Reduction of Carbonyl to Methylene: Organosilane-Ga(OTf) 3 as an Efficient Reductant System
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Reduction of Carbonyl to Methylene: Organosilane-Ga(OTf)3 as an Efficient Reductant System G. K. Surya Prakash • Clement Do Thomas Mathew • George A. Olah
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Received: 15 December 2010 / Accepted: 9 January 2011 / Published online: 25 January 2011 Ó Springer Science+Business Media, LLC 2011
Abstract Direct carbonyl reduction to methylene has been achieved by mild reductant system obtained from the combination of organosilane and gallium (III) trifluoromethanesulfonate {Ga(OTf)3}, a water tolerant, recyclable, catalyst. Among a series of organosilanes studied, dimethylchlorosilane (Me2SiHCl, DMCS) showed the highest efficiency. Both aromatic and aliphatic ketones were effectively reduced to the corresponding methylene products with high functional groups tolerance, under very mild conditions in a relatively short period of time with good to excellent yields. Keywords Sustainable development Organosilanes Gallium triflate Carbonyl reduction Hydrosilylation
1 Introduction Environmentally acceptable chemical processes and products are essential elements for sustainable development [1]. The scientific community is on the lookout for new sustainable media as well as catalysts for the development of environmentally benign organic processes along with suitable modifications of many reaction methodologies. The deoxygenation of aldehydes and ketones to methyl or methylene derivatives is one of the most often studied transformations in synthetic organic chemistry [2]. The first example for the reduction of carbonyl compounds to hydrocarbons was reported by Clemmensen in 1913 using
G. K. Surya Prakash (&) C. Do T. Mathew G. A. Olah Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1661, USA e-mail: [email protected]
Zn-Hg and HCl [3, 4]. Later, Wolff and Kishner developed another method for the deoxygenation of carbonyl compound to methyl or methylene derivatives via hydrazone or semicarbazone cleavage in basic media [5–8]. Following the revolutionary investigations on reduction procedures, other methods have also been developed, such as catalytic hydrogenation [9–12], reduction using H2/Raney nickel [13, 14], reduction using LiAlH4–AlCl3 [15], NaBH4–CF3CO2H [16], Et3SiH–BF3 or Et3SiH–CF3CO2H [17–19], and reaction involving the use of triisopropylphosphite [20]. All of these methods, while offering some advantages, also suffer from disadvantages in relation to their general applicability, selectivity, reaction protocol, toxicity, reaction time and yields [21, 22]. Direct catalytic procedures are also reported but drastic reaction conditions are required (150–180 bar, 270–300 °C) [23]. On the other hand, the reduction of aryl aldehydes and ketones have been successfully performed using metal hydride reagents such as aluminum hydride [24–29], boron hydride [30–36], or hydrosilane [37–41] with a combination of stoichiometric or excess amounts of Lewis or Brønsted acids. However, only few examples are available for reactions employing catalyti
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