Types Of Ylides Research Articles

Cyclic‐Phenoxaphosphinine‐Based Mixed Phosphonium‐Iodonium Ylides with Electron‐Withdrawing Substituents – Synthesis and Structural Features

AbstractA series of phosphonium ylides and mixed phosphonium‐iodonium ylides based on cyclic phenoxaphosphinine has been synthesized, representing a new structural type of ylides. The influence of the electron‐withdrawing substituents of various nature on the stability and physicochemical properties of phenoxaphosphonium ylides is discussed. Our findings reveal a progressive reduction in ylide stability as the carbonyl group is replaced first with a phosphonate group and then with a nitrile group. NMR data indicates that the presence of a cyclic phosphonium group results in a lowered energy barrier to rotation about the carbon‐carbon bond, both in phosphonium and mixed phosphonium‐iodonium ylides with α‐carboxyl substituents when compared to triarylphosphonium ylides. These experimental results are further supported and analyzed in the context of density functional theory (DFT) calculations.

Detection of Ylide Formation between an Alkylidenecarbene and Acetonitrile by Femtosecond Transient Absorption Spectroscopy.

Femtosecond laser flash photolysis of 3-(1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-ylidene)tetrahydrofuran produces singlet 3-oxacyclopentylidenecarbene which reacts with acetonitrile solvent to form an ylide. This is the first direct detection of ylide formation by an alkylidenecarbene. This new type of ylide was observed to have a broad absorption band in the visible region with λmax ∼450 nm and a lifetime of ∼13.5 ps. As with other "conventional" carbenes (the divalent carbon atom is separately bound to two substituents), this ylide formation method could be also useful for detecting alkylidenecarbenes, especially those that do not absorb at wavelengths suitable for direct observation. Furthermore, the mechanisms by which 3-oxacyclopentylidenecarbene forms the ylide and the overall favorability of ylide formation, vis-à-vis ring expansion of the carbene to strained 3-oxacyclohexyne, were supported by results from density functional theory calculations.

Rhodium-Catalyzed Geminal Oxyfluorination and Oxytrifluoro-Methylation of Diazocarbonyl Compounds.

A new reaction for the rhodium‐catalyzed geminal‐difunctionalization‐based fluorination is presented. The substrates are aromatic and aliphatic diazocarbonyl compounds. As the fluorine source a stable and easily accessible benziodoxole reagent was used. A variety of alcohol, phenol, and carboxylic acid reagents were employed to introduce the second functionality. The reaction was extended to trifluoromethylation using a benziodoxolon reagent. The fluorination and trifluoromethylation reactions probably proceed by a rhodium‐containing onium ylide type intermediate, which is trapped by either the F or CF3 electrophiles.

Rhodium‐Catalyzed Geminal Oxyfluorination and Oxytrifluoro‐Methylation of Diazocarbonyl Compounds

AbstractA new reaction for the rhodium‐catalyzed geminal‐difunctionalization‐based fluorination is presented. The substrates are aromatic and aliphatic diazocarbonyl compounds. As the fluorine source a stable and easily accessible benziodoxole reagent was used. A variety of alcohol, phenol, and carboxylic acid reagents were employed to introduce the second functionality. The reaction was extended to trifluoromethylation using a benziodoxolon reagent. The fluorination and trifluoromethylation reactions probably proceed by a rhodium‐containing onium ylide type intermediate, which is trapped by either the F or CF3 electrophiles.

Theoretical Elucidation of the Mechanism of the Cycloaddition between Nitrone Ylides and Electron-Deficient Alkenes

A full theoretical study of the reaction between a novel type of ylide, i.e. nitrone ylides, and alkenes has been carried out. Both concerted and polar stepwise mechanisms have been considered. Only the zwitterionic mechanism predicts correctly the experimentally observed adducts. Depending on the level of theory, the mechanism moves from concerted to polar stepwise, as demonstrated by the corresponding IRC analyses. The regio- and stereoselectivity of the reaction is well explained for both mono- and disubstituted alkenes. In the case of methyl acrylate a pathway leading to the two diastereoisomers obtained experimentally is predicted. For methyl fumarate a stereospecific mechanism is predicted as a consequence of a C-H···O═C interaction present in a Li-tricoordinated transition structure. The stereospecificity in the reaction with methyl maleate comes from a less hindered coordination around the lithium atom. Calculations with B3LYP and M06-2X functionals indicate that only the latter provides energy values in good agreement with experimental findings.

