Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Tether formation

A solution of methyl 4-hydroxybut-2-enoate 3 (20 mg, 0.17 mmol) in pyridine (1.5 mL) was added to a solution of anthrone 50 (33 mg, 0.17 mmol) and PhB(OH)2 (22 mg, 0.18 mmol) in pyridine (1.5 mL). The resulting solution was then heated at reflux for 5 h with azeotropic removal of H2O. Removal of the solvent in vacuo and purification of the residue by preparative thin layer chromatography (hexane/EtOAc, 3 1) provided the Diels-Alder adduct 51 (55 mg, 81%), m.p. 218 °C. [Pg.386]

3 Use of the (Bromomethyl)dimethylsilyl Ether Group in a Radical Cyclization in the Synthesis of Talaromycin A, 140 [54] [Pg.386]

Et3N (40 pL, 0.29 mmol) and imidazole (20 mg, 0.29 mmol) were added to a solution of (4R,8R)-8-ethyl-4-hydroxy-l,7-dioxaspiro[5.5]undec-2-ene (38 mg, 0.29 mmol) in DMF (2 mL) and the resulting solution was stirred for 5 min. (Bromomethyl)dimethyl-silyl chloride (40 pL, 0.29 mmol) was then added and the reaction was stirred for 3 h. The reaction was quenched by the addition of NaHC03 solution (satd) and diluted with Et20. The organic layer was washed with brine, dried (MgS04) and then concentrated in vacuo. Purification of the residue by flash column chromatography (EtOAc/hexane, 1 1) provided the silyl ether 139 as a labile, colorless oil (62 mg, 93%). [Pg.386]


Li Z, Anvari B, Takashima M, Brecht P, Torres JH, Brownell WE (2002) Membrane tether formation from outer hair cells with optical tweezers. Biophys. J. 82 1386-1395. [Pg.371]

In the cases of dimethylsilyl IMDA precursors, the exolendo selectivity was poor. However, this ratio could be readily and quite dramatically influenced by varying the alkyl substituents on the silicon template [12]. Thus with dienol 24, tether formation with dimethylvinylsilyl chloride and subsequent IMDA reaction afforded a 4 1 mixture of exolendo products (Scheme 10-7). The ratio could be further improved to 10 1 by using a diphenylsilyl tether, and when bulky Bu groups were used, a single stereoisomer, resulting from exo addition, was observed. This example once more illustrates the potential for tuning the stereoselectivity of the reaction by varying the steric interactions with the tether. [Pg.283]

Bo, L. and Waugh, R.E. Determination of bilayer membrane bending stiffness by tether formation from giant, thin-walled vesicles, Biophys. /., 55, 509,1989. [Pg.1058]

Seitz M ef al 1998 Formation of tethered supported bilayers via membrane-inserting reactive lipids Thin Solid Films 327-9 767-71... [Pg.1749]

Fig. 4. Atom manipulation by the scanning tunneling microscope (STM). Once the STM tip has located the adsorbate atom, the tip is lowered such that the attractive interaction between the tip and the adsorbate is sufficient to keep the adsorbate "tethered" to the tip. The tip is then moved to the desired location on the surface and withdrawn, leaving the adsorbate atom bound to the surface at a new location. The figure schematically depicts the use of this process in the formation of a "quantum corral" of 48 Fe atoms arranged in a circle of about 14.3 nm diameter on a Cu(lll) surface at 4 K. Fig. 4. Atom manipulation by the scanning tunneling microscope (STM). Once the STM tip has located the adsorbate atom, the tip is lowered such that the attractive interaction between the tip and the adsorbate is sufficient to keep the adsorbate "tethered" to the tip. The tip is then moved to the desired location on the surface and withdrawn, leaving the adsorbate atom bound to the surface at a new location. The figure schematically depicts the use of this process in the formation of a "quantum corral" of 48 Fe atoms arranged in a circle of about 14.3 nm diameter on a Cu(lll) surface at 4 K.
Intramolecular cycloadditions of substrates with a cleavable tether have also been realized. Thus esters (37a-37d) provided the structurally interesting tricyclic lactones (38-43). It is interesting to note that the cyclododecenyl system (w = 7) proceeded at room temperature whereas all others required refluxing dioxane. In each case, the stereoselectivity with respect to the tether was excellent. As expected, the cyclohexenyl (n=l) and cycloheptenyl (n = 2) gave the syn adducts (38) and (39) almost exclusively. On the other hand, the cyclooctenyl (n = 3) and cyclododecenyl (n = 7) systems favored the anti adducts (41) and (42) instead. The formation of the endocyclic isomer (39, n=l) in the cyclohexenyl case can be explained by the isomerization of the initial adduct (44), which can not cyclize due to ring-strain, to the other 7t-allyl-Pd intermediate (45) which then ring-closes to (39) (Scheme 2.13) [20]. While the yields may not be spectacular, it is still remarkable that these reactions proceeded as well as they did since the substrates do contain another allylic ester moiety which is known to undergo ionization in the presence of the same palladium catalyst. [Pg.65]

