Terrence J. Connolly

Photochemical synthesis of TEMPO-capped initiators for “living” free radical polymerization

Abstract Two photochemical routes to stoichiometric initiators used in living free radical polymerizations are presented. These routes offer the advantages of higher yields and allow for the preparation of initiators not accessible using current methodology. All initiators gave detectable carbon centered radicals (laser flash photolysis) and promoted the polymerization of styrene.

Reactions of the “stable” nitroxide radical TEMPO. Relevance to “living” free radical polymerizations and autopolymerization of styrene

Abstract The stable nitroxide TEMPO is shown to react with styrene and polystyrene models under conditions typically used for polymerizations. These results show that the nitroxide is not inert at the elevated temperatures necessary to conduct polymerizations. The implications of hydrogen abstraction and olefin addition by the nitroxide are discussed, particularly as they apply to initiation, control of polydispersity and nitroxide mediated autopolymerization of styrene.

Photochemically generated bicyclic ortho-quinodimethanes: Photo-enolization of bicyclic aldehydes and ketones

Abstract A photoenolization route to bicyclic ortho -quinodimethanes was investigated. Bicyclic photoenols were trapped in an intermolecular fashion with various dienophiles for the first time. All ortho -quinodimethane precursors were prepared via a selective route commencing with 1-indanol, α-tetralol and 1-benzosuberone. Irradiation afforded the E -photoenols exclusively which were trapped with equal efficiency except that derived from indane-4-carboxaldehyde. This low efficiency has been ascribed to rapid auto-oxidation of the aldehyde to carboxylic acid. The facial selectivity of the reaction between the photoenol from benzosuberan-9-carboxaldehyde and dimethyl fumarate was much lower when compared to the other aldehydes in this study. A distorted diene caused by the presence of the seven membered ring explains these results.

The synthesis of sultines from δ-hydroxy sulfoxides revisited

Abstract A re-examination of a previously thought general synthesis of sultines from δ-hydroxy sulfoxides is shown to be more complicated than originally believed. The products obtained can be α,α′-dihaloxylenes or δ-halosulfones. The results are best interpreted based on carbocation stability of the key oxo-sulfoxonium salt intermediate.

The thermolysis and photochemistry of hybrid initiators for ‘living’ free radical polymerization

Abstract A new initiator potentially capable of both thermal and photochemical initiation of ‘living’ free radical polymerization (LFRP) has been prepared. Both of these reaction pathways have been examined and identified in terms of their products. The thermal reaction is highly dependent on the reaction conditions and displays competitive radical and ionic reactivity. In the presence of a proton source, the ionic pathway is highly favored. Photochemical activation leads predominantly to Norrish type I cleavage where the photoproducts further react by α-cleavage resulting in the formation of benzaldehyde.

Trapping of photogenerated group IV radicals by TEMPO: Potential new organometallic initiators for “living” free radical polymerization

A series of trialkyl and triaryl organometallic radicals from group IV generated by hydrogen abstraction by tert-butoxyl radical from the parent hydrides have been examined using laser flash photolysis. The rate constants for the trapping of the metal-centered radicals by the persistent radical TEMPO were measured and were found to be large and similar to those of the carbon-centered radical systems, yet below the diffusion controlled limit. The metal-centered radicals were found to be efficiently trapped by TEMPO and would appear to be candidates suitable for “living” free radical polymerization similar to carbon analogue stoichiometric initiators. The radical trapping rate constants for the trialkyl series (M = Si, Ge, Sn) were found to be 8.9 × 108 M−1 s−1 (M = Si), 7.2 × 108 M−1 s−1 (M = Ge), and 6.2 × 108 M−1 s−1 (M = Sn), respectively. The triaryl (Ph3M•) series gave slightly slower rates of 1.6 × 108 M−1 s−1 (M = Si), 3.4 × 108 M−1 s−1 (M = Ge), and 1.9 × 107 M−1 s−1 (M = Sn), respectively.

The synthesis of bicyclic ortho-quinodimethanes from tricyclic sulfones

Abstract The first synthesis of bicyclic ortho-quinodimethanes from tricyclic sulfone precursors has been achieved. The required sulfones, 3,4,5,6-tetrahydro-1H-cyclohex[cd]benzothiophene-2,2-dioxide and 1,3,4,5,6,7-hexahydrocyclohept[cd]benzothiophene-2,2-dioxide, were prepared from α-tetralone and benzosuberone utilizing a ring closure proceeding through a sulfonium salt intermediate. The same strategy failed when trying to prepare the tricyclic sulfone of the indane series. Other contrasting reactivity was also noticed when comparing the ability and ease of formation of tricyclic ether compounds. These results indicate that the later ring system is considerably strained.