Synthesis and Characterization of New N‐Heterocyclic Silylazides

Three novel pyridine functionalized N‐heterocyclic silanes, bearing chloride and azide moieties, were synthesized and characterized by NMR spectroscopy (¹H, ¹³C, ²⁹Si), mass spectrometry, elemental analysis, and single‐crystal XRD. The molecular structures show a comparably strong dative interaction of the pyridine‐N with the Si center, formally inducing a penta‐coordination arrangement at the silicon(IV). Under appropriate conditions, the silylazides, presented in this work, might be able to thermo‐ or photolytically liberate gaseous nitrogen giving rise to a promising synthetic option to access a variety of new transition metal silylene complexes with potential applications in various catalytic reactions.     

Synthesis and Structure of Tetraethynylsilane and Its Silylated Derivatives

The known tetrakis((trimethylsilyl)ethynyl)silane was prepared and deprotected. By using trifluoromethanesulfonic acid, the smooth stepwise desilylation of the starting material was achieved, and all of the partially protected and the fully deprotected species were isolated by sublimation. Crystal structures of all of the partially and the fully deprotected species were obtained. None of the compounds is thermally sensitive. Attempts to explosively decompose these species upon heating failed.     

Asymmetric Catalysis with Silicon‐Based Cuprates: Enantio‐ and Regioselective Allylic Substitution of Linear Precursors

An enantio‐ and regioselective allylic silylation of linear allylic phosphates that makes use of catalytically generated cuprate‐type silicon nucleophiles is reported. The method relies on soft bis(triorganosilyl) zincs as silicon pronucleophiles that are prepared in situ from the corresponding hard lithium reagents by transmetalation with ZnCl₂. With a preformed chiral N‐heterocyclic carbene–copper(I) complex as catalyst, exceedingly high enantiomeric excesses are achieved. The new method is superior to existing ones using a silicon–boron reagent as the source of the silicon nucleophile.     

From an α‐Functionalized Silicon‐Stereogenic N,O‐Silane to a Monomeric and Tetracoordinate tBuLi Adduct with Lithium‐Centered Chirality

Donor‐functionalized silanes with stereogenic silicon centers are extremely rare. A convenient stereocontrolled route to a nitrogen‐oxygen‐functionalized silicon‐chiral compound with an additional aminomethyl function is presented. This silane was directly achieved in stereochemically pure form by a simple nucleophilic substitution reaction. Owing to the unique asymmetry of this silane and the presence of three donor functions, the first monomeric butyllithium compound with lithium‐centered chirality could be isolated; the configuration was assigned by X‐ray crystallography. This [silane? tBuLi] complex undergoes an unexpected deprotonation/stereospecific substitution sequence in toluene, leading to the development of a convenient one‐pot synthesis of a functionalized silicon‐chiral benzylsilane, which proceeds with inversion of configuration and complete preservation of the stereochemical integrity at silicon.     

Lewis‐Base‐Mediated Diastereoselective Silylations of Alcohols: Synthesis of Silicon‐Stereogenic Dialkoxysilanes Controlled by Chiral Aryl BINMOLs

In the past years, stereoselective functionalizations of hydroxyl groups of alcohol substrates with chlorosilanes leading to silyl ether formation have evolved from a functional‐group protection to an enantioselective synthetic strategy. This work comprises a controlled desymmetrization of dichlorosilanes by using a family of structurally specific chiral diols, chiral 1,1′‐binaphthalene‐2‐α‐arylmethanol‐2′‐ol (Ar‐BINMOL). This process led to the facile construction of silicon‐stereogenic organosilicon compounds with high yields and good diastereoselectivities. In addition, the diasteroselective silylation of chiral diols might not only be of interest for the development of highly stereoselective nucleophilic silylation, but also shed light on the construction of novel chiral phosphine ligands bearing a silicon‐stereogenic center.     

Temporary Silicon‐Tethered Ring‐Closing Metathesis: Recent Advances in Methodology Development and Natural Product Synthesis

Temporary silicon‐tethered ring‐closing metathesis represents an important cross‐coupling strategy for the formation of medium‐sized silacycles. These intermediates are valuable synthons in organic synthesis due to their propensity to undergo a facile refunctionalization through protodesilylation, oxidation, silane‐group transfer or transmetallation. A particularly attractive utility of this methodology is an application in the synthesis of biologically important natural products. The purpose of this review article is to highlight the recent progress in methodology development and its strategic application toward the target‐directed synthesis.     

Silicon‐Directed Rhenium‐Catalyzed Allylic Carbaminations and Oxidative Fragmentations of γ‐Silyl Allylic Alcohols

A highly regioselective allylic substitution of β‐silyl allylic alcohols has been achieved that provides the branched isomer as a single product. This high level of regiocontrol is achieved through the use of a vinyl silane group that can perform a Hiyama coupling providing 1,3‐disubstituted allylic amines. An unusual oxidative fragmentation product was also observed at elevated temperature that appears to proceed by a Fleming–Tamao‐type oxidation–elimination pathway.     

