The crystal and molecular structure of pentafluoropropionylbenzoylmethylene triphenylphosphorane

The crystals of pentafluoropropionylbenzoylmethylene triphenylphosphorane that bears two strongly electron-withdrawing groups in alkylidene moiety are monoclinic and its space group is C2/c, with a = 11.271(3)Å, b = 18.253(6)Å, c =23.938(7)Å, β = 91.09(2)°, z = 8. The X-ray diffraction intensity data were collected on a four-circle diffractometer. The structure has been solved by direct method and refined by block-diagonal least-squares method. The final R- index was 0.075 for 3146 independent observed reflexions. In this paper the structure of this ylide is compared with that of corresponding arsonium ylide previously reported. Both ylidic skeleton structures are planar with sp² hybridization. The bond length of P-C(1) is 1.748 (5)Å with bond order. 1.60 while the bond order of As-C(1) in the corresponding arsonium ylide is 1.46, indicating that the phosphonium ylide has a greater contribution of “ylene” structure to the overall structure. As a result the phosphonium ylide should be less reactive than the corresponding arsonium ylide. In both ylides, (he major delocalized canonical forms of negative charge are shown to be 3.     

Reactivity of aldehydes with semi-stabilised arsonium ylide anions: synthesis of terminal (e)-1,3-dienes

A study of the reactivity of semi-stabilised arsonium ylide anions in olefination reactions is presented. The different ylide anions were generated by the addition of nBuLi to various arsonium halide derivatives: [Ph(2)As(R)R'](+)X(-), where R and R' are methyl, allyl, prenyl or benzyl groups. By using diallyldiphenylarsonium bromide (R=R'=allyl) an olefination protocol was optimised allowing the efficient transformation of aliphatic aldehydes into terminal 1,3-dienes with a high selectivity for the E isomer (E/Z ratios ranging from 90:10 to 97:3). The olefination reactions of aldehydes with dissymmetric arsonium halides (R not equal R') are very chemoselective; with arsonium ylide anions the benzyl moiety is more reactive than the allyl moiety which is much more reactive than prenyl and methyl groups. Based on the experimental results, a mechanism is proposed for the reaction.     

氮叶立德高立体选择性地合成螺[环丙烷-1,4'-吡唑啉-5'-酮] 衍生物的研究

螺环丙基杂环化合物是一类具有重要药理、生理活性的化合物, 研究和发展这类化合物的新的立体选择性合成方法是当前有机合成领域的一个热点. 对1,4-二氮杂双环[2.2.2]辛环(DABCO)衍生的氮叶立德与3-甲基-1-苯基-4-芳亚甲基-5-吡唑啉酮合成螺环丙基吡唑啉酮的反应做了研究, 并与胂叶立德所参与的类似反应的结果做了比较, 发现仅得到单一反式结构产物, 但存在exo和endo两种构型, 其中前者为主要产物. 产物结构由IR, MS, 1H NMR, 13C NMR, 元素分析和X射线衍射鉴定. 还从反应机理角度对两种叶立德性质对反应的影响做了解释.     

Synthesis of stable arsonium and sulfur ylides from perfluoroalkanesulfonyl diazocarbonyl compounds and their X-ray diffraction analysis

A series of stable fluorine-containing arsonium ylides and sulfur ylides were simply synthesized from perfluoroalkanesulfonyl diazocarbonyl compounds in the presence of rhodium catalyst. The ylide products are fairly stable due to the strong electron-withdrawing properties of perfluoroalkanesulfonyl group and carbonyl group. They are fully confirmed by spectral methods and the structures of 3ba and 3cd are also established by X-ray single crystal diffraction analysis. Several interesting features about the ylide structures and some weak fluorine interaction between them are described here.     

Tributylarsonium-2,2,3,3,4,4-hexafluorocyclobutane ylide. Preparation and cleavage

$\text{F}$-cyclobutene forms a stable ylide with $\text{n}$-tributylarsine. In contrast to the halogen cleavage of the analogous phosphonium ylide, which gives 1,1-dihaloalkanes, the arsonium ylide reacts with bromine and iodine to give the 1-halo-$\text{F}$-cyclobutenes.     

Keto-stabilized Arsenic Ylides and their Coordination to Gold(I)

Three different arsonium salts were prepared by a solvent-free method from Ph₃As and the respective 2-bromoacetophenones. These salts were deprotonated by NaOH to form keto-stabilized arsenic ylides. The ylids react with [AuCl(tht)] affording gold(I) complexes containing the C-bound ylide. The compounds were characterized by NMR spectroscopy, IR spectroscopy, and X-ray diffraction.     

