase 26 27 25 28 The major photoprocess oDserved in the irradiation of 1,2- butadiene (29) was C-C bond homolysis, which leads to the formation of methyl radicals and a C3H3 radical species (Scheme 7). No evidence for the formation of a radical, via potential C-H bond homolysis, could be found. Loss of hydrogen was observed as a minor process. Scheme 7 HjC-CHj-CSC-H 30 "\ ..'CH, c=c=c. 0 'H,C-C=C-H •CH, major 29 26 27 hv minor C,H, C2H, C4H, * H, 7 The phase dependence of aliéné triplet reactions is of interest.