The temporary silicon connection method in the control of regio- and stereochemistry. Applications to radical-mediated reactions. The stereospecific synthesis of C-glycosides

Abstract

Electron-transfer (ET) theory describes rates in terms of nuclear-reorganization ( ) and electronic-coupling (//AB) parameters.1 These parameters are most directly determined from the driving-force dependence of the ET rate (ideally at high driving forces in the neighborhood of X).2 Remarkably slow ET rates have been observed at low driving forces (-(7°< 0.3 eV) in certain iron-sulfur3 and blue copper proteins,4 and at high driving forces in Ru(bpy)2L(His-33) (bpy = 2,2'-bipyridine; L = imidazole, pyridine, H20; His = histidine) derivatives of cytochrome c (cyt c).5 Since the latter results conflict sharply with the much faster ET rates reported for Ru-modified Zn-substituted cytochrome c (Ru-Zn-cyt c)2,6 and Ru(bpy)2(dcbpy)-labeled ferrocytochrome c (dcbpy = dicarboxybipyridine),7,8 we have determined the Ru(bpy)2L(His-33)-cyt c kinetics by using a novel flash-quench method that allows the observation of rates over an extremely wide range.9"11The rate of intramolecular oxidation of horse heart ferrocytochrome c by Ru(bpy)2(im)(His-33)3+ (im = imidazole) 12,13

Samarium Diiodide Mediated Reactions in Total Synthesis

“…Beau, Skrydstrup, and co-workers reported the use of SmI 2 as an alternative to the more commonly employed tin hydrides in the construction of C-glycosides. [18] Following a modification of a procedure developed by Stork et al, [19] a temporary silicon group was used to tether the two glycoside units, as shown in 21 (Scheme 7). Through the course of this project, it was discovered that the use of a 2-pyridinyl sulfone group, instead of the more commonly employed phenyl sulfone moiety, eliminated the need for HMPA.…”

Samariumdiiodid‐vermittelte Reaktionen in der Totalsynthese

“…Nach einer von Stork et al. entwickelten,19 modifizierten Methode wurden die beiden Glycosideinheiten wie in 21 über eine temporäre Siliciumgruppe verknüpft (Schema ). Im Verlauf dieser Arbeit stellte sich heraus, dass bei Verwendung einer 2‐Pyridinylsulfonylgruppe anstelle des gebräuchlicheren Phenylsulfonylrests keine Zugabe von HMPA erforderlich ist.…”

Photoresponsive Supramolecular Systems: Self‐Assembly of Azodibenzoic Acid Linear Tapes and Cyclic Tetramers

“…Total synthesis : A number of C‐glycosides of Scheme , and have been reported in the past, although the polyhydroxy chain was not differentiated. Stereoisomer meso ‐ 3 16–19 (derived from D ‐glucose), D ‐ D hybrid 8 18–20 (from meso‐ 3 by L → D change), 5 ,17, 19 ent‐ 5 19, 21 and ent‐ 6 19 have been accessible. In each case a carbohydrate from the chiral pool was modified to provide the desired target.…”