Temporary silicon-tethered

For the synthesis of C2-symmetric 1,4-diol, Evans planned temporary silicon-tethered ring-closing metathesis, and asymmetric synthesis of D-altritol was... 

Intramolecular anodic olefin coupling reactions involving allyl- (equation 18) and vinyl-silanes (equation 19) can lead to good yields of quaternary carbons with control of the relative stereochemistry19,20. This is the first example of an electrochemical reaction that makes use of a temporary silicon tether. 

A diastereoselective formal addition of a 7ra i-2-(phenylthio)vmyl moiety to a-hydroxyhydrazones through a radical pathway is shown in Scheme 2.29. To overcome the lack of a viable intermolecular vinyl radical addition to C=N double bonds, not to mention a reaction proceeding with stereocontrol, this procedure employs a temporary silicon tether, which is used to hold the alkyne unit in place so that the vinyl radical addition could proceed intramolecularly. Thus, intermolecular addition of PhS" to the alkyne moiety in the chiral alkyne 161 leads to vinyl radical 163, which cyclizes in a 5-exo fashion, according to the Beckwith-Houk predictions, to give aminyl radical 164 with an a 7z-arrangement between the ether and the amino group. Radical reduction and removal of the silicon tether without prior isolation of the end product of the radical cyclization cascade, 165, yields the a-amino alcohol 162. This strategy, which could also be applied to the diastereoselective synthesis of polyhydroxylated amines (not shown), can be considered as synthetic equivalent of an acetaldehyde Mannich reaction with acyclic stereocontrol. 

Analogously, intramolecular hydrosilation reactions have been carried out with alkenes cyclization of alkenyloxy-silanes catalyzed by thiols <1998J(P1)467> and by Pt <1996TL827> has been described. In addition, intramolecular temporary silicon-tethered rhodium-catalyzed [4- -2- -2]-cycloisomerization reactions have been carried out by Evans and Bawn (Equation 50) <2004JA11150>. 

An efficient synthesis of adenophostin (55a) analogues (55b-f) from d-xylose has been reported." The C-glycosidic analogue of adenophostin A and its uracil congener (56a,b) have also been prepared via a temporary silicon-tethered radical coupling reaction as the key step. ... 

Scheme 12. Stereospecific synthesis of C-styryl glycosides using temporary silicon tethering...

Tebbe olefination, 441 Tebbe olefinations, 368 Tebbe s reagent, 457 Tedania ignis, 246 Tedanolide, 246 tedanolide, 256 TEMPO, 250, 301 temporary silicon tether, 103 Tennant quinoline synthesis, 7 tetra-n-butylammonium fluoride (TBAF), 214 2-(7-aza-1 H-benzotriazole-1 -yl)-1,1,3, 3-tetramethyluronium hexafluorophosphate (HATU), 25... 

Methodology and natural product synthesis by temporary silicon-tethered ring-closing metathesis 12CEJ5800. 

Silicon-tethered Ene Reactions. Silicon-tethered cyclization reactions have been widely utilized because of the ease of formation and removal of the temporary silicon tether and the ability of organosilicon compounds to tolerate many commonly used organic transformations. One example involves the ene reaction of a-(prenyl)dialkylsilyloxy aldehydes (eq 13). A 1,2-diol (39) can... 

Vinyl siloxonium ion 14 also serves as an important intermediate en route to conjugate adducts of unsaturated carbonyl compounds. For example, treatment of cyclohexenone (13) with reactive silyl electrophiles affords y-functionalized silyl enol ethers 15 and 16 suitable for subsequent synthetic transformations (eq 4). The temporary silicon tether (TST) strategy has been updated (2010) by an excellent review focusing upon metal-mediated reactions. The inception of this strategy is attributable to Nishiyama and Itoh who reported the radical cycUzation of acyclic bromomethyl silyl ethers to sUoxanes and their subsequent oxidation to 1,3-diols. Shortly thereafter, the group of Gilbert... 

The TST strategy has been the subject of diverse applications. For example, the Shea research group employed the concept of type II intramolecular Diels-Alder chemistry in conjunction with a temporary silicon tether and a chiral 1,2-diol auxiliary to effect diastereomeric transformation of 28 to compounds 29 and 30 in a 1 6 ratio (eq 8). ... 

These selectivity issues were solved with the intramolecular version using temporary silicon-tethered partners of the cycloaddition [52],... 

Evans, P A., Baum, E. W. (2004). Diastereoselective intramolecular temporary silicon-tethered rhodium-catalyzed [4+4+2] cycloisomerization reactions regiospecific incorporation of substituted 1,3-butadienes. Journal of the American Chemical Society, 126, 11150-11151. 

It was beneficial to employ this temporary silicon tether motif not only because of the ease of its deprotection but also because it provided easy access to deuter-ated biaryls and biphenols (Scheme 4.38). 

With the above points in mind, Sinay s group developed a direet approach to C-linked disaccharides employing a temporary silicon tether approach to graft the... 

Temporary Silicon-tethered RCM (TST-RCM) of Enyne and Dienyne Temporary silicon-tethered strategies of enyne and dienyne metathesis have been studied to demonstrate the stereoselective formation of acyclic tri- and tet-rasubstituted 1,3-dienes to circumvent the problems with controlling chemo-, regio-, and stereoselectivity in the CM... 

Evans PA, Cui J, Buffone GP. Diastereoselective temporary silicon-tethered ring-closing-metathesis reactions with prochiral alcohols a new approach to long-range asymmetric induction. Angew. Ghem. Int. Ed. 2003 42 1734-1737. 

Temporary Silicon-Tethered Ring-Closing Metathesis Reactions in Natural Product Synthesis... 

Temporary Silicon—Tethered Ring—Closing Metathesis Reactions I 233... 

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