Synthesis of alkylsilanes
Organofluorophosphonium salts exhibit Lewis acidity derived from a low-lying σ* orbital at P opposite F. Due to the acidity, these salts for example catalyze the rapid isomerization of 1-hexene to 2-hexene and a cationic polymerization of isobutylene. In the presence of hydrosilanes and a catalytic amount of an organofluorophosphonium salt, olefins and alkynes undergo efficient hydrosilylation.
M. Pérez, L. J. Hounjet, C. B. Caputo, R. Dobrovetsky, D. W. Stephan, J. Am. Chem. Soc., 2013, 135, 18308-18310.
Using triethylborane as the initiator, phenyldimethylsilane and trichlorosilane undergo efficient radical hydrosilylation reactions with various alkenes. Adducts from the trichlorosilane reactions can be oxidised to afford alcohols in moderate yields. This two-step process leads to the anti-Markovnikov hydration of alkenes.
M. J. Palframan, A. F. Parsons, P. Johnson, Synlett, 2011, 2811-2814.
Gaseous and flammable silanes are inconvenient to use in chemical reactions. Catalytic amounts of a nickel pincer complex and NaOtBu enable the synthesis of alkyl hydrosilanes from alkenes and alkoxy hydrosilanes. The scope and mechanism of the hydrosilylation reactions are also described.
I. Buslov, S. C. Keller, X. Hu, Org. Lett., 2016, 18, 1928-1931.
Pincer iron complexes with electron-donating phosphinite-iminopyridine (PNN) ligands are efficient catalysts for the anti-Markovnikov alkene hydrosilylation of primary, secondary, and tertiary silanes. More importantly, the system tolerates reactive groups such as ketones, esters, and amides. Furthermore, the iron catalysts may provide a low-cost and environmentally benign alternative to currently employed systems for alkene hydrosilylation.
D. Peng, Y. Zhang, X. Du, L. Zhang, X. Leng, M. D. Walter, Z. Huang, J. Am. Chem. Soc., 2013, 135, 19154-19166.
A Co catalyst for anti-Markovnikov alkene hydrosilylation can be generated in situ from an air-stable precursor that is simple to synthesize from low-cost, commercially available materials. This inexpensive catalyst can be used without added solvent at low temperatures with low loadings. In addition, a mixture of Co catalysts performs a tandem catalytic alkene isomerization/hydrosilylation reaction.
C. Chen, M. B. Hecht, A. Kavara, W. W. Brennessel, B. Q. Mercado, D. J. Weix, P. L. Holland, J. Am. Chem. Soc., 2015, 137, 13244-13247.
A zinc-catalyzed nucleophilic substitution reaction of chlorosilanes with organomagnesium reagents affords a broad range of functionalized tetraorganosilanes under mild reaction conditions. The reaction can be performed on large scale.
K. Murakami, H. Yorimitsu, K. Oshima, J. Org. Chem., 2009, 74, 1415-1417.
Various siletanes have been used as substrates for the oxidation of carbon-silicon bonds upon exposure to aqueous fluoride and peroxide. These tetraalkylsilanes offer a combination of stability and reactivity with many practical benefits, including compatibility with silicon protecting groups and electron-rich aromatic rings.
J. D. Sunderhaus, H. Lam, G. B. Dudley, Org. Lett., 2003, 8, 4571-4573.
In a nucleophilic displacement of the triflate leaving group attached to terminally functionalized alkyl groups, copper catalysis is used to release the silicon nucleophile from Suginome's Si-B reagent. The functional group tolerance is excellent, the reaction even tolerates halide leaving groups.
J. Scharfbier, M. Oestreich, Synlett, 2016, 27, 1274-1276.
A simple, commercially available nickel catalyst (NiBr2ˇdiglyme) can achieve couplings of unactivated alkyl bromides with nucleophilic silicon reagents under unusually mild conditions.
C. K. Chu, Y. Liang, G. C. Fu, J. Am. Chem. Soc., 2016, 138, 6404-6407.
Allylsilylation allows to install both silyl and allyl groups onto a carbon-carbon double bond directly. Proton-exchanged montmorillonite showed excellent catalytic performances for the allylsilylation of alkenes. Isolation of the reaction intermediate on the montmorillonite surface helped to investigate the reaction mechanism.
K. Motokura, S. Matsunaga, A. Miyaji, Y. Sakamoto, T. Baba, Org. Lett., 2010, 12, 1508-1511.
A water-insoluble copper(II) acetylacetonate-chiral bipyridine complex catalyzed an asymmetric silyl conjugate addition of lipophilic substrates in water. Indeed, the reactions proceeded efficiently only in water. Water seems to play a role in constructing and stabilizing sterically confined transition states and accelerating subsequent protonation.
T. Kitanosono, L. Zhu, C. Liu, P. Xu, S. Kobayashi, J. Am. Chem. Soc., 2015, 137, 15422-15425.
The presence of a catalytic amount of copper(II) and an amine base enables a mild method for the installation of the dimethylphenylsilyl group on the β-carbon of electron-deficient olefins at rt. The transformation proceeds efficiently in water within 1.5–5 h to afford β-silylated products in good yields.
J. A. Calderone, W. L. Santos, Org. Lett., 2012, 14, 2090-2093.
An efficient copper-catalyzed carbenoid insertion reaction of α-diazo carbonyl compounds into Si-H and S-H provides a broad range of α-silylesters and α-thioesters in high yields using 5 mol% of a simple copper(I) salt as catalyst. In addition, α-diazoketones can be converted to α-silylketones in moderate yields.
H. Keipour, A. Jalba, L. Delage-Laurin, T. Ollevier, J. Org. Chem., 2017, 82, 3000-3010.
In the presence of cationic rhodium complexes, Si-B compounds function as equivalents of nucleophilic silicon, which is efficiently transferred onto acyclic as well as cyclic α,β-unsaturated carbonyl compounds. [((S)-binap)Rh(cod)]ClO4 has effected an asymmetric 1,4-addition to cyclic acceptors in high enantiomeric excess.
C. Walter, G. Auer, M. Oestreich, Angew. Chem. Int. Ed., 2006, 45, 5675-5677.
A convenient method for the synthesis of 1,1-diboronates from the corresponding N-tosylhydrazones is also applicable to 1-silyl-1-boron compounds. Derivatization and consecutive Pd-catalyzed cross-coupling reactions with 1,1-boronates were also explored, demonstrating the synthetic potential of 1,1-diboronates.
H. Li, X. Shangguan, Z. Zhang, S. Huang, Y. Zhang, J. Wang, Org. Lett., 2014, 16, 448-451.
A platinum-catalyzed intramolecular silaboration of borylsilanyl homoallyl ethers gave 1-oxa-2-silacyclopentanes in high yields. The stereoselectivity of the reactions strongly depended on the used ligands. A complementary synthesis of a pair of diastereomers of 6-methylheptane-1,3,5-triol is described.
T. Ohmura, H. Furukawa, M. Suginome, J. Am. Chem. Soc., 2006, 128, 13366-13367.
Highly efficient, stereo- and regioselective palladium-catalyzed hydro-, sila-, and stannastannations of cyclopropenes gave multisubstituted cyclopropylstannanes. The addition across the double bond proceeds from the least hindered face.
M. Rubina, M. Rubin, V. Gevorgyan, J. Am. Chem. Soc., 2002, 124, 11566-11567.