Attempted 1,3-trimethylsilyl migration in Me3Si?PSN?R system

A dimer of thioxo-N-t-butylimino(trimethylsiloxy)-phosphorane 5 has been prepared by reaction of tris(trimethylsilyl) phosphine with N-sulfinyl-N-tert-butylamine. The structure of 5 has been confimed by X-ray analysis data. 1-Aza-2-thia-3-phosphaallene 1 , thiaphosphaziridine 3 , iminophosphine P-sulfide 4 are postulated as intermediates of the reaction studied.     

B?H,C?H,and B?C Bond Activation: The Role of Two Adjacent Agostic Interactions

Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐B_sp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH₂P₂” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H₂ and boranes.     

Decomposition of 1,1‐dimethyl‐1‐silacyclobutane on a tungsten filament—evidence of both ring C?C and ring Si?C bond cleavages

The decomposition of 1,1‐dimethyl‐1‐silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time‐of‐flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1‐dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si? CH₃ bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C? C bond and a ring Si? C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C? C bond is dominant over that of propene via an initial cleavage of a ring Si? C bond. When the collision‐free condition is voided, secondary reactions in the gas‐phase produce various methyl‐substituted 1,3‐disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3‐tetramethyl‐1,3‐disilacyclobutane originated from the dimerization of 1,1‐dimethylsilene. Copyright © 2010 John Wiley & Sons, Ltd.     

Ab Initio energetics of Si?O bond cleavage

A multilevel approach that combines high‐level ab initio quantum chemical methods applied to a molecular model of a single, strain‐free Si O Si bridge has been used to derive accurate energetics for Si O bond cleavage. The calculated Si O bond dissociation energy and the activation energy for water‐assisted Si O bond cleavage of 624 and 163 kJ mol⁻¹, respectively, are in excellent agreement with values derived recently from experimental data. In addition, the activation energy for H₂O‐assisted Si O bond cleavage is found virtually independent of the amount of water molecules in the vicinity of the reaction site. The estimated reaction energy for this process including zero‐point vibrational contribution is in the range of −5 to 19 kJ mol⁻¹. © 2017 Wiley Periodicals, Inc.     

Catalytic C?C,C?N,and C?O Ullmann‐Type Coupling Reactions

Copper‐catalyzed Ullmann condensations are key reactions for the formation of carbon–heteroatom and carbon–carbon bonds in organic synthesis. These reactions can lead to structural moieties that are prevalent in building blocks of active molecules in the life sciences and in many material precursors. An increasing number of publications have appeared concerning Ullmann‐type intermolecular reactions for the coupling of aryl and vinyl halides with N, O, and C nucleophiles, and this Minireview highlights recent and major developments in this topic since 2004.     

Amide‐Directed Tandem C?C/C?N Bond Formation through C?H Activation

The transformation of C? H bonds into other chemical bonds is of great significance in synthetic chemistry. C? H bond‐activation processes provide a straightforward and atom‐economic strategy for the construction of complex structures; as such, they have attracted widespread interest over the past decade. As a prevalent directing group in the field of C? H activation, the amide group not only offers excellent regiodirecting ability, but is also a potential C? N bond precursor. As a consequence, a variety of nitrogen‐containing heterocycles have been obtained by using these reactions. This Focus Review addresses the recent research into the amide‐directed tandem C? C/C? N bond‐formation process through C? H activation. The large body of research in this field over the past three years has established it as one of the most‐important topics in organic chemistry.     

Copper‐Catalyzed Radical/Radical C?H/P?H Cross‐Coupling: α‐Phosphorylation of Aryl Ketone O‐Acetyloximes

The selective radical/radical cross‐coupling of two different organic radicals is a great challenge due to the inherent activity of radicals. In this paper, a copper‐catalyzed radical/radical C H/P H cross‐coupling has been developed. It provides a radical/radical cross‐coupling in a selective manner. This work offers a simple way toward β‐ketophosphonates by oxidative coupling of aryl ketone o‐acetyloximes with phosphine oxides using CuCl as catalyst and PCy₃ as ligand in dioxane under N₂ atmosphere at 130 °C for 5 h, and yields ranging from 47 % to 86 %. The preliminary mechanistic studies by electron paramagnetic resonance (EPR) showed that, 1) the reduction of ketone o‐acetyloximes generates iminium radicals, which could isomerize to α‐sp³‐carbon radical species; 2) phosphorus radicals were generated from the oxidation of phosphine oxides. Various aryl ketone o‐acetyloximes and phosphine oxides were suitable for this transformation.     

