The principle objective of this study is to conduct a definitive investigation into the cycloaddition of allenes and ketenes, with particular emphasis on halogenated ketenes.

Metal-catalyzed cycloadditions of alkynes with isocyanates or nitriles are valuable tools for the synthesis of complex carbocycles and heterocycles. Although this transformation has been studied for over three decades, the cyclizations of disocyanates with 1,3-dienes or allenes are not known and the asymmetric cycloadditions of isocyanates are scarce. To expand the scope of these powerful reactions, we studied the semi-intramolecular metal-catalyzed cycloaddition of several unsaturated systems with isocyanates. Our results show that further work in this area is needed to suppress the formation of undesired homo-coupled adducts and obtain the bicyclic products in a more efficient manner. 1,3-butadienes are versatile building blocks in organic synthesis. Therefore, it is our interest to develop an efficient method for their preparation making 1,3-butadienes more available for the organic chemist. A number of methods are known for the synthesis of these compounds, but the majority of them present problems such as poor regioselectivity, low atom economy, or require the use of toxic or non-readily available reagents. In order to develop a more effective synthesis, we employed (allenylmethyl)silanes as intermediates for the preparation of 1,3-butadienes utilizing (4-bromobut 2-ynyl)trimethylsilane as a diene equivalent. A Nozaki-Hiyama-Kishi type transformation was used for the highly regioselective preparation of (trimethylsilyl)methylallenic alcohols from aldehydes and ketones. In addition, several tridentate bis(oxazolinyl)carbazole ligands were synthesized and used for the enantioselective synthesis of allenic alcohols. Carbazole ligands synthesis was achieved by the Suzuki coupling of carbazoles with different boronic acids followed by carbonylative amidation and cyclization. We report an efficient new method for the desilylation of allenic alcohols providing a variety of secondary and tertiary 1,3-butadienylcarbinols. Furthermore, our interest in extending this methodology led us to the discovery of a novel synthesis of 2-aminomethyl-1,3-dienes from N-tosyl imines.

No description available.

<p>Cationic gold(I) complexes containing phosphine and N-heterocyclic carbene based ligands are a powerful catalysts for the hydrofunctionalization of C-C multiple bonds with carbon and heteroatom based nucleophiles as well as the cycloisomerization of enynes and related &#960;-systems. Mechanisms involving outer sphere, nucleophilic attack an activated gold &#960;-complex are typically invoked for both hydrofunctionalizations and cycloisomerizations, however, direct experimental evidence for these mechanisms remain limited.</p><p>Gold(I) catalyzed allene racemization is an important background reaction in the hydrofunctionalization of 1,3 disubstituted allenes. It can compromise chirality transfer or be exploited to realized stereoconvergent synthesis of allylic alcohols and amines. The kinetics of the racemization of aromatic 1,3-disubstituted allenes catalyzed by gold(I) phosphine complexes has been investigated. The rate of racemization displayed first order dependence on allene and gold concentration. Kinetic analysis gold(I) catalyzed racemization of allenes as a function of allene and phosphine donor ability established a depletion of electron density on the terminal allene carbons and an accumulation of electron density on the phosphine ligand in the rate-limiting transition state.</p><p>Investigation of the mechanism of gold(I) catalyzed hydrofunctionalization of allenes with alcohols, carbamates, and anilines established a variable catalyst resting state depending on the equilibrium binding affinities of the nucleophile and the relative concentrations of allene and nucleophile that are employed. Reversible C-X bond formation may explain the difference in regioselectivity observed for hydroalkoxylation and hydroamination with carbamates. Additionally, in situ analysis of the hydrofunctionalization of enatiopure 1,3-disubstituted allenes for enatiopurity of the allene and product ruled out trapping of an achiral &#951;1-intermediate and established concomitant allene racemization as the cause of loss of enatiopurity.</p><p>Finally we report the two gold(I) carbene complexes not stabilized by &#960;-conjugated heteroatoms. First, we report the hydride abstraction from a neutral gold cycloheptatrienyl complex that was isolated and characterized in solution and by single crystal X-ray diffraction. This complex represents the first example of a gold carbenoid complex that lacks conjugated heteroatom stabilization. Second we report the synthesis of the first gold(I) vinylidene via hydride abstraction from a gold (disilyl)ethylacetylide complex to form a cationic &#946;,&#946;-disilacyclopentyl vinylidene complex. The C1 and C2 carbon atoms of the vinylidene complex underwent facile interconversion presumably through the gold &#960;-disilacyclohexyne.</p> / Dissertation

