Silyl protecting groups
From Wikipedia, the free encyclopedia
In organic chemistry, various triorganosilyl compounds are used as protecting groups. The simplest is the trimethylsilyl group, but others are known.
In an NMR spectrum, signals from atoms in trimethylsilyl groups in compounds will commonly have chemical shifts close to the tetramethylsilane reference peak at 0 ppm. Also compounds, such as high temperature silicone "stopcock" grease, which have polysiloxanes (often called silicones) in them will commonly show peaks from their methyl groups (attached to the silicon atoms) having NMR chemical shifts close to the tetramethylsilane standard peak, such as at 0.07 ppm in CDCl3.[1]
Super silyl groups
silyl.svg)
Related to trimethylsilyl groups are "super" silyl groups of which there exist two varieties: A silicon group connected to three trimethylsilyl groups makes a tri(trimethylsilyl)silyl group (TTMSS or TMS3Si) and a silicon group connected to three tert-butyl groups. The TTMSS group was proposed in 1993 by Hans Bock. With a van der Waals volume of up to 7 cubic angstrom it surpasses the related TIPS group (around 2)[2][3] and one potential application is its use as a temporary substituent promoting asymmetric induction for example in this diastereoselective one-pot reaction involving two sequential Mukaiyama aldol reactions:[4]
TTMSS can also stand for tris(trimethylsilyl)silane,[5][6] which is comparable as a chemical reagent to tributyltin hydride without the associated toxicity concern of organotin and tributyltin compounds.[7][8] The reagent is employed in radical reductions, hydrosilylation and consecutive radical reactions.[9]
Bibliography
- ↑ Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. J. Org. Chem. 1997, 62(21), pp 7512-7515. doi:10.1021/jo971176v
- ↑ "Super Silyl" Group for Diastereoselective Sequential Reactions: Access to Complex Chiral Architecture in One Pot Matthew B. Boxer and Hisashi Yamamoto J. Am. Chem. Soc.; 2007; 129(10) pp 2762 - 2763; (Communication) doi:10.1021/ja0693542
- ↑ Tris(trimethylsilyl)silyl-Governed Aldehyde Cross-Aldol Cascade Reaction Boxer, M. B.; Yamamoto, H. J. Am. Chem. Soc.; (Communication); 2006; 128(1); 48-49. doi:10.1021/ja054725k
- ↑ The starting materials are acetaldehyde and benzophenone which are both converted to silyl enol ether by reaction with tris(trimethylsilyl)silane and triflic acid with evolution of hydrogen. The aldol reaction is catalyzed by bis(trifluoromethane)sulfonimide
- ↑ "Tris(trimethylsilyl)silane 97%". Sigma-Aldrich Co. LLC. Retrieved 2014-05-05.
- ↑ Chatgilialoglu, Chryssostomos; Ferreri, Carla; Landais, Yannick; Timokhin, Vitaliy I. (25 June 2018). "Thirty Years of (TMS)3SiH: A Milestone in Radical-Based Synthetic Chemistry". Chemical Reviews. 118 (14): 6516–6572. doi:10.1021/acs.chemrev.8b00109. PMID 29938502. S2CID 49413857.
- ↑ Brook, Michael A. (2000). Silicon in Organic, Organometallic, and Polymer Chemistry. New York: John Wiley & Sons, Inc. pp. 172–173.
- ↑ "Tris(trimethylsilyl)silane, TTMSS". The Organic Chemistry Portal. Retrieved 2014-05-05.
- ↑ Recent Applications of the (TMS)3SiH Radical-Based Reagent, Chryssostomos Chatgilialoglu, Jacques Lalevée Molecules 2012, 17, 527-555; doi:10.3390/molecules17010527