Nathan L. Bauld

Hole-catalyzed and photoassisted hole-catalyzed pericyclic reactions on zeolites

Abstract The initial observations of single electron acceptor (hole) catalysis of cycloaddition reactions by zeolites are reported. Both spontaneous and photoassisted zeolite hole catalyses are observed for several conjugated organic substrates including dienes and styrenes. The zeolite hole catalyst sites are characterized as very mild in comparison to aminium salt hole catalysts and are subject to competition from Bronsted acid-catalyzed processes in some cases.

The diene component in the cation radical diels-alder

Abstract The scope of and structural constraints upon the diene component in the cation radical Diels-Alder are investigated, with special attention to electronic, steric, and conformational effects. The major factors which control the competition between Diels-Alder and cyclobutane adduct formation are also illustrated.

A two step, non-stereospecific cation radical Diels-Alder reaction

The cation radical Diels-Alder cycloadditions of cis- and trans-1-propenyl aryl ethers to 1,3-cyclopentadiene, catalyzed by tris(4-bromophenyl)aminium hexachloroantimonate in dichloromethane solution, are found to be non-stereospecific, in contrast to the stereospecificity observed in other cation radical Diels-Alder reactions previously studied. These and supporting experiments indicate that, in this particular system, the reaction occurs by a two step mechanism.

Mechanistic aspects of aminium salt‐catalyzed Diels‐Alder reactions: The substrate ionization step

Substituent effects in the aminium salt catalyzed Diels-Alder reactions of 2,3-dimethyl-1,3-butadiene with a series of meta and para substituted β-methylstyrenes are used to probe detailed mechanistic aspects of these reactions. Kinetic studies were carried out using two different aminium salt catalysts and also electrochemically, using anodic potentials corresponding to the oxidation potentials of the aminium salts. Substituent effects in the equilibrium oxidations of the styrene substrates to the corresponding cation radicals were also studied, via oxidation potential measurements. The results indicate rate determining one electron oxidation of the sytrenes to their cation radicals via an outer sphere electron transfer.

Theoretical reaction paths for cation radical cycloadditions : The [3+2] or role-reversed cation radical diels-alder

Abstract An extended basis set ab initio reaction path calculation for the prototype role-reversed cation radical Diels-Alder reveals that even this symmetry-forbidden cyclization mode proceeds without activation, at least in the gas phase. An intermediate, termed a long-bond complex, is encountered on the path, but the energy minimum is so shallow that the reaction is considered likely to be concerted when entropy effects are considered. The calculation further reveals that the factor which importantly distinguishes the role-reversed cycloaddition mode from the allowed cycloaddition mode, namely, the presence of charge predominantly on the diene moiety as contrasted to the dienophilic moiety, is maintained well along the reaction path and even in the long-bond intermediate. Competition between the role-reversed Diels-Alder and a competing [2+1] cyclobutane cycloaddition is envisioned.

Polymers for catalytic cation radical chemistry

Abstract Cation radical polymers which have cation radical functions at up to 5% of the poly(styrene) monomer sites have been prepared, and their effectiveness in catalyzing the cation radical Diels-Alder reaction is demonstrated.

Block and Random Living, Ring‐Opening Metathesis Copolymerization of Functionally Differentiated Carbazole‐Containing Norbornene Monomers

The synthesis of novel diblock polymers containing both a potential charge transport and a non-linear optic block has been accomplished. The synthesis exploits the living, ring-opening metathesis block copolymerization of two norbornene type monomers, one of which contains an unsubstituted N-carbazolyl ring while the other has a bromo substituent at the 3-position of the carbazole ring. Conversion of the bromo functionality to a 2,2-dicyanovinyl group introduces the non-linear optic property. The first monomer was prepared by the previously reported efficient cation radical Diels–Alder cycloaddition of N-trans-1-propenylcarbazole to 1,3-cyclopentadiene, while the second was obtained by N-bromosuccinimide bromination of the first monomer. For purposes of comparison, the corresponding random copolymer was also synthesized.

The intramolecular cation radical diels-alder reaction

Abstract The first examples of intramolecular cation radical Diels-Alder reactions have been established using trienes which cyclize to hydroindane systems. The extremely high endo stereoselectivity characteristic of the cation radical Diels-Alder reaction is effectively exploited to generate trans -hydroindanes with high selectivity.

A New and Efficient Synthesis of Enamido Dienes and Dienamido Olefins for Intramolecular Diels-Alder Additions Leading to Hydroquinolones and Alkaloids

Abstract The enamido or dienamido functionality is directly and efficiently introduced into a bifunctional or more general context by alkylation of the previously unreported enolates of enamides or dienamides. These alkylations provide an extremely convenient method for the synthesis of bifunctional enamido dienes and dienamido olefins, both of which are readily converted to hydroquinolones by intramolecular Diels-Alder cycloaddition.

An Efficient Synthesis of Ring‐Opening Metathesis Monomers and Polymers Containing Carbazole and Other Electron‐Rich Moieties

An efficient synthesis of ring-opening metathesis monomers and polymers containing ionizable moieties such as N-carbazolyl, 2-dibenzofuranyl, 2-dibenzothiophenyl, and 4-anisyl functionalities has been developed, using cation radical Diels-Alder cycloaddition chemistry to generate the appropriate norbornene-type monomers.