Search

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A copper‐catalyzed C4‐selective addition of silicon nucleophiles released from an Si−B reagent to prochiral pyridinium triflates is reported. The dearomatization proceeds with excellent enantioselectivity using Cu(CH3CN)4PF6 as the precatalyst and (R,R)‐Ph‐BPE (1,2‐bis[(2R,5R)‐2,5‐diphenylphospholan‐1‐yl]ethane) as the chiral ligand. A carbonyl group at C3 is required for this, likely acting a weak donor group to preorganize and direct the nucleophilic attack towards C4. The resulting 4‐silylated 1,4‐dihydropyridines can be further converted into functionalized piperidine derivatives. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biocatalytic nucleoside (trans‐)glycosylations catalyzed by nucleoside phosphorylases have evolved into a practical and convenient approach to the preparation of modified nucleosides, which are important pharmaceuticals for the treatment of various cancers and viral infections. However, the obtained yields in these reactions are generally determined exclusively by the innate thermodynamic properties of the nucleosides involved, hampering the biocatalytic access to many sought‐after target nucleosides. We herein report an additional means for reaction engineering of these systems. We show how apparent equilibrium shifts in phosphorolysis and glycosylation reactions can be effected through entropically driven, biased esterification of nucleosides and ribosyl phosphates with inorganic borate. Our multifaceted analysis further describes the kinetic implications of this in situ reactant esterification for a model phosphorylase. [ABSTRACT FROM AUTHOR]

White phosphorus (P4) undergoes degradation to P2 moieties if exposed to the new N,N‐bis(silylenyl)aniline PhNSi21 (Si=Si[N(tBu)]2CPh), furnishing the first isolable 2,5‐disila‐3,4‐diphosphapyrrole 2 and the two novel functionalized Si=P doubly bonded compounds 3 and 4. The pathways for the transformation of the non‐aromatic 2,5‐disila‐3,4‐diphosphapyrrole PhNSi2P22 into 3 and 4 could be uncovered. It became evident that 2 reacts readily with both reactants P4 and 1 to afford either the polycyclic Si=P‐containing product [PhNSi2P2]2P23 or the unprecedented conjugated Si=P−Si=P−Si=NPh chain‐containing compound 4, depending on the employed molar ratio of 1 and P4 as well as the reaction conditions. Compounds 3 and 4 can be converted into each other by reactions with 1 and P4, respectively. All new compounds 1–4 were unequivocally characterized including by single‐crystal X‐ray diffraction analysis. In addition, the electronic structures of 2–4 were established by Density Functional Theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tris(pentafluorophenyl)borane has been found to catalyze the two‐fold C(sp3)−H silylation of various trialkylamine derivatives with dihydrosilanes, furnishing the corresponding 4‐silapiperidines in decent yields. The multi‐step reaction cascade involves amine‐to‐enamine dehydrogenation at two alkyl residues and two electrophilic silylation reactions of those enamines, one inter‐ and one intramolecular. [ABSTRACT FROM AUTHOR]

The preparation and NMR spectroscopic characterization of a family of axial chiral, sulfur‐stabilized silicon cations is reported. These silicon Lewis acids have been applied as catalysts in difficult enantioselective Diels–Alder reactions of cyclohexa‐1,3‐diene and representative chalcone derivatives. To gain better understanding of the relevant structural elements in these catalysts, their silepine backbone and the aryl thioether group have been systematically modified. These efforts have led to an improved catalyst that induces 53 % ee for chalcone and even 65 % ee for a more hindered derivative. These cyclohexa‐1,3‐diene Diels–Alder reactions are endo selective. However, the corresponding cyclopentadiene Diels–Alder reactions predominantly yield the exo cycloadducts with no enantioinduction. [ABSTRACT FROM AUTHOR]

