Robby Vroemans

Abstract

The homolytic cleavage of the P^V(O)–P^III bond in tetraphenyldiphosphine monoxide simultaneously provides both pentavalent and trivalent phosphorus-centered radicals with different reactivities. The method using V-40 as an initiator is successfully investigated for the regio- and stereoselective phosphinylphosphination of terminal alkynes giving the corresponding trans-isomers of 1-diphenylphosphinyl-2-diphenylthiophosphinyl-1-alkenes in good yields. The protocol can be applied to a wide variety of terminal alkynes including both alkyl- and arylalkynes.

Beilstein J. Org. Chem. 2021, 17, 866–872. doi:10.3762/bjoc.17.72

Isodesmic C–H functionalization reactions are extremely rare. Herein we report the first Pd(II)-catalyzed isodesmic C–H iodination of arenes using 2-nitrophenyl iodides as the mild iodinating reagents. Unusual C–I reductive elimination occurred in preference to competing C–C coupling in this reaction. Assisted by aliphatic carboxyl directing groups, a range of hydrocinnamic acids and related arenes could be selectively iodinated at either meta- or ortho-positions of the phenyl ring. Remote diastereoselective C–H activation was also promising. This method may open up a new way to iodinate challenging substrates.

Synthesis
DOI: 10.1055/a-1472-7578

A new synthetic methodology has been developed for the synthesis of sulfinate alkyl and aryl esters. The methodology involves the combination of p-toluenesulfinic acid and 1,1′-carbonyldiimidazole (CDI) to create the putative reagent sulfinylimidazole. The process spontaneously releases carbon dioxide upon the addition of the CDI to the acid suggesting the rapid formation of the proposed reagent. Reaction of this reagent with a series of alcohols (primary, secondary, and tertiary) afforded the corresponding sulfinate alkyl esters in good to excellent yields by the addition of alcohols. It was also possible to form the related sulfinate aryl esters by treating the proposed sulfinylimidazole with selected phenols (phenol, p-tert-butylphenol, and thymol). The aryl esters were formed in excellent conversion based on analysis of the 500 MHz 1H NMR spectra of the crude reaction mixtures.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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The development of catalytic enantioselective isocyanide‐based reactions leading to products, which are valuable in organic synthesis, pharmacological chemistry, and materials science is currently of great interest. Recent achievements in this rapidly growing area according to the reaction types, with special attention being paid to the advantages, limitations, possible mechanisms, and synthetic applications of each reaction is given in the Review by Y.‐L. Liu et al. on page 6598.

A palladium-catalyzed remote phosphonylation for the indole C4- and C6-positions was achieved by a radical approach. The preliminary mechanistic studies indicated that the reactions may proceed via a C7-palladacycle/remote-activation process.

Abstract

Palladium-catalyzed direct C−H activation of indole benzenoid moiety has been achieved in the past decade. However, palladium-catalyzed remote C−H activation of indoles is rare. Herein, we report a challenging palladium-catalyzed remote C4-H phosphonylation of indoles by a radical approach. The method provides access to a series of C4-phosphonylated indoles, including tryptophan and tryptophan-containing dipeptides, which are typically inaccessible by direct C4-H activation due to its heavy reliance on C3 directing groups. Notably, unexpected C6-phosphonylated indoles were obtained through blocking of the C4 position. The preliminary mechanistic studies indicated that the reactions may proceed via a C7-palladacycle/remote-activation process. Based on the strategy, examples of remote C4-H difluoromethylation with BrCF₂COOEt are also presented, suggesting that the strategy may offer a general blueprint for other cross-couplings.

Non‐coordinated phenolate anions: By deprotonation of phenol with the strong tetraphosphazene Schwesinger base a salt of the so far unknown free phenolate anion was formed. In contrast to that, the deprotonation with a less basic monophosphazene base leads to a phenol–phenolate salt with an additional hydrogen bond to the phosphazenium cation. Applying electron‐rich phenolate salts we further present the two‐electron reduction of SF₆ leading to [SF₅]⁻ and F⁻ salts.

Abstract

The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol–phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H₅C₆‐O]⁻. The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol‐phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of −0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF₆. The performed two‐electron reduction of SF₆ leads to phosphazenium pentafluorosulfanide ([SF₅]⁻) and fluoride salts.

The extremely electron-deficient tetratrifluorocatechol is synthesized and installed at silicon, providing a Lewis superacid that ranks among the strongest fluoride ion acceptors accessible in the condensed phase. The compound enables silicon-catalyzed deoxygenation of ketones, aldehydes, amides and phosphine oxides and the first silicon catalyzed carbonyl-olefin metathesis.

Abstract

Given its earth abundance, silicon is ideal for constructing Lewis acids of use in catalysis or materials science. Neutral silanes were limited to moderate Lewis acidity, until halogenated catecholato ligands provoked a significant boost. However, catalytic applications of bis(perhalocatecholato)silanes were suffering from very poor solubility and unknown deactivation pathways. In this work, the novel per(trifluoromethyl)catechol, H₂cat^CF3, and adducts of its silicon complex Si(cat^CF3)₂ (1) are described. According to the computed fluoride ion affinity, 1 ranks among the strongest neutral Lewis acids currently accessible in the condensed phase. The improved robustness and affinity of 1 enable deoxygenations of aldehydes, ketones, amides, or phosphine oxides, and a carbonyl-olefin metathesis. All those transformations have never been catalyzed by a neutral silane. Attempts to obtain donor-free 1 attest to the extreme Lewis acidity by stabilizing adducts with even the weakest donors, such as benzophenone or hexaethyl disiloxane.

Although much can be deduced from fossils alone, estimating abundance and preservation rates of extinct species requires data from living species. Here, we use the relationship between population density and body mass among living species combined with our substantial knowledge of Tyrannosaurus rex to calculate population variables and preservation rates for postjuvenile T. rex. We estimate that its abundance at any one time was ~20,000 individuals, that it persisted for ~127,000 generations, and that the total number of T. rex that ever lived was ~2.5 billion individuals, with a fossil recovery rate of 1 per ~80 million individuals or 1 per 16,000 individuals where its fossils are most abundant. The uncertainties in these values span more than two orders of magnitude, largely because of the variance in the density–body mass relationship rather than variance in the paleobiological input variables.