DBU-Promoted Facile, Chemoselective Cleavage of Acetylenic TMS Group

Abstract

Acetylenic trimethylsilyl (TMS) groups were efficiently removed using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). With either 1.0 or even 0.1 equivalents of DBU, smooth desilylation of various terminal acetylenic TMS groups was accomplished selectively in the presence of alkyl silyl ethers and other base-labile groups. Furthermore, more sterically hindered terminal acetylenic silyl groups such as TBDMS and TIPS remained intact under these conditions.

Key words

DBU - silylacetylene - chemoselective - deprotection

References and Notes

• 1a Greene TW. Wuts PGM. Protective Groups in Organic Synthesis   4th ed.:  Wiley and Sons; New York: 2000. 
• 1b Kocienski PJ. Protecting Groups   Thieme; New York: 1994. 
• For review, see:
• 2a Lalonde M. Chan TH. Synthesis  1985,  817 
• 2b Crouch RD. Tetrahedron  2004,  60:  5833 
• 3a Yeom C.-E. Kim HW. Lee SY. Kim BM. Synlett  2007,  146 
• 3b Yeom C.-E. Kim YJ. Lee SY. Shin YJ. Kim BM. Tetrahedron  2005,  61:  12227 
• 4a Bohlmann F. Burkhart FT. Zero C. Naturally Occurring Acetylenes   Academic Press; London, New York: 1973. 
• 4b Bringmann G. Walter R. Weirich R. Angew. Chem., Int. Ed. Engl.  1990,  29:  977 
• 4c Caroll RL. Forman CB. Angew. Chem. Int. Ed.  2002,  41:  4378 
• 4d Zhao D. Moore JS. J. Org. Chem.  2002,  67:  3548 
• 4e Dillinger S. Bertus P. Pale P. Org. Lett.  2001,  3:  1661 
• 5a Nielson MB. Diederich F. Synlett  2002,  544 
• 5b Alzeer J. Vasella A. Helv. Chim. Acta  1996,  78:  1219 
• 5c Kusaka S.-I. Dohi S. Doi T. Takahashi T. Tetrahedron Lett.  2003,  44:  8857 
• 5d Meert C. Wang J. De Clerq PJ. Tetrahedron Lett.  1997,  38:  2179 
• 5e Fiandanese V. Bottalico D. Marchese G. Tetrahedron  2001,  57:  10213 
• 6 Orsini A. Vitérisi A. Bodlenner A. Weibel J. Pale P. Tetrahedron Lett.  2005,  46:  2259 
• 7 Yeom C.-E. Kim MJ. Kim BM. Tetrahedron  2007,  63:  904 

8

A Representative Procedure the Desilylation of Acetylenic TMS
To a magnetically stirred solution of 1 (195 mg, 0.563 mmol) in MeCN (1.1 mL) and H₂O (56 µL) were added DBU (84 µL, 0.563 mmol) at r.t. The mixture was heated to 60 °C, and the stirring was continued for 40 min. After completion of the reaction, the resulting residue was concentrated under reduced pressure and purified by passing through a short silica gel column (ca. 5 cm) to afford pure alkyne (155 mg, 99% yield).

9

Determined from GC analysis using HP-5 column (crosslinked 5% PH ME polysiloxane).