Hypervalent Compounds

A new class of fluorinated lactones was prepared by the intramolecular fluorocyclizations of unsaturated carboxylic acids using the stable fluoroiodane reagent in combination with AgBF4. This unique reaction incorporates a cyclization, an aryl migration and a fluorination all in one step. The fluoroiodane reagent, prepared easily from fluoride, can also be used without a metal catalyst to give moderate yields in just 1 h demonstrating that it is a suitable reagent for developing new 18 F-labelled radiotracers for PET imaging. Fluorinated heterocycles, which are highly-sought after building blocks for the pharmaceutical and agrochemical industries, can be accessed in a single step by the intramolecular fluorocyclization of alkenes. [1] -Butyrolactones are common structural motifs found in a variety of natural products that exhibit a wide range of biological properties (Figure ). [2] Since the benzyl-substituted -lactones 3 have shown anti-cancer and antiinflammatory activities, [3e] new synthetic strategies have been developed for their construction, [3] but as far as we are aware, no-one has prepared any fluorinated analogues.

A one pot room temperature synthesis of thionyl tetrafluoride (SOF4) from elemental fluorine (F2) and thionyl fluoride (SOF2) is reported. The selective decagram scale process (100 mmol) allows a quantitative preparation of SOF4 with high purity. The solid‐state structure has also been elucidated and compared with the reported gas phase one. The use of this reagent for the formation of the emerging pentafluorooxosulfate [cat][OSF5] anions led to the preparation of multiple ion‐pairs (cat=Ag, NEt3Me, PPN, PPh4) in different organic solvents. The SuFEx reservoir ability of this anion was studied and by tuning the solvent system, the reactivity of pure thionyl tetrafluoride was observed using Ag[OSF5] in THF and acetone.

Novel methodology for O-functionalization of carbohydrate derivatives has been established using benchstable and easily prepared iodonium(III) reagents.B oth electron-withdrawing and electron-donating aryl groups were introduced under ambient conditions and without precautions to exclude air or moisture.F urthermore,t he approach was extended both to full arylation of cyclodextrin, and to trifluoroethylation of carbohydrate derivatives.T his is the first general approacht oi ntroduce traditionally non-electrophilic groups into any of the OH groups around the sugar backbone.T he methodology will be useful both in synthetic organic chemistry and biochemistry,a si mportant functional groups can be incorporated under simple and robust reaction conditions in afast and efficient manner. Scheme 1. Approaches to introduce noncarbohydrate functional groups. LG = leaving group, Pg = protecting group.

Bonding in six-coordinate complexes based on Group 13 elements (B, Al, Ga, In, Tl) is usually considered to be identical to that in transition-metal analogues. We herein demonstrate through sophisticated electronic-structure analyses that the bonding in these Group 13 element complexes is fundamentally different and better characterized as electron-rich hypervalent bonding with essentially no role for the d orbitals. This characteristic is carried through to the molecular properties of the complex.

Hypervalent iodine compounds have enjoyed a very rich chemistry in recent years. Many novel reactions have been developed, and new reagents as well as strategies have expanded the repertoire of the synthetic chemist. [1] Hypervalent bromine compounds, however, have not been considered seriously although they have been known for a long time. Already in 1952 the formation of the diazonium salt from amine 1 and subsequent thermal decomposition yielding the l 3-bromane derivative 2 was described (Scheme 1). [2]

The stereoisomers of 7_acetylbenzo[b]naphtho[ 1,8-&@iazocin-8(7@-one 13-oxide (1) were studied by a semiempirical MO method (AM 1). The structure of the sulfoxide-lactam-type title compound is determined by the position of the sulfinyloxygen (equatorial/axial; E/A) and by the cis/trans configuration of both the endocyclic and exocyclic amide moieties (enC/ enT and exC/exT). The shape of the eight-membered 1,5-thiazocine ring (boat/chair/twist-chair; Bt/Ch/Tw) is controlled by the variation of configuration parameters. By using an automatic research program the expected eight energy minima were found on the potential energy hypersurface. The structure belonging to the global minimum (la) agrees well with that found experimentally by X-ray methods (Bt-E-enC-exT). Here, in the global minimum, the sulfur atom exhibits a sulfurane-like configuration with a relatively short transannular S. .N nonbonded distance (2.85 A). An analogous situation emerges by rotating the exocyclic amide moiety in the cis position (AE = 0.9 kcal mol-'). The change in the sulfur configuration (E-+ A) causes an increase in energy (AE = 3.!-9.3 kcal mol-') and the disappearance of the sulfurane-like geometry with elongation of the S... N distance (3.15-3.16 A). The cis-trans change in the endocyclic amide part is associated with a Bt-+ Ch transformation causing appreciable steric constraint and energy increase (AE = 11.5-14.1 kcal mol-'). The sulfurane geometry is somewhat distorted and the S. N distance is significantly increased (3.28-3.30 A). Simultaneous E + A and enC + enT changes both bring about a Bt + Tw transformation with a large increase in energy (AE = 7.0-22.2 kcal mol-'); the sulfurane geometry disappears and the r(S N) distance increases (3.06 A). The extremely high energy value obtained for the Tw-A-enT-exT structure is attributed both to the twist-chair ring structure and the unfavorable close contact of oxygen atoms belonging to the sulfur and endo-carbonyl-carbon atoms. The spirosulfurane isomer (3) of the title compound is computed to be more stable than la (AE =-11 kcal mol-').