Hydrogen-shift isomers of ionic and neutral hydroxypyridines: a combined experimental and computational investigation

Apart from pyridine N-oxide ( 1a), the C 5H 5NO family of stable molecules comprises, 2-, 3- and 4-hydroxypyridine ( 2a, 3a and 4a) as well as their keto counterparts 2-, 3- and 4(1 H)-pyridone ( 2b, 3b and 4b). This study focuses on the characterisation of their radical cations and a number of stable H-shift isomers, which are α- or β-distonic ions. This was done by using a combination of mass spectrometric experiments and computational chemistry, at the B3LYP/CBSB7 level of theory. The ionic species were identified on the basis of both their collision-induced dissociation (CID) characteristics and specific associative ion–molecule reactions with dimethyl disulfide and tert-butyl isocyanide as substrates. The distonic ions ( 1b +, 2c +, 2d + and 3c +) were obtained by dissociative electron impact ionisation and subjected to neutralisation–reionisation mass spectrometry (NRMS). From CID spectra of the intense survivor ions, it follows that the neutral counterparts of the α-distonic ions 2c + and 3c + are viable chemical species in the rarefied gas phase. The energy-rich ylide type neutrals 1b, on the other hand, readily isomerise into pyridine N-oxide, 1a, or else dissociate. The neutral counterpart of the β-distonic ion 2d + only has a marginal stability and part of these neutrals are proposed to isomerise into energy-rich 2-pyridone molecules 2b. This is in agreement with the computational results. However, ionised 2-pyridone cannot readily be differentiated from its enol isomer 2-hydroxypyridine. In contrast, the keto isomers of ionised 3- and 4-hydroxypyridine display characteristically different CID spectra.

Additions of stabilised and semi-stabilised sulfur ylides to tosyl protected imines: are they under kinetic or thermodynamic control?

Sulfur ylides react with imines, via betaines, to give aziridines. We sought to determine whether betaine formation was reversible in reactions of benzyl-, amide- and ester-stabilised ylides by carrying out cross-over experiments. Thus, the intermediate betaines were generated independently from the corresponding sulfonium salt in the presence of a more reactive imine (p-nitrobenzaldimine). It was found that no incorporation of the more reactive imine was observed in reactions with the benzyl-stabilised ylide, whilst >80% incorporation of the p-nitrobenzaldimine was observed from the ester- and amide-stabilised ylides. These results indicate that benzyl-stabilised ylides react irreversibly with imines but ester- and amide-stabilised react reversibly. Thus, the stereocontrolling step of the process is dependent on the type of ylide employed and the results are used to account for the different diastereoselectivities observed with the different ylides.

Syntheses and Theoretical and Mechanistic Aspects of 1-Thia-2,4- and 1-Thia-3,4-diphosphole Formed from CS2 and tBuCP and Crystal and Molecular Structure of the First 1-Thia-3,4-diphosphole Complex: cis-[{PtCl2(PEt3)}2(P2SC2tBu2)

The reaction of tBuCP with CS2 (or its ylide type complexes such as R3PCS2 (R = Et, Ph, cyclohexyl), (C5H10N)2CCS2, or (C4H8NO)2CCS2) gives a mixture of 3,5-di-tert-butyl-1-thia-2,4-diphosphole and 2,5-di-tert-butyl-1-thia-3,4-diphosphole, which were characterized by NMR spectroscopy. The latter was also characterized by the single-crystal X-ray structure determination of its bis(platinum(II)) complex [(PtCl2PEt3)2(μ-P2SC2tBu2)]. This is the first structural characterization of a 1-thia-3,4-diphosphole ring. The mechanism of these reactions was explored by B3LYP/6-311+G** level quantum chemical calculations. The reaction pathway involves a phosphadithiolediylcarbene and its diphosphatetrathiafulvalene dimer as intermediates. Several other possible reaction pathways were ruled out.

エーテル型オキソニウムイリド形成を仮説とする合成反応

Ethereal oxonium ylides are highly reactive and short-lived intermediates compared with other onium ylides. While they possess appreciable potential for synthetic use, e.g. in substituting one of the two ethereal ligands for a carbene-derived group, systematic use of this type of ylides for synthesis has been limited. Recently, we have found novel methods of controlling the reactivity of the ylides on the basis of designing intramolecular ketocarbenoid or carbene reactions with cyclic ethereal moieties. The findings are (1) use of protic nucleophiles for trapping the ylides in the form of oxonium ions to suppress both undesired side-reactions and dissociation to carbenes. Thus, with cyclic ethers, acetals and orthoesters, ring-enlargement reactions take place predominantly over sigmatropic pathways of oxonium ylides, thus enabling the synthesis of macrocycles bearing ketopolyether functionality. (2) Strained bicyclo [3.n.O] oxonium ylides derived from cyclic ethers undergo sigmatropic ring-cleavage reaction to give alkenyloxyketenes efficiently. (3) Silyl reagents can trap the ylides to form ring-enlarged enol silyl ethers, which are versatile intermediates for both the ring-enlargement and novel C-C bond formation reactions with carbon electrophiles. (4) Not only ketocarbenoids but also free alkylidenecarbenes bearing a cyclic ether or acetal group undergo the similar ring-enlargement. Similar reaction of sulfonium analogues is also described.

The reaction of cyclopentadienylidine, fluorenylidene and tetrachlorocyclopentadienylidene with alcohols. A laser flash photolysis study

Rate constants of reaction of cyclopentadienylidene, fluorenylidene and tetrachlorocyclopentadienylidene with alcohols and other quenchers were determined by laser flash photolysis methods. The rate constants of reaction of cyclopentadienylidene and fluorenylidene with various alcohols were determined and found to increase with increasing alcohol acidity. Alcohols as a group reacted faster with cyclopentadienylidene and fluorenylidene than likely ylide formers such as pyridine, ethyl acetate and tetrahydrofuran. Bronsted plots of the reaction of cyclopentadienylidene and fluorenylidene with alcohols are linear with slopes of 0·061 and 0·082, respectively. In the case of tetrachlorocyclopentadienylidene, an ylide type of reaction mechanism with alcohols is indicated. Tetrachlorocyclopentadienylidene reacts most rapidly with the least acidic alcohol studied and this carbene reacts more rapidly with tetramethylurea, pyridine and tetrahydrofuran than with methanol.

