http://hdl.handle.net/10366/4156 2026-04-19T17:36:54Z http://hdl.handle.net/10366/170166 [EN]A new route to racemic diethyl 2-methyl-bicyclo[3.1.1]hept-2-ene-6,6- dicarboxylate (±)-1a by means of a palladium-catalyzed intramolecular allylic alkylation exercised on malonate-ester derivatives has been developed from R-(-)-carvone. The stereocontrolled synthesis of the enantiomerically pure (-)-1b by application of a six-step reactions sequence with a 28% overall yield from acetal 8, has been accomplished. 2010-01-01T00:00:00Z http://hdl.handle.net/10366/160431 [EN]Agents that cause apoptotic cell death by interfering with tubulin dynamics, such as vinblastine and paclitaxel, are an important class of chemotherapeutics. Unfortunately, these compounds are substrates for multidrug resistance (MDR) pumps, allowing cancer cells to gain resistance to these chemotherapeutics. The indolesulfonamide family of tubulin inhibitors are not excluded by MDR pumps and have a promising activity profile, although their high lipophilicity is a pharmacokinetic limitation for their clinical use. Here we present a new family of N-indolyl-3,4,5- trimethoxybenzenesulfonamide derivatives with modifications on the indole system at positions 1 and 3 and on the sulfonamide nitrogen. We synthesized and screened against HeLa cells 34 novel indolic benzenesulfonamides. The most potent derivatives (1.7 – 109 nM) were tested against a broad panel of cancer cell lines, which revealed that substituted benzenesulfonamides analogs had highest potency. Importantly, these compounds were only moderately toxic to nontumorigenic cells, suggesting the presence of a therapeutic index. Consistent with known clinical anti-tubulin agents, these compounds arrested the cell cycle at G2/M phase. Mechanistically, they induced apoptosis via caspase 3/7 activation, which occurred during M arrest. The substituents on the sulfonamide nitrogen appeared to determine different mechanistic results and cell fates. These results suggest that the compounds act differently depending on the bridge substituents, thus making them very interesting as mechanistic probes as well as potential drugs for further development. 2024-01-01T00:00:00Z http://hdl.handle.net/10366/154289 [EN]Radical cascade cyclizations of unsaturated epoxy­nitriles induced by titanocene chloride proceed in good yields and with excellent diastereoselectivities. From three to seven stereocenters were created by the reaction and a single isomeric product was obtained from most of the substrates examined. The relative configuration of the products is consistent with cyclization occurring via a chair-like transition state. The termination of the radical cascade reaction by 4-exo, 5-exo or 6-exo cyclization onto nitrile is remarkable. 2007-01-01T00:00:00Z http://hdl.handle.net/10366/154245 [EN]A practical, short, and diastereoselective synthesis of the azadiradione BCDE fragment from a readily available starting material is described. The key step was the titanocene(III)-promoted tandem cyclization of unsaturated epoxy nitrile. 2013-01-01T00:00:00Z http://hdl.handle.net/10366/154243 [EN]Highly efficient syntheses of the anti-cancer agent trans-β-elemene have been achieved by using the readily available (±)-limonene as starting material. The syntheses were achieved in only nine to eleven steps with good overall yields. The key step in these reaction sequences is a stereoselective radical cyclization, induced by titanocene chloride. 2018-01-01T00:00:00Z http://hdl.handle.net/10366/154242 [EN]The reaction of several stereoisomeric epoxy alcohols, obtained from R-(−)-carvone, and their corresponding formates, acetates, and benzoates, promoted by Cp2TiCl has been studied. The different outcomes of the reaction of epoxy derivatives are rationalized in terms of mechanistically biased processes. The radicals emerging from oxirane cleavage provide two types of reaction: dehydroxylation (deoxycarbonylation) and dehydrogenation. The results offer considerable support for the radical elimination theory of hydroxyl, formyloxyl, and acetoxyl groups. The inability of tertiary radicals to be reduced by the Ti(III) complex is demonstrated unequivocally. 2013-01-01T00:00:00Z http://hdl.handle.net/10366/154228 [EN]A practical, brief and selective synthesis of several pinene oxide derived terpenoids can be achieved from readily available starting materials. The key step is a radical reaction promoted by titanocene chloride. 2011-01-01T00:00:00Z http://hdl.handle.net/10366/154222 [EN]A new radical clock based on pinene derivatives has been designed to measure the radical cyclization rate onto cyano and carbonyl groups and the radical elimination rate of OR and CN. In this system, the known rate constant of cyclobutylcarbinyl radical cleavage is used as the internal clock. At room temperature, the cyclization rate constants for 4-exo and 5-exo processes onto nitrile and aldehyde carbonyl groups are in the order of 107 to 108 s-¹. The radical elimination rate constants for CN, OH, OCHO, and OAc are in the order of 105 to 108 s-¹. 2008-01-01T00:00:00Z http://hdl.handle.net/10366/154213 [EN]A titanocene-mediated intramolecular radical addition of different epoxy vinyl- and allylsulfones has been achieved. Five- and six-membered ring products were obtained in good to excellent yields in the presence of both 2.2 and 0.2 equiv of Cp2TiCl. A novel double-activation strategy allowed us to achieve small-size rings such as cyclobutanes and cyclopropanes. 