Stable monoketenes, bisketenes, polymer bound ketenes andaryl substituent effects on the ring closure of 1,2-bisketenes

This thesis describes a study of stable monoketenes, bisketenes and polymer bound ketenes. Chapter 1 is the introductory part. In this chapter, the goals of the projects are described. Chapter 2 describes the synthesis of stable unsymmetrical 1,2-bisketenes and the effects of aryl substituents on the thermal interconversion of cyclobutenediones and 1,2-bisketenes. The rates and activation parameters are reported for ring closure of 1,2-bisketenes O=C=C(C$\sb6$H$\sb4$X)C(SiMe$\sb3$)=C=O (37), generated by photolysis of the corresponding cyclobutenediones 35. The rates at 70$\sp\circ$C are correlated with the $\sigma\sb{\rm p}\sp{+}$ constant of the aryl substituents by the relationship logk = ${-}1.10\sigma\sb{\rm p}\sp{+}\ {-}3.60$ (r = 1.000). The greater reactivity in ring closure to 35 for electron-donating aryl substituents is consistent with stabilization of the electron-deficient cyclobutenedione ring by electron donor groups, and for ketene stabilization by $\pi$-acceptor groups and destabilization by $\pi$-donor groups, as has been previously postulated based on theoretical calculations. The equilibrium concentration of 37d (X = CH$\sb3$CO) was also measured and varied from 1.6% at 69.2$\sp\circ$C to 9.7% at 143.1$\sp\circ$C, exceeding by factors of 5.4-7.5 those for 37a (X = H). 2-Naphthyl substituted trimethylsilyl bisketene 81 was also made and the kinetics of ring closure of 81 to cyclobutenedione 80 were obtained. Three routes to conjugated vinylketenes are discussed in Chapter 3. Both photolytic and thermolytic ring openings of 2-trimethylsilylcyclobutenones gave stable vinylketenes. 3,6-Bis-(trimethylsilyl)-o-benzoquinone, which was expected to form a persistent vinylketene, has been synthesized. However, no ring opening product was observed upon photolysis of 3,6-bis-(trimethylsilyl)-o-benzoquinone. Instead, irradiation of 3,6-bis-(trimethylsilyl)-o-benzoquinone in CDCl$\sb3$ and in CCl$\sb4$ resulted in the formation of the corresponding catechol by hydrogen abstraction and the formation of a dimer, respectively. 3,5-Di-tert-butyl-6-hydroxy-6-methyl-2,4-cyclohexadienone and 2,4-di-tert-butyl-6-hydroxy-2,4-cyclohexadienone were made from the reaction of 3,5-di-tert-butyl-1,2-benzoquinone with CH$\sb3$Li. 6,6-Dimethyl-2,4-di-tert-butyl-2,4-cyclohexadienone was obtained from pinacol rearrangement of 3,5-di-tert-butyl-1,2-dimethyl-1,2-cyclohexanediol. The photo-isomerization of these three 2,4-cyclohexadienones has been explored. In Chapter 4, the Norrish type I cleavage of $\alpha$-silylcycioalkanones has been attempted to obtain stable ketenes. Photolysis of 2-trimethylsilylcyclohexanone with 254 nm light in benzene containing 3.5% of methanol gave a 3:2 mixture of an ester and an aldehyde, both of which were formed from the disproportionation of the biradical formed by the cleavage between C$\sb1$ and C$\sb2$. Irradiation of $\alpha$-trimethylsilyl camphor in benzene with 300 nm light gave 2,3,3-trimethyl-4-(trimethylsilylmethyl)cyclopentene and 2-(2$\sp\prime ,2\sp\prime ,3\sp\prime$-trimethylcyclopentyl)-1-trimethylsilylethenone, The latter trimethylsilyl ketene was isolated by VPC. In Chapter 5, pyrolysis of alkynyl ethers as a route to make polyketenes has been investigated. A new type of stabilized 1,8-bisketene with a phenyl spacer has been prepared for the first time. An insoluble polymer bound ketene was also prepared by pyrolysis of a polymer bound alkynyl ether, which was made from 1% cross-linked polystyrene.