Novel Ladder π‐Conjugated Materials—Sila‐Pentathienoacenes: Synthesis,Structure, and Electronic Properties

A novel series of ladder π‐conjugated materials—sila‐pentathienoacenes ( Si‐PTA ) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on molecular packing. A densely packed structure with an interfacial distance of about 3.66 Å between the adjacent molecules is observed for the compound with shorter alkyl chains. However, a large interfacial distance (7.99 Å) is obtained for another compound because of the insertion of long alkyl chains between two planes. The investigation of the optical and electrochemical properties shows that the silylene bridge incorporated into the pentathienoacene framework exerts a clear effect on the electronic properties by the σ*–π* conjugation. Although only a slight enhancement is observed for the HOMO levels, with respect to that of pentathienoacene, the LUMO levels are significantly lowered. The observed electronic properties are consistent with the theoretical calculations.     

Desymmetrization‐Oriented Enantioselective Synthesis of Silicon‐Stereogenic Silanes by Palladium‐Catalyzed C−H Olefinations

A palladium‐catalyzed chelation‐assisted enantioselective C?H olefination of symmetrically diaryl‐substituted tetraorganosilicon derivatives was developed, enabling the generation of nitrogen‐containing silicon‐stereogenic tetraorganosilicon compounds with modest to good yields and good to excellent enantioselectivities (up to 95.5:4.5 e.r.). The Thorpe–Ingold effect exerted by the substituents on silicon was observed to have a profound influence on formation of olefinated products which were further converted into other relevant chiral organosilanes without the loss of enantiomeric purity, thus demonstrating the synthetic utility of the developed enantioselective olefination.     

Facile and Scalable Synthesis of Silicon‐Based Nanocomposites with Slitlike Nanopores: A Solid‐State Exfoliation Reaction Using Layered CaSi2

Silicon‐based nanocomposites with slitlike nanopores were prepared by heating a mixture of layered CaSi₂ and NiCl₂. The formation mechanism is based on a solid‐state exfoliation reaction wherein the formation of CaCl₂ promotes the extraction of Ca from CaSi₂, thereby exfoliating the layered structure. The nanocomposites showed anode capacity for lithium ion batteries up to 804 mA h g^?1.     

Selenium‐Containing Heterocycles from Isoselenocyanates: Synthesis of 1,3‐Selenazinane and 1,3‐Selenazinanone Derivatives

The reaction of the intermediate ketene N,Se‐hemiacetal 3 , prepared from cyanomethylene derivatives 1 by treatment with Et₃N and aryl isoselenocyanates 2 , with bis‐electrophiles 6, 7, 9 , and 11 in DMF affords tetrahydro‐1H‐1,3‐selenazine (=1,3‐selenazinane) derivatives 8, 10 , and 12 in good yield (Scheme 2 and Tables 1–3). Chemical and spectroscopic evidence for the structures of the new compounds are described. The structures of 8d and 12e are established by X‐ray crystallography (Figs. 1 and 2).     

Solid‐State Synthesis and Characterization of 2‐Thioxo‐4‐Imidazolidinone Derivatives

A new and efficient two‐step solid‐state synthesis method is described for 2‐thioxo‐4‐imidazolidinone from aryl isothiocyanate and free amino acid. This method requires only simple equipment and is easy to perform. The products reported were characterized on the basis of IR, MS, ¹H NMR, ¹³C NMR and elemental analysis.     

Silicon‐modified surfactants and wetting: I. Synthesis of the single components of Silwet L77 and their spreading performance on a low‐energy solid surface

Defined surfactants of general formula [(CH₃)₃SiO]₂CH₃Si(CH₂)₃(OCH₂CH₂)_3–9OCH₃, have been synthesized from the corresponding oligoethylene glycol monoallyl monomethyl ethers via hydrosilylation. The concentration‐dependent spreading performance on hydrophobized silicon wafers has been investigated and compared with that of Silwet L77. For the hexaethylene glycol derivative the highest initial spreading velocities and largest spreading areas were found. Since Silwet L77 spreads faster than all the other derivatives under investigation, a synergistic effect of different compounds is unlikely. Minor differences were found for handshaken and sonicated solutions. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis of Novel Biphenyltetrazole Derivatives Containing 5‐Methylisoxazole Substituted 1,2,4‐Triazole

An efficient route to synthesize the target compounds was developed. Fifteen new 5‐[4′‐(5‐isoxazol‐4‐aryl‐1,2,4‐triazol‐3‐yl‐sulfanylmethyl)‐biphenyl‐2‐yl]‐tetrazoles derivatives were synthesized. The structures of the new compounds synthesized were confirmed by elemental analyses and spectral data.