Utilizing silicon for the synthesis of tri- and tetrasubstituted olefins
Date
2013
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Abstract
Functionalized organosilanes serve an important role as reactive precursors for a number of synthetic transformations. Consequently there is still great use for the development of new methods that allow for facile and efficient generation of organosilicon compounds. Herein, a number of such methods are described. The stereoselective syntheses of α-silylenones using catalytic PtCl2 are reported. Via alkyne activation, α-hydroxypropargylsilanes are converted to (Z)-silylenones through a highly selective silicon migration. A trans halosilylation of alkynes is also reported. Both the PtCl2 catalyzed silyl migration the halosilylation reaction proceed through a 1,2-silicon shift onto the activated alkyne intermediate in an anti fashion relative to the activating agent. Both reactions afford excellent yields and selectivity for the product tri- and tetrasubstituted alkenes. The high yielding Pt catalyzed hydrosilylation reactions of internal alkynes are described with a focus on understanding the factors that govern the regioselectivity of the process. Electronic, steric, and functional group properties all influence the selectivity, an understanding of which allows the selective formation of trisubstituted vinylsilanes, which are synthetically useful compounds for accessing stereodefined alkenes. Finally, efforts to show the synthetic utility of tri- and tetrasubstituted vinylsilanes for the formation of C-C bonds using Hiyama coupling and halodesilylation reactions are reported. Hiyama couplings of tetraorganosilanes with and without the use of fluoride activators are thoroughly evaluated. Coupling reactions with vinylsiloxanes are also shown. Finally, stereoretentive halodesilylation reactions are explored with the product vinylhalides subsequently subjected to Suzuki cross coupling conditions affording high yields of highly substituted all-carbon alkenes with good retention of alkene geometry.
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Subject
cross-coupling
stereodefined
silicon
olefins
regioselective
alkenes