- 7Li, 31P, and1H pulsed Gradient Spin-Echo (PGSE) diffusion NMR spectroscopy and ion pairing: On the temperature dependence of the ion pairing in Li(CPh3), fluorenyllithium, and Li[N(SiMe 3)2] amongst other salts
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7Li, 31P, and 1H variable-temperature pulsed gradient spin-echo (PGSE) diffusion methods have been used to study ion pairing and aggregation states for a range of lithium salts such as lithium halides, lithium carbanions, and a lithium amide in THF solutions. For trityllithium (2) and fluorenyllithium (9), it is shown that ion pairing is favored at 299 K but the ions are well separated at 155 K. For 2-lithio-1,3-dithiane (13) and lithium hexamethyldisilazane (LiHMDS 16), low-temperature data show that the ions remain together. For the dithio anion 13, a mononuclear species has been established, whereas for the lithium amide 16, the PGSE results allow two different aggregation states to be readily recognized. For the lithium halides LiX (X = Br, Cl, I) in THF, the 7Li PGSE data show that all three salts can be described as well-separated ions at ambient temperature. The solid state structure of trityllithium (2) is described and reveals a solvent-separated ion pair formed by a [Li(thf)4]+ ion and a bare triphenylmethide anion.
- Fernandez, Ignacio,Martinez-Viviente, Eloisa,Breher, Frank,Pregosin, Paul S.
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- A SEARCH FOR SINGLE-ELECTRON TRANSFER (SET) MECHANISMS IN THE REACTION OF 1,3-DITHIANYL- AND 1,3-OXATHIANYLLITHIUMS WITH PRIMARY HALIDES
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The reaction of 1,3-dithianyl-, 2-methyl-1,3-dithianyl- and 1,3-oxathianyllithium with 6-halo-1-hexenes affords the products expected from a SN2 (rather than SET) mechanism.
- Juaristi, Eusebio,Gordillo, Barbara,Aparicio, Dulce Ma.,Bailey, William F.,Patricia, Jeffrey J.
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- Synthetic Access to the Mandelalide Family of Macrolides: Development of an Anion Relay Chemistry Strategy
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The mandelalides comprise a family of structurally complex marine macrolides that display significant cytotoxicity against several human cancer cell lines. Presented here is a full account on the development of an Anion Relay Chemistry (ARC) strategy for the total synthesis of (-)-mandelalides A and L, the two most potent members of the mandelalide family. The design and implementation of a three-component type II ARC/cross-coupling protocol and a four-component type I ARC union permits rapid access respectively to the key tetrahydrofuran and tetrahydropyran structural motifs of these natural products. Other highlights of the synthesis include an osmium-catalyzed oxidative cyclization of an allylic 1,3-diol, a mild Yamaguchi esterification to unite the northern and southern hemispheres, and a late-stage Heck macrocyclization. Synthetic mandelalides A and L displayed potent cytotoxicity against human HeLa cervical cancer cells (EC50, 1.3 and 3.1 nM, respectively). This synthetic approach also provides access to several highly potent non-natural mandelalide analogs, including a biotin-tagged mandelalide probe for future biological investigation.
- Nguyen, Minh H.,Imanishi, Masashi,Kurogi, Taichi,Wan, Xuemei,Ishmael, Jane E.,McPhail, Kerry L.,Smith, Amos B.
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p. 4287 - 4306
(2018/04/26)
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- The effect of hmpa on the reactivity of epoxides, aziridines, and alkyl halides with organolithium reagents
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A kinetic study of the effect of added HMPA cosolvent on the reaction of 2-lithio-1,3-dithiane (1), bis(phenylthio)methyllithium (2), and bis(3,5-bistrifluoromethylphenylthio)methyllithium (3) with methyloxirane (propylene oxide), N-tosyl-2-methylaziridin
- Reich, Hans J.,Sanders, Aaron W.,Fiedler, Adam T.,Bevan, Martin J.
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p. 13386 - 13387
(2007/10/03)
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- MOCVD precursors based on organometalloid ligands
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Chemical vapor deposition processes utilize as precursors volatile metal complexes with ligands containing metalloid elements silicon, germanium, tin or lead.
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- Diastereoselective synthesis of 2,3,5-trisubstituted tetrahydrofurans via cyclofunctionalization reactions. Evidence of stereoelectronic effects
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The work described herein considers the impact of stereoelectronic effects and allylic 1,3-strain in controlling the cyclofunctionalization reaction when a hydroxyl group is at the allylic position. The stereoelectronic arguments are supported by independent iodocyclization reactions performed using two secondary alcohols. The transition-state pathways involved in these reactions are established through a comparison of relative reaction rates. A bi-directional approach is used to demonstrate the potential of the iodocyclization reaction to differentiate a terminus in molecules with a pseudo C2 axis of symmetry, showing that two-directional synthesis can be used to differentiate between alternative transition-state pathways.
