Base-Catalyzed Dehydrogenative Si-O Coupling of Dihydrosilanes: Silylene Protection of Diols

Abstract

The direct dehydrogenative coupling of 1,3- and 1,4-diols and dihydrosilanes is efficiently catalyzed by Cs₂CO₃ (10 mol%), cleanly affording six- and seven-membered 1,3-dioxo-2-silacycles with dihydrogen as the sole by-product. Conversely, 1,2-diols do not yield the expected 1,3-dioxo-2-silacyclopentanes, essentially forming cyclic disiloxanes instead. Aside from the synthetic convenience, the procedure itself is also useful for straight-forward diol derivatization prior to GLC analysis.

Key words

coupling - dehydrogenation - diols - protecting groups - silicon

References and Notes

• 1a Wuts PGM. Greene TW. GreeneŽs Protective Groups in Organic Synthesis   4th ed.:  Wiley; New York: 2007.  p.299 
• 1b Kocieński PJ. Protecting Groups   3rd ed.:  Thieme; Stuttgart: 2004.  p.119 
• 2 Cragg RH. Lane RD. J. Organomet. Chem.  1984,  267:  1 
• 3 Trost BM. Caldwell CG. Tetrahedron Lett.  1981,  22:  4999 
• 4 Corey EJ. Hopkins PB. Tetrahedron Lett.  1982,  23:  4871 
• 5 Mai K. Patil G. J. Org. Chem.  1986,  51:  3545 
• 6a For late-transition-metal catalysis, see: Corey JY. In Advances in Silicon Chemistry   Vol. 1:  Larson G. JAI Press; Greenwich: 1991.  p.327 
• 6b For Brønsted and Lewis acid/base catalysis, see: Lukevics E. Dzintara M.
  J. Organomet. Chem.  1985,  295:  265 
• 7 Nakano T. Nagai Y. Chem. Express  1990,  5:  21 
• 8 Bedard TC. Corey JY. J. Organomet. Chem.  1992,  428:  315 
• 9 Lorenz C. Schubert U. Chem. Ber.  1995,  128:  1267 
• 10 Blackwell JM. Foster KL. Beck VH. Piers WE.
  J. Org. Chem.  1999,  64:  4887 
• 11 Weickgenannt A. Oestreich M. Chem. Asian J.  2009,  4:  406 
• 12 Weickgenannt A. Mewald M. Muesmann TWT. Oestreich M. Angew. Chem. Int. Ed.  2010,  49:  2223 ; Angew. Chem. 2010, 122, 2269
• 13 van Look G. Simchen G. Heberle J. Silylating Agents   Fluka Chemie AG; Buchs: 1995.  p.111 
• 15 Cragg RH. Lane RD. J. Organomet. Chem.  1985,  289:  23 
• 17a Silcox CM. Zuckerman JJ. J. Organomet. Chem.  1966,  5:  483 
• 17b Yang M.-H. Yeh F.-J. J. Chin. Chem. Soc.  1991,  38:  57 

14

General Procedure for Silylene Protection A flame-dried Schlenk flask was charged with Cs₂CO₃ (10 mol%). The flask was evacuated and backfilled with argon prior to the successive addition of the diol (1.0 equiv) dissolved in THF (0.15 M) and the dihydrosilane (1.2 equiv) dissolved in THF (0.50 M). The reaction mixture was maintained at r.t. for the indicated time, and the base was then filtered off. The filtrate was evaporated under reduced pressure, affording the crude silylene-protected diols, which were purified by flash column chromatography on silica gel.

16

The reaction of Ph₂SiH₂ with H₂O in the absence of base yields disiloxane (Ph₂HSi)₂O (cf. ref. 8).