Triethylsilane and trifluoroacetic acid

Ring-substituted benzyl alcohols sometimes undergo such reduction more effectively than unsubstituted alcohols. For example, treatment of a dichloromethane solution of 2,4,6-trimethylbenzyl alcohol with trifluoroacetic acid and triphenylsilane produces a 41% isolated (89% by GLC) yield of isodurene.26 Treatment of 2-me(hyl-4,6-di-/m-buty I benzyl alcohol with a three-fold excess of triethylsilane and trifluoroacetic acid in dichloromethane at room temperature gives an 85% yield of 2-mclhyl-4,6-di-/m-butyltoluene together with 15% of 3,5-di-ferf-butyltoluene. The latter is presumably formed by loss of protonated formaldehyde from the Cl ring-protonated substrate.128 Similar treatment of 2,4,6-tri-ferf-butylbenzyl alcohol produces a 90% yield of 2,4,6-tri-tert-butyltoluene within one hour (Eq. 21).128... 

The reduction of 2-(hydroxymethyl)-l,4,6,8-tetramethylazulene to 1,2,4,6,8-pentamethylazulene occurs quantitatively upon treatment with triethylsilane and trifluoroacetic acid at 60° for 19 hours (Eq. 22).163... 

While all of the above examples have involved pyrimidinone derivatives, pyrimidines themselves can also be reduced to dihydro derivatives using triethylsilane and trifluoroacetic acid <2004TL2107>. Thus, a variety of 2-aminopyrimidines 390 were reduced to their 1,6-dihydro derivatives 391 in good yield by treatment with trifluoroacetic acid (TEA) and triethylsilane at room temperature, while 5-bromopyrimidine 392 similarly gave the dihydro derivative 393 in 81% yield under the same conditions <2004TL2107>. 

The Clemmensen reduction of condensed 4//-thiopyrans 340 (R = H, Me) with zinc and hydrochloric acid gave tetrahydro derivatives 438.373 Triethylsilane and trifluoroacetic acid was used for analogous reductions of 4//-thiopyrans 45, 47, and 409 (R = H, Me, Et, Ph) to 453.362 3,5-Dideutero derivatives of 453 were obtained in the same way in the presence of O-deuteriotrifluoroacetic acid.362... 

Dicyclohexano-4//-selenopyran (62) and its 4-substituted derivatives were converted by triethylsilane and trifluoroacetic acid to stereoisomers of tetrahydro products 439 (R = H, Ph, 2-FC6H4, PhCHj).385... 

Ketones in alcohol solutions give mixed ethers with triethylsilane and trifluoroacetic acid, presumably via the hemiketal (or ketal). Similar results were obtained with ketones and silylated alcohols. Studies of the acid-catalyzed reduction of alcohols with silanes provide strong support for the postulate that carbonium ions are intermediates. ... 

Some dihydro-Reissert analogs have been prepared in this series. Thus, catalytic hydrogenation of 93 under very mild conditions or an ionic hydrogenation of 92 using triethylsilane and trifluoroacetic acid gives 97 and 98, respectively. The dihydro analog 98 has also been prepared from... 

Reduction of an aralkyl keto group. A recent example of this transformation is the conversion of 1 into 2 in 957o yield (pure) with 2.5 equiv. of triethylsilane and trifluoroacetic acid. ... 

The 1,2,3,5-oxatriazine 2-oxide moiety of 117 survived treatment with triethylsilane and trifluoroacetic acid (TFA) while the oxazolidinone moiety was reductively cleaved (Equation 2) <2003JOC2652>. 

Ionic hydrogenation with silanes can be accomplished in the presence of an acid or Lewis acid. For example, a combinahon of triethylsilane and trifluoroacetic acid (TFA) provides a non-catalyhc method for hydrogenahon of C=C, C=0 and C=N double bonds and for hydrogenolysis of some single bonds (such as C—Br or benzylic C—OH). Alkenes can be reduced to saturated hydrocarbons, but only if the double bond is at least trisubstituted, allowing the possibility of selechve hydrogenahon in a compound containing different types of double bond. A useful... 

Reactions.—A-Alkylation of acetanilides has been achieved using a two-phase system of water and benzene with sodium hydroxide as base and triethylbenzylam-monium chloride yields are better than 80%. An efficient two-step process for the A-methylation of unsubstituted amides, lactams, and ureas has been described which involves initial formation of the corresponding methylol, by treatment with formaldehyde, followed by reduction with either triethylsilane and trifluoroacetic acid or with hydrogen over palladium in TFA. A method for the methylthiomethy-lation of both amides and lactanes has appeared. ... 

The reductive cyclization of N-(w-iodoalkyl)succinimides induced by samarium(II) iodide was disclosed by Ha et al. as a novel method for making pyrrolizidines and indoUzidines (Scheme 46). " In the apphcation of the method to the synthesis of (+)-lentiginosine (127), reaction of N-(4-iodo-butyl)tartarimide (+)-335 with samarium(II) iodide in the presence of the iron(III)—tris(dibenzoylmethane) complex as catalyst produced the unsaturated indolizidin-3-one (+)-336 in 82% yield. Reduction of the bridgehead alkene was accomplished with triethylsilane and trifluoroacetic acid via an intermediate acyliminium ion, giving (+)-337 as the sole product in 93% yield. Routine hydrolysis of the silyl ethers produced the known diol (+)-177, after which reduction of the lactam with Hthium aluminum hydride then completed this short synthesis of (+)-127. 

The ionic hydrogenation of thiophens with a mixture of triethylsilane and trifluoroacetic acid, consisting of electrophilic protonation followed by hydride addition, has been used for the synthesis of (109) from (110) and of the tetra-hydrothiophen derivative (111) from the corresponding thiophen. Also, a series of 2-(co-diethylaminoalkyl)thiophens (112) has been hydrogenated with... 

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