Hypervalent iodine compounds have enjoyed a very rich chemistry in recent years. Many novel reactions have been developed, and new reagents as well as strategies have expanded the repertoire of the synthetic chemist. [1] Hypervalent bromine compounds, however, have not been considered seriously although they have been known for a long time. Already in 1952 the formation of the diazonium salt from amine 1 and subsequent thermal decomposition yielding the l 3-bromane derivative 2 was described (Scheme 1). [2]

Hypervalent iodine compounds have enjoyed a very rich chemistry in recent years. Many novel reactions have been developed, and new reagents as well as strategies have expanded the repertoire of the synthetic chemist. [1] Hypervalent bromine compounds, however, have not been considered seriously although they have been known for a long time. Already in 1952 the formation of the diazonium salt from amine 1 and subsequent thermal decomposition yielding the l 3-bromane derivative 2 was described (Scheme 1). [2]

Hypervalent iodine compounds have enjoyed a very rich chemistry in recent years. Many novel reactions have been developed, and new reagents as well as strategies have expanded the repertoire of the synthetic chemist. [1] Hypervalent bromine compounds, however, have not been considered seriously although they have been known for a long time. Already in 1952 the formation of the diazonium salt from amine 1 and subsequent thermal decomposition yielding the l 3-bromane derivative 2 was described (Scheme 1). [2]

The reactivity of benzyl hypervalent iodine intermediates was explored in congruence with the reductive iodonio-Claisen rearrangement (RICR) to show that there may be an underlying mechanism which expands the reasoning behind the previously known C-C bond-forming reaction. By rationalizing the hypervalent iodine's metal-like properties it was concluded that a transmetallation mechanism could be occurring with metalloid groups such as silicon and boron. Hypervalent iodine reagents such as Zefirov's reagent, cyclic iodonium reagents, iodosobenzene/BF, and PhI(OAc)/BF or triflate-based activators were tested. A desirable facet of the reported reaction is that iodine(I) is incorporated into the product thus providing greater atom economy and a valuable functional group handle for further transformations. The altering of the RICR's -selectivity to form -selective products with benzyl hypervalent iodine intermediates suggests a mechanism that involves hypervalent iodine-guided...

Using 18 silatranes XSi(OCH2 CH2 )3 N (1) as examples, the potentials of electrochemical oxidation E(0) of the hypervalent compounds of Si were calculated for the first time at the ab initio and DFT levels. The experimental peak potentials Ep (acetonitrile) show an excellent agreement (MAE=0.03) with the MP2//B3PW91 calculated E(0) (C-PCM). Radical cations of 1 reveal a stretch isomerism of the N→Si dative bond. Localization of the spin density (SD) on the substituent X and the short (s) coordination contact Si⋅⋅⋅N (dSiN <2.13 Å) along with the high five-coordinate character of Si are typical for the first isomer 1(+.(s)) , whereas the second one, 1(+.(l)) , has a longer (l) Si⋅⋅⋅N distance (dSiN >3.0 Å), the four-coordinate Si and the SD localized on the silatrane nitrogen atom Ns . The vertical model of adiabatic ionization (1→1(+.(s)) or 1→1(+.(l)) ) was developed. It allows, in accordance with an original experimental test (electrooxidation of 1 in the presence of ferrocen...

Hypervalent iodine compounds have enjoyed a very rich chemistry in recent years. Many novel reactions have been developed, and new reagents as well as strategies have expanded the repertoire of the synthetic chemist. [1] Hypervalent bromine compounds, however, have not been considered seriously although they have been known for a long time. Already in 1952 the formation of the diazonium salt from amine 1 and subsequent thermal decomposition yielding the l 3-bromane derivative 2 was described (Scheme 1). [2]

We herein report a robust catalyst-free cross-coupling between ArI(OAc)2 and α-stannyl nitriles, aided by TMSOTf. The transformation introduces a cyanoalkyl group to the ortho position of ArI(OAc)2 and simultaneously reduces the aryl iodine(III) to iodide, thus providing α-(2-iodoaryl) nitrile as the product. This transformation could be completed within 5 min at -78 °C and features superb functional group tolerance and efficient scalability. DFT calculations indicate that the formation of a ketenimine(aryl)iodonium intermediate and subsequent [3,3]-sigmatropic rearrangement are involved as key steps.