Thesis advisor: James P. Morken / Described herein are methods for asymmetric allylation. Chapter 1 describes the scope of the Pd-catalyzed asymmetric diboration of prochiral allenes. The products of this process possess both a chiral allylboronate functional group and a vinylboronate moiety. The allylboronate functionality can subsequently be used for imine allylation, without isolation of the diboron intermediate, resulting in the formation of atypical allylation products through a tandem, one-pot sequence. Furthermore, enantioselection in the catalytic diboration and chirality transfer in the subsequent imine allylation are high; thus, non-racemic, protected homoallylic amines, and other derivatives, are produced in high enantiomeric excess. Chapter 2 describes the discovery and development of a transition-metal-catalyzed asymmetric conjugate allylation of allylboronate ester nucleophiles to activated enones. The scope, utility, and mechanistic aspects of this new reaction are discussed. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: James P. Morken / The first examples of an enantioselective allene diboration and diene diboration are reported. The asymmetric palladium-catalyzed allene diboration afforded 1,2- bis(boronate)esters in up to 98% ee. The reaction development for the allene diboration, as well as the expansion of the substrate scope, and elucidation of the reaction mechanism are reported. Following the development of the enantioselective allene diboration, the first enantioselective diene diboration was disclosed. 1,4-Dihydroxylation products resulting from a tandem diene diboration/oxidation sequence are obtained in up to 92% ee. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

<p>The importance of nitrogen-containing compounds in human life has drawn us to focus on the preparation of amine derivatives, combined with the limitations associated with traditional methods for the formation of C-N bonds has prompted us to develop new and efficient syntheses, of amine and ether derivatives and explore the mechanisms of the gold(I)-catalyzed reactions.</p><p>A mixture of AuCl[P(t-Bu)2o-biphenyl] (5 mol %) and AgOTf (5 mol %) served as an effective catalyst for the intermolecular hydroamination of allenes with arylamines to form N-prenylaniline and N,N-diprenylaniline derivatives. This gold(I)-catalyzed protocol was effective for the formation of arylamines at non-forcing conditions with wide substrate scope in both allene and aniline, in high yields with good regioselectivity diastereoselectivity.</p><p>The mechanism of the gold(I)-catalyzed hydroalkoxylation and hydroamination of alcohols and carbamates with allenes, catalyzed by AuIPrCl (IPr= 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgOTf was investigated. The experimental rate laws for both reactions indicate first-order behavior in nucleophile and catalyst and zero-order behavior in catalyst. We propose an outer-sphere mechanism with turnover limiting protonolysis for the gold(I)-catalyzed hydrofunctionalization of allenes with alcohols or carbamates based on kinetic isotope effect, saturation behavior, and stereochemical analysis of hydroalkoxylation.</p><p>The mechanism of gold(I)-catalyzed hydroamination of allenes with arylamines was examined. Specifically, we explored the hydroamination of 3-methy-1,2-butadiene with aniline catalyzed by AuCl[P(t-Bu)2o-biphenyl] (5 mol %) and AgOTf (5 mol %) in dioxane at 45 °C to form N-prenylaniline and N,N-diprenylaniline. The kinetics of this reaction were determined to be first-order in aniline, allene, and catalyst. We have concluded that the mechanism for the gold(I)-catalyzed intermolecular hydroamination of allenes with arylamines involves outer-sphere attack of aniline on the gold-&#61552;-allene complex based on stereochemical analysis of the hydroamination product from the reaction of an enantiomerically enriched allene, (R)-1-phenyl-1,2-butadiene, with 3-bromoaniline.</p> / Dissertation