A study of influence of temperature and <Emphasis Type="Italic">N</Emphasis>, <Emphasis Type="Italic">N</Emphasis>-acyl protected keto ylides structure on their predominant transformations

The effect of temperature and keto ylides structure on preference of their intramolecular cyclization leading to N-containing heterocyclic compounds or linear products formation has been investigated at the B3LYP/6-31G(d,p) level of theory. It has been determined that the thermodynamic advantage of the cyclization reactions of ylides increases with temperature, while Gibbs free energies of linear products formation reactions depend insignificantly on temperature. The Wittig and the Corey–Chaykovsky reactions are least probable in the case of the sulfonium and ammonium ylides considered. However, for phosphonium ylides the Wittig reaction must be considerably preferable in comparison with other routes, while behavior of the arsonium ylides is predicted to be more complex. Research of S-ylides transformations shows that formation of methylthio-substituted heterocycles with five-, six- or seven- membered rings is possible from a thermodynamic standpoint, while conversion of the corresponding ylide to a four-membered heterocycle is disadvantageous. Presence of a methyl substituent and its position in the ylide carbon chain depends ambiguously on the behavior of sulfur keto ylides.     

A New Synthesis of Vinyl Halides via α-Halo Substituted Semistabilized Arsonium Ylide

As the first example 4 of the Wittig reaction of α-halo substituted semistabilized arsonium ylide, we utilized this reaction to synthesize vinyl iodides 5.     

The first example of α-organoseleno arsonium ylides and its Wittig-type reaction

α-Organoseleno arsonium ylide 3 was synthesized for the first time by a phenylselenenylation-transylidation reaction. It has sufficient activity to carry out the Wittig-type reaction, affording a novel method for the stereoselective synthesis of (Z)-α-phenyl-seleno-α, β-unsaturated esters 6.     

Copper‐Catalyzed Enantio‐, Diastereo‐, and Regioselective [2,3]‐Rearrangements of Iodonium Ylides

The first highly enantioselective, diastereoselective, and regioselective [2,3]‐rearrangement of iodonium ylides has been developed as a general solution to catalytic onium ylide rearrangements. In the presence of a chiral copper catalyst, substituted allylic iodides couple with α‐diazoesters to generate metal‐coordinated iodonium ylides, which undergo [2,3]‐rearrangements with high selectivities (up to >95:5 r.r., up to >95:5 d.r., and up to 97 % ee ). The enantioenriched iodoester products can be converted stereospecifically into a variety of onium ylide rearrangement products, as well as compounds that are not accessible by classical onium ylide rearrangements.     

Mass spectrometric studies of platinum(II) complexes of carbonyl-stabilized arsonium ylides

A fast atom bombardment (FAB) mass spectrometric study was carried out on the two O-coordinated carbonyl-stabilized arsonium ylide Pt(II) complexes {(dppe)PtCI[OC(R)C(H)AsPh₃]}BF₄ ((dppe) = Ph₂PCH₂CH₂Ph₂; R = CH₃ (1), OCH₃ (3)) and on the two corresponding C-coordinated isomers {(dppe)PtCl[Ph₃AsC(H)COR]}BF₄ (R = CH₃ (2), OCH₃ (4)). The mass spectral analysis of complexes 1 and 2 reveals that it is possible to distinguish the two isomeric forms mainly on the basis of the relative abundance of the protonated triphenylarsine oxide at m/z 323 while the different coordination modes of the ylide in complexes 3 and 4 are evidenced by the different fragmentation pathways of these two derivative;. Further, the reaction between [(dppe)PtCl]₂(BF₄)₂ and the appropriate ylide performed under FAB conditions indicates that in both cases the first complex formed is the C-coordinated isomer, in agreement with that observed in the condensed phase.     

One-pot synthesis of novel photochromic oxazine compounds

A one-pot domino synthesis of photochromic 2,2-diarylphenanthro-(9,10)-[2H]-[1,4]-oxazines in excellent yield is described starting with acrylic acid derivatives. The reaction mechanism was studied by ReactIR and UV-vis. The cascade sequence of the reactions involves five transformations, namely, acyl azide formation, Curtius rearrangement, arsonium ylide formation, aza-Wittig, and final cyclization to the title compounds.     

Photochemical reactions. 147th Communication. Further investigation of the photochemistry of 5,6-epoxy-5,6-dihydro-β-ionone: Product formation via a carbonyl-ylide intermediate

On π,π*-excitation of the epoxyenone (E)- 1 (λ = 254 nm, MeCN), in addition to the previously isolated compounds 2 – 9 , the new products 10 – 12 , derived from the ylide intermediate c were isolated. Further evidence for the ylide c was obtained by the rapid racemization of the optically active epoxyenone (?)-(E)- 1 .     

A Direct Route to C-Vinylaziridines: Reaction of N-Sufonylimines with Allylic Ylides under Phase-Transfer Conditions or with Preformed Ylides at Low Temperature

Allylic sulfonium salts 3, 5, 7, 11, 12, 13, and arsonium salt 14 react with aromatic, heteroaromatic, and alpha,beta-unsaturated N-sulfonylimines under solid-liquid phase-transfer conditions in the presence of KOH at room temperature to produce, respectively, vinyl-, (beta-phenylvinyl)-, and [beta-(trimethylsilyl)vinyl]aziridines in excellent yields within several minutes. In some cases, pyrroline compound 9 is obtained as a minor product. This aziridination reaction has also been carried out with preformed ylides, generated from sulfonium salts 3, 7, arsonium salt 14, and telluronium salts 15, 16 with a base in THF at -78 degrees C. In most examples, quantitative yields were achieved. However, the trans/cis selectivity of the reaction was not high in either case. A semistable allylic sulfonium ylide, i.e., dimethylsulfonium 3-(trimethylsilyl)allylide, was found to not undergo an expected [2,3]-sigma-rearrangement and so can also be used in this reaction.     

