Trimethylsilyl chloride-mediated

A parallel solid-phase synthesis of l,3,4-thiadiazolium-2-aminides involves trimethylsilyl chloride mediated cyclization of resin bound aldehydes 269 and 1,4,-disubstituted thiosemi-carbazides 268 <04JCO746>. Two additional combinatorial approaches have been developed to prepare focused libraries of 1,3,4-thiadiazoles <0478627 04BBR1053>. 1,3,4-Thiadiazoles 273 are prepared by condensation of triazole 271 with various carboxylic acids 272 in the presence of phosphorus oxychloride <04IJHC69>. 

Trimethylsilyl chloride-mediated Biginelli reaction of S-ethyl acetoace-tate 218 (Z = O X = O, S), aromatic aldehydes and urea furnish 219 (Z = O ... 

Intramolecular acylation of alkylsilanes. Cyclopentanones can be prepared by ring closure of 5-(trimethylsilyl)alkanoyl chlorides mediated by AlCl,. The starting materials are readily available from alkylation of the dianion of a carboxylic acid with a 3-(trimethylsilyl)alkyl bromide or iodide (equation 1). 

A new microwave-assisted protocol for the generation of diversely substituted 3,4-dihydropyrimidine-5-carboxylic acid esters 40 has been developed by Kappe and co-workers [88, 89] using trimethylsilyl chloride (TMSCl) as a mediator for the Biginelli MCR. This involved the reaction of S-ethyl acetothioacetate or ethyl acetoacetate, an aromatic aldehyde and (monosubstituted) urea or thiourea as building blocks. Also sterically hindered aromatic and heterocyclic aldehydes... 

Bismuthinate-mediated A -acylation of amides with carboxylic acids 321 Chlorination of alcohols with trimethylsilyl chloride in the presence of a catalytic amount of BiCla 430... 

A multistep conversion of 2,2-disubstituted 1,3-cyclohexadiones 191 to 3-substi-tuted 2-cyclohexenones 192 mediated by phosphonate anions was applied by Yamamoto and Furuta [69] in a formal synthesis of ( )-a-acoradiene (193) (Scheme 47). 3-Substituted 2-cyclohexenones are versatile building blocks for the synthesis of cyclic natural products such as spirocyclic and fused ring sesquiterpenes. These cyclohexenones were easily obtained in a one-pot reaction of 194 with dimethyl methanephosphonate anion in the presence of trimethylsilyl chloride. The new overall reaction is a multistep rearrangement involving... 

Valence tautomerization of pyrimidine-alkyne photoadducts is mediated by treatment with trimethylsilyl chloride/hexamethyldisilazane, followed by silica gel, affording diazocin-2,4-dione derivatives (8) in good yield (vide supra) <82TL4207,83JOC2337). Oxidative cleavage of a bicyclic diaza compound by rose Bengal-sensitized addition of oxygen affords the benzo-3,4-dihydro-1,3-diazocin-2,6(17/,5//)-dione derivative (38) (Equation (15)) <87H(26)2477>. 

TMSOTf also plays an important role in sugar chemistry. In fact it often mediates in the formation of the glycosidic bond, either alone or in conjunction with trimethylsilyl chloride, Af-bromosuccinimide (NBS), or iV-iodosuccinimide (NIS). In such reactions, different moieties have acted as leaving groups in the glycosyl donor and 0-, N-, or C-nucleophiles have been employed (eq 86). The addition of hydroxyl unprotected sugar units to the ero-anomeric double bond of ketene dithioacetals, which act as glycosyl donors, is also promoted by TMSOTf. 6... 

Cyclization of 2-but-3-enylcyclohexanes mediated by zinc in the presence of trimethylsilyl chloride may also be influenced by the same controlling factors. Corey reported [12] that c -2-but-3-enyl-4-f-butylcyclohexane gave mostly an enrfo-methyl-cw-hydrindanol. The 1,5-cis/trans ratio was reported to be 66 7. 

An intramolecular nucleophilic displacement, followed by chloride-mediated desilylation, leads to the formation of a bis(trimethylsilyl)-S2N2 ring ... 

Dieter and coworkers reported an enantioselective total synthesis of (R)-pyrrolam (48), which involved an intramolecular cyclization of a y-aminoester as a key step (2002JOC847,2004JOC6105 Scheme 8). Enantioselective metaUation of a Boc-pyrrolidine (78) mediated by (—)-sparteine, followed by transmetaUation to the cuprate, and cross-coupling with (Z)-3-iodopropenoate (79) gives the corresponding y-aminoester (80). The best conditions for the subsequent deprotection/cyclization to (R)-pyr-rolam (48) involve trimethylsilyl chloride and phenol. 

Mukaiyama aldol reactions of aldehydes with silyl enol ethers are amongst the most widely used Lewis-acid-mediated or -catalyzed reactions. However, trimethylsilyl triflate is not active enough to promote these reactions,66 and more active silicon-based Lewis acids have been developed. One example is the species generated by mixing trimethylsilyl triflate (or chloride) and B(OTf)3,319,320 for which the formulation R3Si + [B(OTf)4] is suggested by NMR experiments. Only a catalytic amount of this was needed to complete Mukaiyama aldol reactions of... 

A useful application of the silver-mediated additions is 1,3 -diene synthesis by three-carbon elongation of aldehydes [48,51,53]. The bimetallic reagent 3-trimethylsilyl-l-propenylzirco-nocene chloride (A Scheme 8.23) reacts with aldehydes under the influence of a catalytic amount of Ag+ to give the intermediate zirconocene-alkoxide B, which then undergoes a Peterson-type 1,4-elimination of TMS alkoxide to stereoselectively afford ( )-dienes (fc/Z > 96 4) (Scheme 8.23). A Wittig reaction yields the same products without stereoselectivity (ca. 1 1 mixtures of E- and Z-isomers). 

The synthesis of terminal alkenes entails addition of either (trimethylsilyl)methyl-magnesium chloride (Me3SiCH2MgCl) or (trimethylsilyl)methyllithium (Me3SiCH2Li) to an aldehyde or a ketone to yield the corresponding P-hydroxysilane, which undergoes base- or acid-mediated elimination to furnish the alkene, as exemplified below. " ... 

Although it was stated that allyltrialkylsilanes were unsuccessful in the Lewis acid mediated addition to acryloylFp complexes, a stereoselective procedure has been developed for [3 + 2] cycloadditions of allylsilanes to enones10. The reaction occurs in the presence of titanium(IV) chloride (TiCl4) as Lewis acid and the single cycloaddition product formed is the m-fused eyclopentane with the trimethylsilyl group in the endo orientation. The reaction appears to follow a similar pathway to the previous process although, as yet, yields and experimental procedures have not been documented. 

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