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DOI: 10.1055/s-2003-42477
A Convergent Method for the Synthesis of Highly Enantiomerically Enriched Cyclic Silanes with Silicon-Centered Chirality
Publication History
Publication Date:
21 November 2003 (online)

Abstract
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 (-)-menthyl-oxy-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.
Key words
Grignard reactions - cyclizations - enantiomeric resolution - heterocycles - silicon
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References
To whom inquiries about the reported crystal structure analyses should be addressed.
16So far very few enantiomerically enriched cyclic silanes have been reported [7] [17] with only 2 (Figure [1] ) being accessible in reasonable amounts; however the benzylic position has been shown to be a reactive site. [18]
35The major shortcoming of preparative reversed phase flash chromatography is the exeptionally costly reversed phase silica gel, which we found to be long-lasting with respect to the number of chromatographies and the quality of the product separation. MeCN was simply distilled at a rotary evaporator in a fume cupboard and re-used.
37Since (SiR)-25b is a light liquid wherefore the 1-sila-1,2,3,4-tetrahydronaphthalenes 25 needed to be structurally characterized with the (SiRS)-25c instead which is isolated as a highly viscous oil which solidified upon standing.
38Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-208732(23a), CCDC-208733 [(SiRS)-25c], and CCDC-208734 [(SiS)-22b]. Copies of the data can be obtained free of charge on application to CCDC 12 Union Road Cambridge CB21EZ UK [fax: +44(1223)336033; email: deposit@ccdc.cam.ac.uk].