The Chemistry of Vicinal Tricarbonyls: Total Syntheses of Elastase Inhibitors YM‐47141 and YM‐47142

We have completed the total syntheses of elastase inhibitors YM‐47141 and YM‐47142, the first natural products containing a vicinal tricarbonyl group. The work establishes the configuration at C(4) of the macrocyclic depsipeptide and demonstrates the generality of the phosphoranylidene‐ylide activation and protection methodology employed earlier in syntheses of α‐keto amides. Key steps involve the coupling of a carboxylic acid with a phosphorane to form a stable ylide intermediate, which contains the highly electrophilic carbonyl group in protected form. The tricarbonyl unit was unmasked at the final stage of the synthesis by oxidative cleavage of the C=P bond.     

Selenophen‐2‐yl‐Substituted Thiocarbonyl Ylides – at the Borderline of Dipolar and Biradical Reactivity

The reactions of aryl (selenophen‐2‐yl) thioketones with CH₂N₂ occur with spontaneous elimination of N₂, even at low temperature (?65°), to give regioselectively sterically crowded 4,4,5,5‐tetrasubstituted 1,3‐dithiolanes and/or a novel type of twelve‐membered dithia‐diselena heterocycles as dimers of the transient thiocarbonyl S‐methanides. The ratio of these products depends on the type of substituent located at C(4) of the phenyl ring. Whereas the formation of the 1,3‐dithiolanes corresponds to a [3+2] cycloaddition of an intermediate thiocarbonyl ylide with the starting thioketone, the twelve‐memberd ring has to be formed via dimerization of the ‘thiocarbonyl ylide’ with an extended biradical structure.     

1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Schiff Bases and Difluorocarbene to Symmetric Olefins

Difluoro(iminio)methanides generated by the action of difluorocarbene on Schiff bases react with derivatives of maleic and fumaric acids, following the 1,3-dipolar cycloaddition pattern to give 2,2-difluoropyrrolidines which were detected by gas chromatography-mass spectrometry. The final products are stereo-isomeric substituted 2-pyrrolidinones formed by hydrolysis of difluoropyrrolidines and their dehydrofluorination products, 2-fluoro-4,5-dihydropyrroles. The observed stereoselectivity of the cycloaddition suggests Z configuration of intermediate ylide and both endo- and exo-approach to the dipolarophile in the transition state corresponding to cycloaddition.     

Diastereoselective and Enantioselective Synthesis of Multi-Functionalized Isoxazoline-N-Oxides through Asymmetric [4+1] Annulations

A diastereoselective and enantioselective formal [4+1] ylide annulation of chiral sulfonium salts with various substituted Morita-Baylis-Hillman (MBH) adducts leading to optically active isoxazoline N-oxides with three chiral carbon centers has been explored. The salient features of this methodology include a high diastereo- and enantioselective transformation, easily accessible starting materials, and mild reaction conditions. In addition, the isoxazoline N-oxides products can be conveniently transformed into functionalized compounds.     

Theoretical Study of the Cycloaddition Reaction of a Tungsten‐Containing Carbonyl Ylide

The [3+2] cycloaddition reaction of a tungsten‐containing carbonyl ylide with methyl vinyl ether and the insertion reactions of the nonstabilized carbene complex intermediates produced have been investigated through the use of B3LYP density functional theory. The [3+2] cycloaddition reaction of the tungsten‐containing carbonyl ylide has been proven to proceed concertedly, reversibly, and with high endo selectivity. The intermolecular Si? H insertion reactions of the carbene complex intermediates have been proven to be favored over the intramolecular C? H insertion, in good agreement with experimental results. Moreover, the kinetic endo/exo ratio of the [3+2] cycloaddition reaction has been shown to determine the endo/exo selectivity of the Si? H insertion products. In addition, secondary orbital interactions involving the benzene ring and the carbonyl ligand on the metal center have turned out to strongly influence the high endo selectivity of the [3+2] cycloaddition reaction with methyl vinyl ether.     

A straight synthesis of 2–(α-substituted N-tosylaminomethyl)-2,5-dihydrofurans by the reaction of N-sulfonylimines with arsonium 4-hydroxyl- cis -2-butenylides

On treatment of N-tosylimines (1) and 4-hydeoxyl- cis-butenyl arsonium salt (5) with KOH in acetonitrile at room temperature, 2–(α-substituted N-tosylaminomethyl)-2, 5-dihydrofurans (4) were obtained in moderate yields. The arsonium salt (5) acts formally as an equivalent of 2,5-dihydrofuran synon. A plausible mechanism was proposed for this new 5-membered cyclization reaction.