Cyclizations of A-acyliminium ions containing a 3-alkenyl substituent tethered to nitrogen usually proceed with preferential formation of a six-mentbered ring via a chair-like transition state, if the alkene does not have an electronic bias. [Pg.844]

Several studies have been performed to investigate the compatibalizing effect of blockcopolymers [67,158, 188,196-200], It is generally shown that the diblock copolymer concentration is enhanced at the interface between incompatible components when suitable materials are chosen. Micell formation and extremely slow kinetics make these studies difficult and specific non-equilibrium starting situations are sometimes used. Diblock copolymers are tethered to the interface and this aspect is reviewed in another article in this book [14]. [Pg.391]

Syntheses in which a reaction of a mononuclear metal complex precursor gives a tethered metal cluster are rare an early example is the formation of a tetrairidium carbonyl on a phosphine-fimctionaUzed polymer [17]. [Pg.216]

Vinyl cyclopropanes tethered to an aUcyne chain 127 were also subjected to the cycloisomerisation reaction in presence of the NHC-Ni catalyst system (Scheme 5.34) [39], The product formation depends on the substrate used and the NHC hgand. When SIPr carbene is used, three different products were obtained depending on the size of the R group attached to the alkyne moiety. If R is small (like a methyl) product 128 is obtained exclusively. If R is Et or Pr a mixture of 128 and 129 is obtained in 3 2 to 1 2 ratio, respectively. However, when R is large groups such as Bu or TMS only product 130 is obtained. When IfBu carbene 131 is used as the ligand, cycloisomerisation of 127 afforded product 128 exclusively, regardless of substituent size (Scheme 5.34) [39]. [Pg.149]

The properties and yield of the polymer product were correlated to the NHC identity, providing clear evidence that the NHC ligand was bound and influenced the reaction. Smaller R groups (Me, Et) on 39-R provided low molecular weights, yields, and detectable amounts of impurity. Sugiyama only examined the influence of sterics on the formation of PC, but the initial success inspired Tanaka and coworkers to extend this application by tethering NHC ligands to styrene beads [48]. [Pg.229]

A possible reaction mechanism shown in Scheme 7-10 includes (a) oxidative addition of the S-H bond to Pd(0), (b) insertion of the allene into the Pd-H bond to form the tt-allyl palladium 38, (c) reductive elimination of allyl sulfide, (d) oxidative addition of the I-aryl bond into the Pd(0), (e) insertion of CO into the Pd-C bond, (f) insertion of the tethered C=C into the Pd-C(O) bond, and (g) P-elimination to form 37 followed by the formation of [baseHjI and Pd(0). [Pg.228]


See other pages where Tether formation is mentioned: [Pg.158]    [Pg.158]    [Pg.121]    [Pg.291]    [Pg.292]    [Pg.343]    [Pg.373]    [Pg.385]    [Pg.386]    [Pg.386]    [Pg.387]    [Pg.235]    [Pg.20]    [Pg.158]    [Pg.158]    [Pg.121]    [Pg.291]    [Pg.292]    [Pg.343]    [Pg.373]    [Pg.385]    [Pg.386]    [Pg.386]    [Pg.387]    [Pg.235]    [Pg.20]    [Pg.64]    [Pg.34]    [Pg.150]    [Pg.168]    [Pg.398]    [Pg.461]    [Pg.155]    [Pg.651]    [Pg.133]    [Pg.325]    [Pg.228]    [Pg.305]    [Pg.3]    [Pg.352]    [Pg.278]    [Pg.237]    [Pg.610]    [Pg.27]   


SEARCH



Tether

Tethering

© 2024 chempedia.info