205994-56-5Relevant academic research and scientific papers
Unsuccessful attempts to add alcohols to transient 2-amino-2-siloxy- silenes-leading to a new benign route for base-free alcohol protection
Guliashvili, Tamaz,Tibbelin, Julius,Ryu, Jiyeon,Ottosson, Henrik
supporting information; experimental part, p. 9379 - 9385 (2011/01/07)
Thermolytic formation of transient 1,1-bis(trimethylsilyl)-2-dimethylamino- 2-trimethylsiloxysilene (2) from N,N-dimethyl(tris(trimethylsilyl)silyl) methaneamide (1) in presence of a series of alcohols was investigated. The products are, however, not the expected alcohol-silene addition adducts but silylethers formed in nearly quantitative yields. Thermolysis of 1 in the presence of both alcohols (MeOH or iPrOH) and 1,3-dienes (1,3-butadiene or 2,3-dimethyl-1,3-butadiene) gives alkyl-tris(trimethylsilyl)silylethers and the [4+2] cycloadducts between the silene and diene, which confirms the presence of 2 and that it is unreactive towards alcohols. The observed silylethers are substitution adducts where the amide group of the silylamide is replaced by an alkoxy group, and the reaction time is reflected in the steric bulk of the alcohol. Indeed, the formation of silylethers from the reaction of alcohols with silylamide represents a new base-free method for protection of alcohols. The protection reactions using 1 progresses at elevated temperatures, or alternatively, under acid catalysis at ambient temperature, and similar protections can be carried out with N-cyclohexyl(triphenylsilyl)methaneamide and N,N-dimethyl(trimethylsilyl)methaneamide. The latter silylamide can be used under neutral conditions at room temperature. The only by-products are formamides (N,N-dimethylformamide (DMF) or N-cyclohexylformamide), and the reactions can be performed without solvent. In addition to alcohols we also examined the method for protection of diols, thiols and carboxylic acids, and also these reactions proceeded in high yields and with good selectivities. The Royal Society of Chemistry.
Alkoxyallylsilanes: Functional protecting groups
Balduzzi, Sonya,Brook, Michael A.
, p. 1617 - 1622 (2007/10/03)
Allyl-t-butylmethylsilyl groups were shown to function as alcohol protecting groups whose hydrolytic stability was greater than t- butyldimethylsilyl (TBS) and Si(SiMe3)3 (sisyl) groups. Pseudo-first-order rate constants for the acid
The photolytic and hydrolytic lability of sisyl (Si(SiMe3)3) ethers, an alcohol protecting group
Brook,Balduzzi,Mohamed,Gottardo
, p. 10027 - 10040 (2007/10/03)
The tris(trimethylsilyl)silyl (sisyl) group is a photolabile protecting group for primary and secondary alcohols. Sisyl (tris(trimethylsilyl)silyl) ethers 2b-11b of a number of primary and secondary alcohols 2a-11a were prepared in yields ranging from 70-97%. The resulting silyl ethers were stable to aqueous bases, Grignard reagents and Wittig reagents as would be expected for bulky alkoxysilanes. They were also stable to selected fluoride salts including CsF. The sisyl ethers could be cleaved using photolysis at 254 nm in under 30 minutes to give the starting alcohols in yields ranging from 62-95%. The photolytic behaviour of sisyl ethers was examined in more detail using 2,3-dimethyl-1,3-butadiene as a silylene trap. The regiochemistry of the oligosilane fragmentation to silylenes was shown to be dependent upon the alkoxy group. The hydrolytic stability of three was compared with the analogous t-butyldimethylsilyl ethers. The relative stability of the two silyl groups can be altered by choice of solvent: in acetic acid/water the ease of hydrolysis followed the order ROSi(SiMe3)3 > ROSiMe2t-Bu; the inverse order was observed in CDCl3 using p-TsOH·H2O. Pseudo-first-order rate constants for the acidic hydrolysis of primary, benzylic, and secondary sisyl ether in AcOH/THF/H2O were determined to be 3.74 x 10-2 s-1, 1.94 x 10-2 s-1, and 1.30 x 10-2 s-1, respectively. The analogous rate constants for the TBS ethers were determined to be 6.04 x 10-3 s-1, 3.53 x 10-3 s-1, and 3.49 x 10-3 s-1, respectively.
