685087-82-5Relevant academic research and scientific papers
On the mechanism of the reductive metallation of asymmetrically substituted silyl chlorides
Oestreich, Martin,Auer, Gertrud,Keller, Manfred
, p. 184 - 195 (2007/10/03)
An investigation of the stereochemical course of the reductive metallation of silyl chlorides with silicon-centred chirality has revealed two major events which are detrimental to stereoselection during silyl anion formation: (1) chloride-induced racemisation of silyl chlorides and (2) nonstereoselective formal dimerisation during metallation providing the corresponding disilane. In control experiments, the stereochemical course of these processes has been independently verified for the reductive metallation of the enantioenriched cyclic silyl chloride (SiS)-7a (R = H, er ≥ 88:12). A screening of several related derivatives of (SiS)-7a led to the sterically encumbered silyl chloride (SiR)-7c (R = iPr, er ≥ 94:6) which displays some unique features. This structural modification prevents racemisation by lithium chloride (T -40 °C) as well as dimerisation (T -100 °C) thus allowing for the first generation of an asymmetrically substituted silyl anion (SiS)-8c (er = 74:26) by reductive metallation of a silyl chloride with silicon-centred chirality. Moreover, the enantiospecificity of the preparation of (SiA)-7c by chlorination [(SiS)-9c → (SiR)-7c] and its reduction with aluminium hydrides [(SiR)-7c → (SiR)-9c] have been unambiguously determined by X-ray crystallography as retention (≥99%) and inversion (≥99%), respectively. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).
A Convergent Method for the Synthesis of Highly Enantiomerically Enriched Cyclic Silanes with Silicon-Centered Chirality
Oestreich, Martin,Schmid, Ulrike K.,Auer, Gertrud,Keller, Manfred
, p. 2725 - 2739 (2007/10/03)
A preparatively straightforward methodology has been developed which allows the assembly of silicon-containing carbocycles as mixtures of diastereomers with silicon as the sole center of stereogenic information. One-step construction of the chiral cyclic silanes is realized by reaction of equimolar amounts of a dibromide and a chirally modified dichlorosilane under Barbier conditions giving access to several monofunctionalized 1-sila-1,2,3,4-tetrahydronaphthalenes and a corresponding phenanthrene derivative. Facile large scale syntheses of 3-(2-bromoaryl)propyl bromides as well as dichlorosilanes have been elaborated. This highly convergent methodology relies on the novel (-)-menthyloxy-substituted dichlorosilanes, which have the chiral auxiliary for the subsequent optical resolution installed. These enantiopure dichlorosilanes are useful building blocks for a general and modular one-step approach to silanes with silicon-centered chirality since this strategy avoids the linear sequences reported in literature. The optical resolution has been exemplarily optimized for the 1-phenyl-1-sila-1,2,3,4- tetrahydronaphthalene derivative and the absolute configuration has been established by X-ray crystallography. The chiral auxiliary is stereospecifically displaced by simple reduction providing the highly enantioenriched silane (er = 98:2) which is enantiospecifically chlorinated as verified by a Walden inversion at silicon.