Reaction of NaIO 3 with aHF 4.2.2 The Preparation of 4-Fluoro-1-(tetrafluoroiodo)benzene 4.2.3 ligands (L = F: ca.-0.5 a.u.). [8] The filled nonbonding molecular orbital has a node at the central iodine atom. The partial positive charge on iodine in the highly polarised 3c-4e bond makes the aryl-λ 3-iodane an electrophilic agent. The inherent nature of the 3c-4e bond explains the preferred orientation of more electronegative ligands in the apical positions. For non-metals of the same group more electropositive central atoms are energetically favoured for hypervalent species: thus in general, λ 3-iodanes are more stable than analogous λ 3bromanes and λ 3-chloranes. [10, 11] Compounds of iodine(III) with one carbon ligand are represented by organic iodosyl compounds (RIO, where R is usually aryl) and their derivatives (RIX 2 , where X represents an electronegative ligand). The second iodine(III) class with two carbon ligands on iodine includes various iodonium salts (R 2 I + X-). The overwhelming majority of known, stable organic compounds of polyvalent iodine belong to these two classes. The two heteroatom ligands X attached to iodine in RIX 2 are commonly represented by fluorine, chlorine, ON N-, and strongly electronegative C-substituents. In general, only RIX 2 derivatives bearing the L L L Ar .. : A very high fugalibility (leaving group ability) of iodanyl groups (λ 1) is among the most source giving the pure (difluoroiodo)arenes. [24] For a high yield the electrochemical preparation of para-substituted (difluoroiodo)arenes Et 3 N ⋅ n HF was recently used as reagent. [25, 26] Moreover, (difluoroiodo)arenes are formed readily when the corresponding iodosyl or bis(trifluoracetoxy)iodoarenes are treated with sulfur tetrafluorid at-20 °C.

Hypervalent iodine compounds have enjoyed a very rich chemistry in recent years. Many novel reactions have been developed, and new reagents as well as strategies have expanded the repertoire of the synthetic chemist. [1] Hypervalent bromine compounds, however, have not been considered seriously although they have been known for a long time. Already in 1952 the formation of the diazonium salt from amine 1 and subsequent thermal decomposition yielding the l 3-bromane derivative 2 was described (Scheme 1). [2]

Organo-phosphorus compounds S 0080 Efficient One-Pot Synthesis of Secondary Cyclic Phosphanes with Easy Regeneration of the Phosphorus-Donor Reagent Used.-An unusual phosphane obtained by reaction of p-methylthioanisole and PCl3 and AlCl3 is used as phosphorus-donor for the reaction with a Grignard reagent followed by treatment with aqueous acid to afford secondary cyclic phosphanes. The reagent can be easily regenerated by treatment of by-product (III) with PCl 3 .-(BACCOLINI*, G.; BOGA, C.; GALEOTTI, M.;

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes. This formal C-H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α-(2-iodoaryl)ketones are versatile synthetic building blocks.

Primary phenylmethanols are selectively and efficiently oxidized to the corresponding aldehydes by the system C 6 H 5 IO=(C 6 H 5) 4 PBr=CH 2 Cl 2 , T ¼ 298 K under aerobic conditions. The use of the relatively stable iodosobenzene, an iodine(III) compound, in place of the usually employed and potentially explosive iodine(V) reagents, the easy work-up procedure, and the facile recycling of solvent and oxidant provides a convenient and environmentally benign oxidation method.

Dicationic lO-C-.5 species 14, formally two-electron oxidation products of 1,8-bis(arylthio)-9-(2,6-di-methoxyary1)-1 O-phenylanthracenes, are prepared and characterized by NMR spectroscopy. Evidence is presented for a bis-stdfonium structure containing a hypervalent trigonal bipyramidal (TBP) carbon atom. Dicationic species 14, prepared by the reaction of the appropriate diol with strong acid in liquid sulfur dioxide or sulfurylchlorofluoride, are stable for indefinite periods at room temperature in these solutions. Structural features common to these compounds which stabilize the TBP geometry sufficiently to allow their direct observation are as follows: (a) electronegative apical ligands (sulfonium sulfur atoms), (b) five-membered rings linking each apical position to an equatorial position, (c) geometric constraints built into the tridentate ligand in a pattern designed to stabilize TBP, relative to tetrahedral carbon, (d) three relatively electropositive (sigma-donor) equatorial ligands, which decrease the effective ebctronegativity of the central carbon atom of the threecenter bond, (e) a strain-free, bidentate wacceptor equatorial ligand with its waxis parallel with the electron-rich three-center four-electron bond axis, and (0 possible residual aromaticity (bis-ipso-aromaticity) in the equatorial six-membered ring incorporating the hypervalent carbon atom. A low-temperature 19F NMR study of 14b sets an upper limit for AG#-,owc of ca. 4 kcallmol for a hypothetical pr0ces.s which would interconvert unsymmetrical species 30 and 30' if such a tautomeric mixture were to represent the structure of 14. Evidence against such a tautomeric equilibrium is adduced from the upfield shift of 0.65 ppm observed for the proton meta to the two methoxyl substituents of dication 14a relative to the comparable proton in 21a, the model dication lacking one of the two arylthio substituents of 14a. This is most easily explained by postulating a nucleophilic interaction of the second thioaryl group in 14 at the hypervalent, 10-C-5 carbon.

