Disposable tethers in synthetic organic chemistry

Gauthier, Donald R.; Zandi, Kathleen S.; Shea, Kenneth J.

doi:10.1016/s0040-4020(97)10304-0

Cited by 166 publications

(64 citation statements)

References 146 publications

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“…The tethering of the dienophile to the diene moiety often facilitates Diels-Alder reactions and ensures the stereochemical outcome of the cycloaddition [56][57][58][59]. However, in our hands, linking quinone (S)-2 with allylic alcohol 16, either as a carbonate (cf.…”

Section: Other Dienes Studiedmentioning

confidence: 91%

Diels-Alder Reactions of 12-Hydroxy-9(10®20)-5aH-abeo-abieta-1(10),8(9),12(13)-triene-11,14-dione

et al. 2013

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12-Hydroxy-9(10→20)-5aH-abeo-abieta-1(10),8(9),12(13)-triene-11,14-dione (quinone 2) served as the dienophile in numerous intermolecular Diels-Alder reactions. These cycloadditions were conducted either thermally (including microwave heating) or with Lewis acid activation. While most dienes reacted with quinone 2 in good chemical yield, others were incompatible under the experimental conditions used.

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Section: Other Dienes Studiedmentioning

confidence: 91%

Diels-Alder Reactions of 12-Hydroxy-9(10®20)-5aH-abeo-abieta-1(10),8(9),12(13)-triene-11,14-dione

et al. 2013

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“…The volatile components, including excess diisopropylsilane, were removed under reduced pressure to give a quantitative yield of product 1 which was used in the next step without further purification. 1 …”

Section: Ethyl (2s)-2-[(diisopropylsilyl)oxy]propanoate (1); Typical mentioning

confidence: 99%

“…1 H NMR (CD 2 Cl 2 ): d = 7.02 (d, J = 6.4 Hz, 2 H), 6.83 (d, J = 6.4 Hz, 2 H), 4.57 (q, J = 6.7 Hz, 1 H), 4.13 (q, J = 7.2 Hz, 2 H), 2.26 (s, 3 H), 1.41 (d, J = 6.7 Hz, 3 H), 1.24 (t, J = 7.1 Hz, 3 H), 1,20-1.11 (m, 2 H), 1.08-1.5 (m, 12 H). 13 C NMR (CD 2 Cl 2 ): d = 173.…”

Section: Ethyl (2s)-2-{[diisopropyl(4-methylphenoxy)silyl]oxy}pro-panmentioning

confidence: 99%

A Mild Synthesis of Unsymmetrical Bis-Alkoxysilanes through Catalyzed Alcoholysis of Hydridosilanes

Scott¹,

Wilcox²

2004

Synthesis

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A mild method for the synthesis of unsymmetrical bisalkoxysilanes has been developed. This method utilizes two readily available catalysts (rhodium acetate dimer and 10% palladium on carbon) that, under neutral aprotic conditions and within reasonable time, give very good yields of the product in two steps without need to isolate intermediates. Equation 1The uses of silicon ethers in organic synthesis include the formation of tethered reactants for stereospecific intramolecular reactions, 1,2 protecting agents for many functional groups, 3 and anchoring reagents and substrates for solid support synthesis. 4 Silyl ethers are employed due to their compatibility with a wide range of reaction conditions and the ease with which they are removed. Silicon tethers through bis-alkoxysilanes (silyl ketals) are commonly prepared from the dichlorosilanes by reaction with an alcohol in the presence of base, and these conditions are not compatible with some base labile compounds. To make unsymmetrical bis-alkoxysilanes requires a method for breaking the symmetry of the dichlorosilane. Without such a method, one must accept a statistically determined mixture of mono-alkoxy and bis-alkoxy products. This may be acceptable for inexpensive readily available alcohols, but precludes the use of bis-alkoxysilane tethers for high-value synthetic intermediates. To overcome these limitations to bis-alkoxysilane synthesis, we investigated catalysts for the controlled alcoholysis of hydridosilanes.Catalytic alcoholysis of silanes by a variety of transition metal based catalysts is a very useful method to form silyl ethers under mild conditions. The process is atom-economical; typically hydrogen gas is the only by-product. To date this mild method has not been fully exploited in organic synthesis for the preparation of unsymmetrical bis-alkoxysilanes. A catalytic synthesis using silicon alcoholysis would circumvent the need of bases (and the attendant formation of protic byproducts), and eliminate the need for excess silicon dichlorides in the first ether formation. We sought catalytic methods that would ultimately allow formation of chiral tethers that are asymmetric at the silicon center. Herein we report an efficient method for the synthesis of unsymmetrical bis-alkoxysilanes from dihydridosilanes in two consecutive catalyzed alcoholysis reactions (Equation 1).There have been several reports of catalytic methods for alcoholysis of trialkylsilanes, 5 however only a few of these papers have discussed any reaction with dialkyl(dihydrido)silanes. 5b,e,h,f Among the more active catalysts for the preparation of trialkylsilyl ethers from silyl hydrides are Crabtree's cationic complex [IrH 2 (THF) 2 (PPh 3 ) 2 ] SbF 6 , 5d Wilkinson's catalyst Rh(PPh 3 ) 3 Cl, 5e Stryker's catalyst [PPh 3 CuH] 6 , 5f rhodium(II) perfluorobutyrate Rh 2 (pfb) 4 , 5b and Mn(CO) 5 Br and its dimer [Mn(CO) 4 Br] 2 . 5c A practical catalyst for silane alcoholysis should be compatible with a variety of functional groups, notably unsaturated functional groups which are k...

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“…The tether is also to be chosen for some steric effect, such as the tether control group effect [34][35][36] or the buttressing effect 53 , which are used to advantage to force the diene and dienophile groups into greater proximity. c) The tether is less permanent and not to be used in the cycloadduct's further chemistry, as is the case with the protecting group strategy 54 involving silyl ether tethers [55][56][57] . d) The tether is temporary to the point of being created in situ during the reaction, leading to the transition state, and being removed from the cycloadduct at the end of the reaction.…”

Section: Chains Bridges Tethers Spacers and Linkersmentioning

confidence: 99%

“…The use of less permanent tethers such as silyl ethers has become important as can be judged by three recent reviews on this subject [55][56][57] , and Scheme 20 in which two examples are shown. The preparation of organosilanes is now quite common so that their coupling through silyl ether bonds is straightforward and allows IMDA reactions to proceed smoothly.…”

Section: Scheme 12mentioning

confidence: 99%