Thesis advisor: Amir H. Hoveyda / Chapter One: Development of a New Catalytic Click Reaction Involving Nitriles and Allenes (CuPDF)Catalytic click reactions, although small in number, have made a profound impact on chemistry research, including the fields of drug discovery, biological chemistry, and materials science. What is much needed are additional catalytic reactions that bring about the union of commonly occurring and robust functional groups, are mutually orthogonal to those that exist and offer a function other than connecting two fragments. We have developed a catalytic click process that connects a nitrile and a monosubstituted allene in the presence of commercially available B2(pin)2 and a readily accessible Cu(I) complex. The modification stage involves alkene isomerization by base and condensation with a hydrazine and both processes are performed in situ. The resulting linkages contain a robust diazaborinine that is fluorescent. We demonstrate that the click process, which we have named copper(I)-catalyzed phenoxydiazaborinine formation (CuPDF) is mutually orthogonal to copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) as well as sulfur-fluorine exchange (SuFEx). These click reactions can therefore be used for efficient synthesis of sequence-defined oligomers that may contain modifiable linkages and peptide-drug conjugates. For applications in aqueous media, we have also developed, copper(I)- and palladium-catalyzed quinoline formation (Cu/PdQNF). These latter processes generate fluorescent connectors as well. Chapter Two: Development of a Catalytic Click Reaction Involving Ketones and Allenes (CuAKA) We have developed another click reaction, this time bringing about the union of a ketone and, similar to CuPDF, a monosubstituted allene and B2(pin)2. We label this click reaction copper(I)-catalyzed allene–ketone addition or CuAKA. As a consequence of shared reactants, identifying catalysts that would allow CuAKA and CuPDF to be mutually orthogonal was at the center of our investigations. Our studies resulted in the identification of copper(I) complexes that can be used to perform a click reaction on a nitrile or a ketone. Furthermore, we found that mutual orthogonality can be achieved between CuAKA and CuAAC using an amino phosphine–Cu(I) catalyst. Computational and kinetics studies were performed that shed light on the origins of catalyst-controlled chemoselectivity. Importantly, similar to CuPDF, CuAKA can be performed in aqueous media. Chapter Three: Preparation of Multi-drug Conjugates with Mutually Orthogonal Click Reactions We show that with CuAAC, CuPDF and CuAKA, three mutually orthogonal click processes can be efficiently merged to assemble complex molecules efficiently with no protection/deprotection needed. With CuAKA, similar to CuAAC and CuPDF, being also orthogonal to SuFEx, a four-armed core molecule may be used in a similar fashion. A central finding in this part of study was the discovery that CuAKA, similar to CuAAC but unlike CuPDF, can be used to link molecules that contain acidic protons, such as phenol or a carboxylic acid moieties. Chapter Four: Controlled Rupture of CuAKA-Generated Linkages A distinct attribute of CuAKA is that it forms a linkage that is cleavable under mild aqueous oxidative conditions. We show that the tertiary hydroxy group accelerates the oxidation of the nearby C–B bond within the connector to generate a -hydroxy ketone that undergoes a retro-aldol reaction to effect rupture. We show that an aryl linker between the ketone and the carrier molecule, such a bile acid or a cell-penetrating peptide (CPP) may be used to achieve the steric and electronic parameters that are needed for optimal clicking and clipping rates. To demonstrate applicability, we used CuAKA was used for efficient linking of camptothecin, an anti-cancer agent with low selectivity, to a ketone attached to unprotected penetratin, a CPP. The ensuing release of the payload proceeded readily in a 68 mM aqueous solution of hydrogen peroxide at 37 °C with control experiments indicating that a proximal lysine residue accelerates the retro-aldol reaction. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

eta2-(5-Methoxy-2-acetylphenyl)tetracarbonylmanganese (30) was reacted with 2-methyl-2-nitrosopropane (31) to form 2-acetyl-5-methoxy-N-(tert-butyl)aniline(43) in low yield. Attempts to improve the yield by varying the solvent were unsuccessful. Substrate 30 was reacted with nitrosodurene and orthomanganated triphenylphosphine sulfide was reacted with 2-methyl-2-nitrosopropane (31), however no new compounds were characterised in either case. Acetylallene (55) was reacted with 30. Electrospray ionisation-mass spectrometry(ESI-MS) provided evidence for the insertion of one and two molecules of 55 into the Mn-C bond of 30 to form the products tentatively identified as 56 and 57. The reaction of orthomanganated triphenylphosphine sulfide with acetylallene was attempted but no new compounds were characterised. In order to extend the study to ketenimines, the synthesis of the diphenylketene N-(p-tolyl)imine was attempted by the dehydration of N-(p-tolyl)diphenylacetamide under a variety of conditions, but it was not isolated in useful quantities. A single preliminary study of the reaction of diphenylketene N-(p-tolyl)imine with 30 gave an intense green solution, but no products were isolated.

This dissertation describes the investigation of the utility of metal–bis(oxazoline) complexes in catalytic asymmetric reactions. The development of Cu(II)-catalyzed regio- and enantioselective additions of silylketenthioacetals into diketones is discussed in the first chapter. \(Cu(OTf)_2(t-BuBox)\) complexes were found to be an effective catalyst with a broad substrate scope, providing tertiary alcohols in high yields, regioselectivities, and enantioselectivities. A model that accounts for the absolute stereochemistry of the product based on A1,3–interaction was proposed. Relative reactivities among diketones were also investigated. The second chapter reports the investigation of Diels–Alder reactions of N-allenoyloxazolidinones. The reaction between 3-buta-2,3-dienoyloxazolidin-2-one and cyclopentadiene was catalyzed by \(Cu(SbF_6)_2(H_2O)_2(t-BuBox)\) complexes, providing the cyclic product in high yield and enantioselectivity. The endo isomer was obtained as a major product with high selectivity. Relative reactivity between N-allenoyl oxazolidinones and unsaturated N-acyloxazolidinones was also studied. / Chemistry and Chemical Biology