Ab initio methods are used to investigate ring strain effects on sulfide-singlet oxygen reaction intermediates. The optimized persulfoxide and thiadioxirane structures derived from 3-, 4-, and 5-membered ring sulfides showed minor albeit systematic changes in geometry. These persulfoxides and thiadioxiranes are best described as distorted tetrahedral and trigonal bipyramidal in nature, respectively. We find that the persulfoxy sulfur becomes less sulfonium-ion-like in character with decreasing ring size. In addition, the persulfoxide and the thiadioxirane are nearly isoenergetic in all cases and their interconversion barriers are nearly identical. We speculate that the anticipated ring strain effect in the persulfoxide is compensated for by a weaker sulfur-oxygen interaction and the corresponding relaxation of the need to attain the energetically preferred tetrahedral geometry.

Iodosylbenzene (iodosobenzene, PhIO) is a known oxygen atom transfer agent with interesting bioinorganic applications (e.g., formation of high-valent iron species), and is regarded as a representative member of a class of hypervalent iodine complexes. Iodine-oxygen bonding is analyzed in this and related complexes, based on molecular orbitals and Mulliken population analyses obtained from density functional theory (DFT) calculations. All data is seen to be straightforwardly interpretable in terms of a sigma dative bond between neutral iodine and oxygen units, as opposed to any alternative explanations involving iodine d-orbitals or hypervalence at the iodine.

New triarylamine dialkylsulfonium salts that are photosensitive in the near-ultraviolet have been prepared. The quantum yields of photoacid generation were found to be ∼0.5 and are independent of the counterion. On the other hand, the efficiencies of the sulfonium salts toward the photopolymerization of cyclohexene oxide depend on the counterion and the sulfonium substituents. Photopolymerization kinetic studies demonstrate that these triphenylamine sulfonium salts are highly efficient cationic photoinitiators.

New phenyliodine(III) sulfate (PhIO) 3 ·SO 3 , which has a complex polymeric structure of the trimeric iodosylbenzene units linked by sulfate anions, can be conveniently prepared by treatment of (diacetoxy)iodobenzene with sodium bisulfate in the presence of water. This sulfate can find practical appli-[a]

The rates of hydrolysis of benzoannelated vs nonbenzoannelated sulfuranes, viz. 5 vs 3 or 5 vs 4, were compared. Benzoannelation was found to provide very modest kinetic stabilization. Crystal structures of sulfuranes 3 and 4 were obtained and compared with each other, with a dibenzoannelated sulfurane, 17, and with a non-sulfurane analogue of 4. Bond length variations could be understood in the context of simple resonance arguments. (17)O NMR studies of 3-5 showed that this technique was indeed sensitive to sulfurane structure. For example, the chemical shifts of the two carbonyl oxygens of 4 differed by over 20 ppm. Other hypervalent systems, mainly iodinanes, were studied by (17)O NMR. A variety of theoretical methods were surveyed to test how well they could reproduce the geometry of 3. Density functional theory calculation outperformed ab initio geometry optimization at the MP2/3-21G() level. Finally, a cis-trans isomerization of the double bond of 11 and one of the two double bonds of 10 was studied.

Bis(acetoxy)iodobenzene and related acyloxy derivatives of hypervalent I(III) were studied by variable temperature solution-state 17 O-NMR and DFT calculations. The 17 O-NMR spectra reveal a dynamic process that interchanges the oxygen atoms of the acyloxy groups. For the first time, coalescence events could be detected for such compounds, allowing the determination of activation free energy data which are found to range between 44 and 47 kJ/mol. The analysis of the 17 O linewidth measured for bis(acetoxy)iodobenzene indicates that the activation entropy is negligible. DFT calculations show that the oxygen atom exchange arises as a consequence of the [1,3]-sigmatropic shift of iodine. The calculated activation barriers are in excellent agreement with the experimental results. Both the 17 O-NMR and DFT studies show that the solvent and chemical alterations, such as modification of the acyl groups or para-substitution of the benzene ring, hardly affect the energetics of the dynamic process. The low I-O Wiberg bond index (0.41-0.42) indicates a possible explanation of the invariance of both the energy barrier and the 17 O chemical shift with para-substitution.