- Guindon,Soucy,Yoakim,Ogilvie,Plamondon
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p. 8992 - 8996
(2007/10/03)
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- Dithiane- and trithiane-based photolabile scaffolds for molecular recognition
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(formula presented) A modular synthetic approach to novel dithlane- and trithlane-based photolabile molecular hosts equipped with elements of molecular recognition is developed. The approach provides ready access to a family of amino-derivatized photocleavable molecular systems capable of hydrogen-bonding-based recognition of biologically relevant molecules, e.g., ureas, barbiturates etc. These systems undergo efficient photofragmentation in the presence of external (e.g., benzophenone) or internal (e.g., nitropyridine) electron-transfer sensitizers.
- Mitkin, Oleg D.,Kurchan, Alexei N.,Wan, Yongqin,Schiwal, Brian F.,Kutateladze, Andrei G.
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p. 1841 - 1843
(2007/10/03)
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- MOCVD precursors based on organometalloid ligands
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Chemical vapor deposition processes utilize as precursors volatile metal complexes with ligands containing metalloid elements silicon, germanium, tin or lead.
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- Substituted naphthopyrans
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Described are novel reversible photochromic 2H-naphtho[1,2-b]pyran compounds, examples of which are compounds having certain substituents at the 5 and 6-positions of the naphtho portion of the naphthopyran and at the 2-position of the pyran ring, e.g., 2,2-bis(4-methoxy phenyl)-5-methoxycarbonyl-6-morpholino-2H-naphtho[1,2-b]pyran. Certain substituents may also be present at the number 7, 8, 9 or 10 carbon atoms of the naphtho portion of the naphthopyran. Also described are organic host materials that contain or that are coated with such compounds. Articles such as ophthalmic lenses or other plastic transparencies that incorporate the novel naphthopyran compounds or combinations thereof with complementary photochromic compounds, e.g., spiro(indoline) type compounds, are also described.
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- Stereoselective Synthesis of 2Z,4E-Dienals by Addition of Organometallic Reagents to Pyrylium Perchlorate
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A facile and stereoselective approach to 2Z,4E-dienals and derived products is presented.The method involves addition of an organometallic reagent to a pyrylium salt, followed by electrocyclic ring-opening of the intermediate 2H-pyran, to give the desired Z,E-dienal, usually with greater than 95percent stereochemical purity.These dienals may be trapped in situ with a second organometallic reagent, or oxidised or redused, without loss of stereochemical integrity.The synthesis of (1,3Z,5E)-undeca-1,3,5-triene, a component of the essential oils of the brown Hawaiian seaweeds Dictyopteris plagiogramma and D. australis, is reported to illustrate the simplicity of the procedure.
- Furber, Mark,Herbert, John M.,Taylor, Richard J. K.
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p. 683 - 690
(2007/10/02)
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- REACTIONS OF METALLATED 1,3-DITHIANES WITH CARBOXYLIC ACID DERIVATIVES
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2-Lithio-1,3-dithiane and 2-lithio-2-trimethylsilyl-1,3-dithiane react with nitriles to afford primary aminoketene dithioacetals in good yields; these compounds exhibit marked ambident nucleophilicity.Use of other carboxylic acid derivatives as electrophi
- Page, Philip C. Bulman,van Niel, Monique B.,Westwood, Donald
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p. 269 - 276
(2007/10/02)
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- Branched-chain Sugars, XXIV. - Syntheses of Chain-extended and Branched-chain Sugars by Reactions with 4,5-Dihydro-2-lithio-5-methyl-1,3,5-dithiazine
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The synthesis of chain-extended sugars can be achieved by reaction of 4,5-dihydro-2-lithio-5-methyl-1,3,5-dithiazine with carbohydrates containing a primary halogen or a terminal epoxide ring.The desulfurization of these products proceeds under milder conditions than with the corresponding 1,3-dithiane adducts.Heptoses 10, 15, and 30 are obtained by this method.Sugars containing a secondary halogen form elimination products on reaction with 2. - The anion 2 seems to be slightly more reactive than 2-lithio-1,3-dithiane.
- Paulsen, Hans,Stubbe, Mathias,Heiker, Fred R.
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p. 825 - 837
(2007/10/02)
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- Prostaglandin analogues
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Prostaglandins of the formula: STR1 wherein A represents a grouping of the formula: STR2 X represents ethylene or cis-vinylene, Y represents ethylene or trans-vinylene, R represents a hydrogen atom or a straight- or branched-chain alkyl group containing f
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