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David D Díaz

Publications and source records attributed to David D Díaz.

11 recordsLinked to original sources
PubMed2006

Incorporation of 2,6-di(4,4'-dipyridyl)-9-thiabicyclo[3.3.1]nonane into discrete 2D supramolecules via coordination-driven self-assembly.

The synthesis and characterization of three new supramolecular complexes 6-8 (a rhomboid and two hexagons) via coordination-driven self-assembly are reported in excellent yields (>90%). These assemblies have 2,6-di(4,4'-dipyridyl)-9-thiabicyclo[3.3.1]nonane 2 as the bridging tecton. All assemblies were characterized by multinuclear NMR (1H and 31P), mass spectrometry (ESI-MS and ESI-FT-ICR), and elemental analysis. The X-ray structure of the 120 degrees tecton 2 is also discussed.

Bridged Bicyclo Compounds↗
PubMed2006

Synthesis of degradable model networks via ATRP and click chemistry.

A simple scheme involving atom transfer radical polymerization (ATRP) from a bifunctional initiator, conversion of the bromine end groups of the resulting telechelic polymer to azides, and cross-linking of this azido-telechelic macromonomer with multi-acetylene functionalized small molecules via copper-catalyzed azide-alkyne cycloaddition was employed to prepare the first tert-butyl acrylate model networks. This general scheme is wide in scope, enabling synthesis of model networks possessing defined pore size from any monomer polymerizable by ATRP. Introduction of an olefin moiety into the ATRP initiator enabled degradation of the materials by ozonolysis to yield star polymer products bearing three or four arms depending on which cross-linker was employed in the parent network. Size-exclusion chromatography of the ozonolysis products confirmed the pore size of the parent network and yielded insight into the number of unreacted functionalities. Model networks derived from a trifunctional alkyne were found to be more completely cross-linked than those derived from a tetrafunctional alkyne, presumably due to less steric hindrance in the former system.

Acrylates↗
PubMed2006

"Click" chemistry in a supramolecular environment: stabilization of organogels by copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition.

Organogels are thermoreversible, viscoelastic (soft) materials consisting of low molecular weight compounds which self-assemble into fibers, often of micrometer lengths and nanometer diameters. The installation of terminal azide and alkyne functional groups on the end of a standard alkylamide-based organogelator was found to cause a modest disruption in the gelation properties of the molecule. Cross-linking of those groups by the copper(I)-catalyzed azide-alkyne cycloaddition reaction produced thermoreversible materials of substantially greater gelation temperatures and mechanical rigidity. These results highlight the ability of azides and alkynes-participants in the most commonly used "click" reaction-to function as innocuous precursors to meaningful covalent interactions in materials science.

Alkynes↗
PubMed2006

[1,3]-Transfer of chirality during the Nicholas reaction in gamma-benzyloxy propargylic alcohols.

A highly regio- and stereoselective intramolecular [1,5]-hydrogen-transfer process is described. Treatment of gamma-benzyl-protected Co2(CO)6-alpha,gamma-acetylenic diols with BF3 x OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the benzyloxy group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair-like transition state substantiated by a theoretical study is also included.

Alkynes↗
PubMed2005

Fe(III) halides as effective catalysts in carbon-carbon bond formation: synthesis of 1,5-dihalo-1,4-dienes, alpha,beta-unsaturated ketones, and cyclic ethers.

Iron(III) halides have proven to be excellent catalysts in the coupling of acetylenes and aldehydes. When terminal acetylenes were used the main products obtained were 1,5-dihalo-1,4-dienes with (E,Z)-stereochemistry contaminated in some cases with (E)-alpha,beta-unsaturated ketones. The former carbonyl derivatives were the sole products isolated when nonterminal aromatic alkynes were used. When homopropargylic alcohols were used, a Prins-type cyclization occurred yielding 2-alkyl-4-halo-5,6-dihydro-2H-pyrans. In addition, anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization with homoallylic alcohols. Isolation of an intermediate acetal, calculations, and alkyne hydration studies provide substantiation of a proposed mechanism.

Journal Article↗
PubMed2004

Expanded chemistry of formamidine ureas.

[reaction: see text] Formamidine ureas display a rich manifold of reactivity. Thiols induce substitution at the carbonyl carbon to give thiolcarbamates; base-mediated alkylation and acylation occurs at the terminal urea nitrogen, and a new fragmentation/acylation pathway has been uncovered with isocyanates.

Journal Article↗
PubMed2004

Formamidine ureas as tunable electrophiles.

Formamidine urea compounds exchange imine fragments with primary nitrogen nucleophiles, allowing the preparation of a variety of derivatives from a single precursor. The reactivities of these species are governed primarily by the electron-donating power of the substituents and are tunable over a range of >10(3) in first-order rates of hydrolysis.

Journal Article↗
PubMed2003

Iron(III)-catalyzed Prins-type cyclization using homopropargylic alcohol: a method for the synthesis of 2-alkyl-4-halo-5,6-dihydro-2H-pyrans.

[reaction: see text] A new Prins-type cyclization between homopropargylic alcohol and aldehydes in the presence of FeX(3) to obtain 2-alkyl-4-halo-5,6-dihydro-2H-pyrans in good yield is described. Osmium-catalyzed cis dihydroxylation provided direct access to trans-2-alkyl-3-hydroxy-tetrahydro-pyran-4-ones. Anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization using homoallylic alcohol. Isolation of an intermediate acetal provides substantiation of a proposed mechanism.

Journal Article↗
PubMed2003

First practical synthesis of formamidine ureas and derivatives.

Isonitriles and ureas undergo a condensation reaction in the presence of acid chlorides to give formamidine ureas, for which no general synthetic routes currently exist. A mechanism is proposed in which the key intermediate is an electrophilic adduct of isonitrile and acid chloride. The process is tolerant of moderate variability in the nature of the components, and access to formamidine ureas of varying substitution patterns is further enhanced by a facile exchange reaction with amines. [reaction: see text]

Amidines↗
PubMed2003

Stereocontrolled synthesis of 1-acetylen-2,3-di-o-benzyl-tetrahydrofurans, 1,4-anhydro-arabinitol, and alpha,beta-dihydroxy-gamma-alkyl-butyrolactones.

This article describes a concise and efficient synthesis of 1-acetylen-2,3-di-O-benzyl-tetrahydrofurans from tartaric acid esters using as the key step the stereocontrolled cyclization of Co(2)(CO)(6)-complexed propargylic diols. This molecule led to enantiomerically pure 1,4-anhydro-arabinitol and alpha,beta-dihydroxy-gamma-alkyl-butyrolactones. In the latter case, the critical methylene oxidation at the oxygen vicinal position was performed by RuO(4).

4-Butyrolactone↗