Cyclic Delocalization Effects in Substituted λ5-Diaza- and Triazaphosphorines

Abstract Six-membered cyclophosphaeenes, I,3-diaza-and I,3,5-triaza-2-phosphorines are characterized by a dipolar structure of ylide type with & positive charge on phosphorus atom and negative one, delokalized in an azine fragment. In n-donor substituents at a phosphorus atom as well as in electron-acceptor substituents in 4,b heterocycle position this leads to an anomalous ratio of length of formally ordinary exo-cyclic and double endocyclic bonds PNexo > PNendo. Quantum chemical analysis of the situation performed by means of SCF method in CND0/2 approximation reveals more pronounced s-character of nitrogen atoms in exocyclic bonds in comparison to endocycli ones.

Intramolecular Cycloaddition of the Azomethine Ylides Derived from α-Amino Acids or Esters and 5-Oxo-6-heptenals or 4-Oxo-5-hexenals

Abstract Intramolecular cycloadditions of the azomethine ylides bearing a carbonyl-activated olefinic moiety, generated from α-amino acids or esters and 5-oxo-6-heptenals or 4-oxo-5-hexenals, produce the stereoselective internal cycloadducts either to olefin or carbonyl dipolarophilic function with normal or inverse regioselectivity, depending upon the types of ylides as well as the intervening chain length. Exclusively high diastereofacial selectivity has been achieved when 2-phenyl-4-thiazolidinecarboxylic acid and its methyl ester are utilized.

Chemische und spektroskopische untersuschungen an komplex-kationen des types [C 5H 5Fe(CO) 2(R 3EX)] +. Ein beitrag zur diskussion der koordinationseigenschaften von phosphanchalkogeniden und deren höheren homologen

The cations [C 5H 5Fe(CO) 2(R 3EX)] + are prepared from [C 5H 2Fe(CO) 2THF] + and R 3EX (R  CH 3, i-C 3H 7, t-C 4H 9, C 6H 5, N(CH 3) 2; E  P, As, Sb; X  S, Se). NMR data indicate the ligands to be strong donors of the ylide type R 3E +-X − in the coordinated state. On the other hand, the relative donor strength E  P > Sb > As may be interpreted as a result of (X → E) π bonding.

Syntheses and Some Properties of N-Alkyldimethylaminealkanesulfonimides

N- Trimethylaminealkanesulfonimides (1-R-S) and N-alkyl-dimethylaminemethanesulfonimides (R-1-S), R : n-C12H25 and n-C16H33, were derived from 1, 1-dimethyl- or 1-alkyl-1-methyl-hydrazine. Their properties were compared with those of the corresponding amineimides, (1-R) and (R-2).On NMR spectra of the ylides, the chemical shift for methyl or methylene groups adjacent to the positive nitrogen was 3.4ppm relative to TMS. For amineimides, it was 3.203.29ppm. On IR spectra, S-O frequencies of the aminesulfonimides were lowered by 60100cm-1 in comparison with those of the corresponding hydrazines or hydrazinium salts. This frequency fall is probably due to a delocalization of the negative charge on the nitrogen, similar to that operating in amineimides. But the degree of this fall was larger than that for amineimides.The aqueous solution was neutral and showed a low electric conductivity, analogous to those of amineimides. The comparison of their properties among the four types of ylides having the same alkyl groups gave the following results : mp, 1-R-S>R-1-S>1-R>R-2; Krafft point, R-1-S>1-R-S>1-R>R-2; cmc, 1-R-S<R-1-S<R-2<1-R; surface tension above cmc, R-1-S<1-R-S<1-R<R-2. Foaming and penetrating powers were also measured.

Reaction of N-Aminopyridinium Derivatives. III. Synthesis of s-Triazolo [1, 5-α]-pyridine Ring.

N-Aminopyridinium salt (I) was reacted with cyanide ion in water at room temperature to give 2-(4-pyridyl)-s-triazolo [1, 5-α] pyridine (IV). In alkaline medium I exists as an equilibrium mixture with the ylide type, N-iminopyridine (II) which was reacted with several nitrile compounds to produce s-triazolo [1, 5-α] pyridine derivatives by 1, 3 dipolarcyclo addition. This novel triazole ring could also be synthesized by ring closure of 1, 2-diaminopyridinium salt with a carboxylic acid, acid chloride or acid anhydride. Reaction of N-methylaminopyridinium salt (XIII) or N-acetamidopyridinium salt (XIV) with cyanide ion did not afford any 1, 3-dipolar cycloaddition products. Explanation for the difference in reactivity among I, XIII and XIV was attempted from each pKa' values.