2015-01-01T00:00:00Z http://hdl.handle.net/10366/154211 [EN]A radical coupling reaction of diverse vinyl sulfones and epoxides was mediated by Cp2TiCl (Cp = cyclopentadienyl) to provide a straightforward synthetic pathway to hydroxy sulfones. The reaction was successfully achieved by using either an excess or a catalytic amount of the TiIII reagent. The scope of the reaction was studied for several different functionalized and substituted epoxides and vinyl sulfones. 2015-01-01T00:00:00Z http://hdl.handle.net/10366/154182 [EN]The reaction of a series of 2,3-epoxy alcohols and the corresponding formates, acetates, and benzoates promoted by Cp2TiCl has been studied. The different outcome of the reaction of epoxy derivatives has been rationalized in terms of mechanistically biased processes. After homolytic oxirane cleavage, four main types of reaction were found: dehydroxylation, decarboxylation, dehydrogenation, and deoxygenation. The reaction products varied according to the substitution pattern. The radical nature of these eliminations is demonstrated. 2010-01-01T00:00:00Z http://hdl.handle.net/10366/154181 [EN]A practical, brief and selective synthesis of limonoid CDE fragments from a readily available starting diketone is described. The key step is a cationic electrocyclization promoted by strong acids. In general the methodology has been demonstrated for compounds with sensitive furane and thiophene substituents to obtain diverse substituted indenones. Several of the compounds obtained show significant antifeedant activity against Spodoptera littoralis. 2010-01-01T00:00:00Z http://hdl.handle.net/10366/154179 [EN]Radical couplings of epoxides and nitriles mediated by Cp2TiCl provide a diastereoselective route to the synthesis of β-hydroxyketones. The conditions of this “aldol-like” reaction are mild enough to avoid the dehydration of the β-hydroxyketone. The scope of the coupling reaction with functionalized and tetrasubstituted epoxides has been studied. The radical character of the coupling reactions is demonstrated. 2009-01-01T00:00:00Z http://hdl.handle.net/10366/154148 [EN]The reactions of a series of epoxynitriles and epoxyketones induced by titanocene chloride have been studied. The kinetics of the decyanogenation of β,γ-epoxynitriles with Ti(III) corresponds to a radical reaction (k25 ≈ 106 s-1), as demonstrated by competition experiments with H-transfer from 1,4- cyclohexadiene (1,4-CHD) or PhSH or conjugate addition to acrylonitrile. The 5-exo cyclization onto nitrile induced by Ti(III) is a radical reaction (k25 ≈ 107 s-1) as seen in competition experiments with H-transfer from PhSH or the titanocene-water complex. The iminyl or alkoxyl radicals generated by 5-exo cyclization onto nitriles or ketones only undergo a reduction with Ti(III). This reaction overwhelms any alternative process, such as tandem cyclization onto alkenes or β-scission. Iminyl radicals generated by 4-exo cyclizations onto nitriles undergo reduction with Ti(III) and β-scission reaction in a ratio of 96:4 when the R-substituent is CN. Alkoxyl radicals from 4-exo cyclizations onto ketone carbonyls undergo reduction with Ti(III) and β-scission in a ratio of 60:40 when the R-substituent is COOR. In nearly all the reactions studied, the role of Ti(III) is triple: a radical initiator (homolytic cleavage of oxirane), a Lewis acid (coordination to CN or CdO), and a terminator (reduction of iminyl or alkoxyl radicals). 2007-01-01T00:00:00Z http://hdl.handle.net/10366/154147 [EN]The reductive radical cyclizations of several epoxy esters have been achieved using titanocene chloride. The tether length from the initial radical to the carbonyl acceptor is the key of the reactions. We obtained products from radical cyclization onto carbonyl formate and products from formate and hydrogen elimination. The stereochemical outcome of the 5-exo radical cyclization of two diastereomers is reported. A radical cascade cyclization of an unsaturated epoxy formate is also described. 2006-01-01T00:00:00Z http://hdl.handle.net/10366/140746 [EN] A novel approach to the production of chiral 1,3-cyclohexadienals has been developed. The organocatalysed asymmetric reaction of different β-disubstituted-α,β-unsaturated aldehydes with a chiral α,β-unsaturated aldehyde in the presence of a Jørgensen-Hayashi organocatalyst provides easy and stereocontrolled access to the cyclohexadienal backbone. This method allows for the synthesis of potential photoprotective chiral 1,3-cyclohexadienals and extra extended conjugation compounds in a simple manner. 2018-01-01T00:00:00Z