Simultaneous accumulation and derivatization of volatiles using the dynamic solvent effect

A method for the derivatization of volatiles collected using the dynamic solvent effect (DSE) is described. Trimethylsily ethers and esters (using N,O-bis-trimethylsilyltrifluoracetamide) are produced on the porous bed of a DSE concentrator either during or after collection of airborne volatiles. Peak areas obtained in the gas chromatographic analysis of test compounds gave coefficients of variation of less than 10% for amounts considerably less than 100 ng. Little, if any, adsorption or other loss of compounds occurs. The analysis of the volatiles collected from an individual queen of the honeybee, Apis mellifera scutellata, is presented to illustrate the utility of the technique.     

Reaction of aryl azides with tris(trimethylsilyl)silyllithium: Synthesis of tmeda or thf adducts of [Li{N(Ar)Si(SiMe3)3}] and 1,4-trimethylsilyl migration from oxygen to nitrogen

Reaction of ArN₃ (Ar = Ph, p-MeC₆H₄, 1-naphthyl) with [Li{Si(SiMe₃)₃}(thf)₃] yielded lithium amides [Li{N(Ar)Si(SiMe₃)₃}L] (L = tmeda or (thf)₂). Similar treatment of o-phenylene diazide with 2 equiv. of [Li{Si(SiMe₃)₃}(thf)₃] formed dilithium diamide complex 4. Reaction between o-Me₃SiOC₆H₄N₃ and [Li{Si(SiMe₃)₃}(thf)₃] afforded, via 1,4-trimethylsilyl migration from oxygen to nitrogen, [Li{OC₆H₄{N(SiMe₃)Si(SiMe₃)₃}-2}]₂ (5). The structures of complexes 3 and 5 have been determined by single crystal X-ray diffraction techniques.     

Two-carbon homologation of ketones via sily ketene acetals: Synthesis of α,β-unsaturated acids and α-trimethylsilyl δ-ketoacids

The reaction of C,O,O-tris(trimethylsilyl)ketene acetal 1 with saturated, cyclic and aromatic ketones 2 proceeds smoothly in the presence of titanium chloride to give (E)-α,β-unsaturated carboxylic acids 3 with fairly good stereoselectivity. With α,β-unsaturated ketones 4, α-trimethylsilyl δ-ketoacids 5 (syn + anti) are obtained according to Michael-type 1,4 addition. These diastereoisomers are separated and the configurations of 5a are achieved by X-ray molecular analysis.     

Trapping of carbamic acid species with (trimethylsilyl)diazomethane

Methoxycarbonylation of a variety of amines into the corresponding methyl carbamates was accomplished by allowing them to react with (trimethylsilyl)diazomethane TMSCHN₂ under bubbling of CO₂. The reaction was performed at room temperature for a period of ca. 2 h in benzene-MeOH (4/1 v/v), which was the solvent of choice. In this mixed solvent, undesirable bicarbonate is formed in equilibrium along with carbamate anion. Owing to the irreversibility in the esterification step by TMSCHN₂, however, the yield of methyl carbamate can reach very high.     

Trimethylsilyl fluorosulfonyldifluoroacetate (TFDA): a new, highly efficient difluorocarbene reagent

TFDA is readily prepared from the reaction of fluorosulfonyldifluoroacetic acid with trimethylsilyl chloride, and it is a very effective and efficient source of difluorocarbene for use in addition reactions to alkenes of a broad scope of reactivities. Acid-sensitive substrates may require an additional purification step involving treatment of the distilled TFDA with sufficient Et₃N to remove the acid impurity. Other trialkylsilyl fluorosulfonyldifluoroacetates can also be prepared, and they have been found to have reactivities similar to TFDA. The triethyl derivative, TEFDA is more convenient to prepare in a pure state and has similar reactivity to TFDA. Thus, it may prove to be a superior reagent.     

TG-DTA study on the lanthanoid trifluoromethanesulfonate complexes

The thermal decomposition of the lanthanoid trifluoromethanesulfonate (triflate) complexes {Ln(CF₃SO₃)₃·9H₂O; Ln=La-Lu{ was studied by TG and DTA methods. From the endothermic and exothermic data of Ln(CF₃ SO₃)3·9H₂O complexes, pyrolysis behavior of the complexes is classified into three groups: 1) La-Nd salts, 2) Sm-Ho salts, 3) Er-Lu salts. It has also shown that all the final decomposition products were found to result in the formation of LnF₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

Expeditious and efficient synthesis of Strecker’s α-aminonitriles catalyzed by sulfated polyborate

A straightforward, mild, efficient, and environmentally benign protocol for a three-component Strecker reaction of aldehydes or ketones, amines, and trimethylsilyl cyanide catalyzed by sulfated polyborate has been described to afford α-aminonitriles under solvent-free reaction conditions. The major advantages of the present method are excellent yields, shorter reaction time, simple experimental procedure, easy workup procedure, recyclability of the catalyst, solvent-free reaction conditions and ability to tolerate a variety of functional groups which gives economical as well as ecological rewards.     

Zirconium catalyzed amide formation without water scavenging

A scalable homogeneous metal‐catalyzed protocol for direct amidation of carboxylic acids is presented. The use of 2–10 mol% of the commercially available Zr(Cp)₂(OTf)₂·THF results in high yields of amides at moderate temperature, using an operationally convenient reaction protocol that circumvents the use of water scavenging techniques.     

Synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)nfluoren-9-one and 9-(p-methoxyphenyl)-9-methyl derivatives: optical properties

2,7-Substituted 9-fluorenones and 9,9-disubstituted fluorene have been synthesized and their fluorescence properties analyzed. The synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluoren-9-one (or the 9-(p-methoxyphenyl)-9-methyl) structures was carried out by the heterocoupling reaction between the 2,7-di(halo)fluoren-9-one (or 2,7-dibromo-9-(p-methoxyphenyl)-9-methylfluorene) and p-trimethylsilylethynyl(phenylethynyl)_n (n=1,2), catalyzed by the dichloro bis(triphenylphosphine)palladium and cuprous iodide system, in a divergent synthesis.The π-extended conjugated compounds exhibit fluorescence radiation emission (blue light-emitting), with important quantum yield for the 9-(p-methoxyphenyl)-9-methyl-2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluorenes which increases with the conjugation.