Synthesis and properties of new Si?H-containing polymers

Poly[(methylsilylene)ethynylene] ( 1 ) and poly[2,5-thiophenediyl(methylsilylene)] ( 2 ) are prepared in good yields. Thermogravimetric analysis and differential scanning calorimetry indicate the Si H group to increase the pyrolysis residue yields. Gelation was achieved from polymer 1 to get improved preceramic materials. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2275–2282, 1998     

The Morita?Baylis?Hillman Reaction of Chiral Highly Oxygenated Cyclopent‐2‐enones

The Morita? Baylis? Hillman (MBH) reactions of (4S,5R,7R,8R)‐ and (4R,5R,7R,8R)‐4‐hydroxy‐7,8‐dimethoxy‐7,8‐dimethyl‐6,9‐dioxaspiro[4.5]dec‐2‐en‐1‐ones ( 2 and 3 , resp.) with aldehydes using various catalysts were studied. A combination of Bu₃P/phenol in THF was found being optimum conditions giving the corresponding MBH adducts with high diastereoisomeric ratios. After separation, each stereomerically pure isomer of the MBH adducts was subjected to hydrolysis employing 1% aq. CF₃COOH (TFA) in a water bath of an ultrasonic cleaner to afford the corresponding polyhydroxylated cyclopentenones in good yields.     

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of N?H Imines and Alkynes by C?H/N?H Activation

Described herein is a manganese‐catalyzed dehydrogenative [4+2] annulation of N H imines and alkynes, a reaction providing highly atom‐economical access to diverse isoquinolines. This transformation represents the first example of manganese‐catalyzed C H activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H₂ as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition‐metal‐catalyzed C H activation. Mechanistic studies revealed the five‐membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.     

Oxindole Synthesis by Direct Coupling of C?H and C?H Centers

An sp ² /sp ³ get‐together : A novel and efficient method can be used to synthesize 3,3‐disubstitued oxindoles by the direct intramolecular oxidative coupling of an aryl C? H and a C? H center (see scheme; DMF=N,N‐dimethylformamide).

     

Synthesis of 1,3‐Diamines Through Rhodium‐Catalyzed C?H Insertion

A grand opening : N‐Boc‐N‐alkylsulfamides are effective substrates for the title transformation. Oxidative cyclization is highly chemoselective as well as being both stereospecific and diastereoselective. With the advent of new protocols that facilitate ring opening of the six‐membered‐ring heterocyclic products, access to differentially protected 1,3‐diamines has been made possible (see scheme).

     

Aldehyde‐Assisted Ruthenium(II)‐Catalyzed C?H Oxygenations

Versatile ruthenium(II) complexes allow for site‐selective C H oxygenations with weakly‐coordinating aldehydes. The challenging C H functionalizations proceed with high chemoselectivity by rate‐determining C H metalation. The new method features an ample substrate scope, which sets the stage for the step‐economical preparation of various bioactive heterocycles.     

Synthesis of 1,3‐Diamines Through Rhodium‐Catalyzed C?H Insertion

Schließen und öffnen : N‐Boc‐N‐alkylsulfamide sind geeignete Substrate für die Titelreaktion. Die oxidative Cyclisierung im ersten Schritt ist hoch chemoselektiv sowie stereospezifisch und diastereoselektiv. Mit neuen Verfahren zur Öffnung der dabei erhaltenen Sechsringheterocyclen werden unterschiedlich geschützte 1,3‐Diamine zugänglich (siehe Schema).

     

Alkyne Insertion into the M?P and M?H Bonds (M=Pd,Ni, Pt,and Rh): A Theoretical Mechanistic Study of the C?P and C?H Bond‐Formation Steps

In hydrogen‐metal‐phosphorus (H M P) transition metal complexes (proposed as intermediates of H P bond addition to alkynes in the catalytic hydrophosphorylation, hydrophosphinylation, and hydrophospination reactions), alkyne insertion into the metal‐hydrogen bond was found much more facile compared to alkyne insertion into the metal‐phosphorus bond. The conclusion was verified for different metals (Pd, Ni, Pt, and Rh), ligands, and phosphorus groups at various theory levels (B3LYP, B3PW91, BLYP, MP2, and ONIOM). The relative reactivity of the metal complexes in the reaction with alkynes was estimated and decreased in the order of Ni>Pd>Rh>Pt. A trend in relative reactivity was established for various types of phosphorus groups: PR₂>P(O)R₂>P(O)(OR)₂, which showed a decrease in rate upon increasing the number of the oxygen atoms attached to the phosphorus center.     

Palladium(II)‐Catalyzed C?H Activation/C?C Cross‐Coupling Reactions: Versatility and Practicality

Pick your Pd partners : A number of catalytic systems have been developed for palladium‐catalyzed C? H activation/C? C bond formation. Recent studies concerning the palladium(II)‐catalyzed coupling of C? H bonds with organometallic reagents through a Pd^II/Pd⁰ catalytic cycle are discussed (see scheme), and the versatility and practicality of this new mode of catalysis are presented. Unaddressed questions and the potential for development in the field are also addressed.