The transition-metal-free hydroboration of various alkenes with pinacolborane (HBpin) initiated by tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF 3) is reported. The choice of the boron Lewis acid is crucial as the more prominent boron Lewis acid tris(pentafluorophenyl)- borane (B(C6F5)3) is reluctant to react. Unlike B(C6F5)3, BArF 3 is found to engage in substituent redistribution with HBpin, resulting in the formation of ArFBpin and the electron-deficient diboranes [H2BArF]2 and [(ArF)(H)B(µ-H)2BArF 2]. These in situ-generated hydroboranes undergo regioselective hydroboration of styrene derivatives as well as aliphatic alkenes with cis diastereoselectivity. Another ligand metathesis of these adducts with HBpin subsequently affords the corresponding HBpin-derived anti-Markovnikov adducts. The reactive hydroboranes are regenerated in this step, thereby closing the catalytic cycle. [ABSTRACT FROM AUTHOR]

Chronic phantom pain has been found in up to 78% of limb amputees and is a major complication of limb amputation. Less is known about phantom phenomena after the amputation of other, i.e. visceral, parts of the body. In a retrospective design, we identified 539 patients in whom one testis was removed between 1995 and 2005. The operative technique was a unilateral standard radical inguinal orchiectomy. The underlying pathology in all cases was a testicular germ cell tumour. All patients received a detailed questionnaire asking about the occurrence of phantom testis pain (pain felt in the removed testis), phantom testis sensations (non-painful sensations as if the removed testis was still intact) and hallucinations (illusionary perceptions on the removed testis). Furthermore, we asked about the occurrence and clinical presentation of pain before and after surgery and about pre-operative testicular pain. Out of 238 respondents, 125 patients (53%) reported any kind of phantom experience. The prevalence of phantom testis pain was 25% (60/238), non-painful phantom sensations 16% (37/238) and male gonad hallucinations 12% (28/238). Patients with phantom symptoms reported pre-operative pain in the removed testis more often than patients without phantom symptoms. This study presents first data on the clinical characteristics and possible mechanisms of the phantom testis syndrome after surgical removal of one testis. [ABSTRACT FROM AUTHOR]

Although ethers are common in secondary natural products, they are an underrepresented functional group in primary metabolism. As such, there are comparably few enzymes capable of constructing ether bonds in a general fashion. However, such enzymes are highly sought after for synthetic applications as they typically operate with higher regioselectivity and under milder conditions than traditional organochemical approaches. To expand the repertoire of well characterized ether synthases, we herein report on a promiscuous archaeal prenyltransferase from the scarcely researched family of geranylgeranylglyceryl phosphate synthases (GGGPSs or G3PSs). We show that the ultrastable Archaeoglobus fulgidus G3PS makes various (E)‐ and (Z)‐configured prenyl glycerol ethers from the corresponding pyrophosphates while exerting perfect control over the configuration at the glycerol unit. Based on experimental and computational data, we propose a mechanism for this enzyme which involves an intermediary prenyl carbocation equivalent. As such, this study provides the fundamental understanding and methods to introduce G3PSs into the biocatalytic alkylation toolbox. [ABSTRACT FROM AUTHOR]

Tris(pentafluorophenyl)borane has been found to catalyze the two‐fold C(sp3)−H silylation of various trialkylamine derivatives with dihydrosilanes, furnishing the corresponding 4‐silapiperidines in decent yields. The multi‐step reaction cascade involves amine‐to‐enamine dehydrogenation at two alkyl residues and two electrophilic silylation reactions of those enamines, one inter‐ and one intramolecular. [ABSTRACT FROM AUTHOR]

Es wurde gefunden, dass Tris(pentafluorphenyl)boran die zweifache C(sp3)‐H‐Silylierung von mehreren Trialkylaminderivaten mit Dihydrosilanen katalysiert und die entsprechenden 4‐Silapiperidine in annehmbaren Ausbeuten ergibt. Die mehrstufige Reaktionsabfolge beinhaltet die Dehydrierung des Amins zum Enamin an zwei Alkylresten und zwei elektrophile (eine inter‐ und eine intramolekular) Silylierungen jener Enamine. [ABSTRACT FROM AUTHOR]