Chemoselective Protection of Hydroxyl Groups and Deprotection of Silyl Ethers

Summary.  Trimethylsilylation of alcohols and phenols is carried out using hexamethyldisilazane and LiClO₄ under microwave irradiation and neutral conditions. The deprotection of silyl ethers is carried out similarly using natural kaolinitic clay and a few drops of water. Received March 1, 2001. Accepted (revised) April 17, 2001     

Synthesis of 3-substituted 2-cyclohexenones through umpoled functionalization

A new protocol to obtain 3-substituted 2-cyclohexenones, was developed by reversing the chemical reactivity of 2-cyclohexenone. One-pot synthesis of 3-substituted 2-cyclohexenones can be achieved by treatment of 3-phenylthiosilyl enol ether with a mixture of t-BuLi/HMPA that allows hydrogen-selective exchange in presence of reactive electrophiles such as aldehydes, ketones and alkyl halides. This affords the corresponding product in moderate overall yield, after silyl enol ether cleavage and concomitant thiophenol elimination initiated with TBAF.     

Cobalt-catalyzed regioselective [3+2] annulation of ortho-formyl and acetyl substituted phenylboronic acids with alkynes

Treatment of alkynes with ortho-formyl and acetyl phenylboronic acids in the presence of a cobalt catalyst resulted in the formation of 2,3-disubstituted indenols in good yields. When aryl silyl alkynes were used, 2-aryl-3-silyl indenols were obtained regioselectively in good yields.     

On Rectifiable Curves in the Plane

This paper gives a formula of integral for the rectifiable curves in the plane by the Hausdorff fractional derivation and integral. Received August 10, 1999, Revised December 27, 1999, Accepted January 14, 2000     

Synthesis of 5‐(Arylselanyl)‐2‐(arylsulfanyl)benzoates by [3+3] Cyclocondensation of 3‐(Arylsulfanyl)‐1‐(silyloxy)buta‐1,3‐dienes with 2‐(Arylselanyl)‐3‐(silyloxy)alk‐2‐en‐1‐ones

Functionalized 5‐(arylselanyl)‐2‐(arylsulfanyl)benzoates were prepared by [3+3] cyclocondensation of 3‐(arylsulfanyl)‐1‐(silyloxy)buta‐1,3‐dienes with 2‐(arylselanyl)‐3‐(silyloxy)‐alk‐2‐en‐1‐ones.     

Strong influence of intramolecular Si⋯O proximity on reactivity: Systematic molecular structure,solvolysis, and mechanistic study of cyclic N-trimethylsilyl carboxamide derivatives

A comparative alcoholysis study of N-silylated derivatives of simple heterocyclic carboxamides (lactams, imides, ureas) is presented. The second-order rate constant values span a range as wide as three orders of magnitude. On the basis of DFT calculations, a good correlation between reactivity and the Si?O distance was found within each family of compounds. The viability of two different reaction pathways was evaluated using a detailed computational mechanistic study of the methanolysis of cyclic urea homologues. Peculiarities in the single-crystal X-ray diffraction structures of the trimethylsilyl and trimethylsiloxy phthalimides are also discussed.     

Synthesis of organosilyl compounds-containing 1,2,4,5-tetraaryl imidazoles sonocatalyzed by M/SAPO-34 (M = Fe,Co, Mn,and Cu) nanostructures

The one-step synthesis of silylated 1,2,4,5-tetraaryl imidazoles by use of a series of M/SAPO-34 (M: Fe, Co, Mn, and Cu) nanocatalysts and subsequent silylation reactions is described. Cu/SAPO-34 catalyst has the highest activity in improving the efficiency of the heterogeneous cyclo-condensation of an aldehyde, benzil, ammonium acetate and a primary aromatic amine in water under ultrasonic irradiation. Some of imidazole derivatives are studied with a view to the synthesis of a series of new, multi-substituted imidazoles containing organosilyl groups including carbosilanes (Si–C) and silyl ethers (Si–O).     

Derivatization of Tris(trimethylsilyl)heptaphosphane

Through SiP bond cleavage, the reaction of P₇(SiMe₃)₃ with one equivalent of KO^tBu or LiO^tBu afforded different isomers of the heptaphosphanide anion [P₇(SiMe₃)₂]⁻. With LiO^tBu, concomitant inversion at an equatorial (silylated) phosphorus atom occurred and the C_s symmetric isomer characterized by a mirror plane formed. With KO^tBu, inversion did not occur and the resulting asymmetric anion with C₁ symmetry formed. With NaO^tBu, a mixture of both isomers was obtained. The symmetries and structures of the anions were elucidated with ³¹P{¹H} and ²⁹Si{¹H} NMR spectroscopy, and relative stabilities were calculated employing the B3LYP/6-31+G* method.The reaction of KP₇(SiMe₃)₂ or LiP₇(SiMe₃)₂ with 1,2-dichlorotetramethyldisilane led to (SiMe₃)₂P₇SiMe₂SiMe₂P₇(SiMe₃)₂, a molecule composed of two P₇-cages connected by a disilane bridge. It can also be obtained through silyl exchange using P₇(SiMe₃)₃ and ClMe₂SiSiMe₂Cl. The compound was characterized with ³¹P and ²⁹Si-NMR spectroscopy and elemental analysis. Treatment of P₇(SiMe₃)₃ with HypCl (Hyp = hypersilyl = Si(SiMe₃)₃) in DME led to the quantitative formation of Hyp₂P₇SiMe₃. Single crystal X-ray diffraction as well as ³¹P and ²⁹Si-NMR spectroscopy proves the presence of a heteroleptically substituted heptaphosphane cage.Quantum chemical HF and B3LYP/6-31G* calculations of equilibrium structures for the two possible isomers of P₇(SiMe₃)₃ (sym and asym) reveal that asym is destabilized by about 30-40 kJ mol⁻¹, which explains why its formation could not be observed. The phosphorus inversion barrier for the sym → asym transition is calculated as 60-70 kJ mol⁻¹.     

Bis(trimethylsilyl)diimine: Preparation,Structure, and Reactivity

The highly reactive compound bis(trimethylsilyl)diimine (BSD), which was first prepared by oxidation of lithium tris(trimethylsilyl)hydrazide, is light blue, sensitive to thermolysis and hydrolysis, and ignites spontaneously in air. On the basis of electron transfer, acid-base, or free-radical reactions, it acts in particular as a (preparatively useful) redox system and as an agent for the introduction of azo groups. Redox reactions lead by oxidation or reduction of the other reactant through two oxidation stages to hydrazine derivatives or molecular nitrogen, and in the case of electrochemical reduction, to BSD radical-anions. Azo-group transfers, on the other hand, yield new inorganic azo compounds with no change in the oxidation state of the diimine group.