Technical Library

Because trialkylsilyl groups are very commonly used to protect the terminal C-H of an alkyne, pro- tiodesilylation back to the parent alkyne is an important transformation. This can be accomplished with a number of mild reaction conditions. Among these is the simple reaction of the alkynyltrimethylsilane with K2CO3/MeOH or, for more hindered silanes, TBAF/THF. Examples of these are to be found throughout this short review. The selective protiodesilylation of an alkynylTMS group in the presence of an alkynylTIPS group with K2CO3/THF/MeOH illustrates the potential for selective protection/deprotection.4

Bis(trimethylsilyl)-1,3-butadiyne was selectively relieved of one of the trimethylsilyl groups by reaction with MeLi/LiBr in diethyl ether.

Scheme 2. Example of selective desilylation of an alknylsilane

Bis(trimethylsilyl)-1,3-butadiyne was metalated with one equivalent of MeLi and reacted with acrolein and subsequently protiodesilylated to yield vinyl diynyl carbinol 1. The trans metalation with five equivalents of MeLi and reaction with acrolein gave the diol 2 in excellent yield. These key intermediates were carried forth in syntheses of (+)- and (-)-falcarinol and (+)- and (-)-3-acetoxy falcarinol.5

Scheme 3. Desilylative lithiation and reactions of bis(trimethylsilyl)-1,3-butadiyne


BIPHEP 1,1’-bis(diphenylphosphino)biphenyli-PrIIsopropylimidazole
DABCO 1,4-diazabicyclo[2.2.2]octaneMPM4-Methoxybenzyl
imidazolidinium chloride
DIPADiisopropylamineTBAFTetra-n-butylammonium fluoride
Dppe1,2-Bis(diphenylphosphino)ethane TMSITrimethyliodosilane