The Mechanism of Phosphonium Ylide Alcoholysis and Hydrolysis: Concerted Addition of the O−H Bond Across the P=C Bond

The previous work on the hydrolysis and alcoholysis reactions of phosphonium ylides is summarized and reviewed in the context of their currently accepted mechanisms. Several experimental facts relating to ylide hydrolysis and to salt and ylide alcoholysis are shown to conflict with those mechanisms. In particular, we demonstrate that the pK_a values of water and alcohols are too high in organic media to bring about protonation of ylide. Therefore, we propose concerted addition of the water or alcohol O?H bond across the ylide P=C bond. In support of this, we provide NMR spectroscopic evidence for equilibrium between ylide and aclohol that does not require the involvement of phosphonium hydroxide. We report the first P‐alkoxyphosphorane to be characterised by NMR spectroscopy that does not undergo exchange on an NMR timescale. Two‐dimensional NMR spectroscopic techniques have been applied to the characterisation to P‐alkoxyphosphoranes for the first time.     

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.     

磷叶立德CH2PH3和类磷叶立德自由基∙CHPH3优势构型和C—P键结构的研究

采用MP4/6-311++G(d,p)和B3LYP/6-311++G(d,p)对磷叶立德CH₂PH₃和类磷叶立德自由基∙CHPH₃进行构型优化，从电子密度拓扑分析的角度对C—P键的键结构进行了探讨。得到如下结论：类磷叶立德自由基和磷叶立德的C—P键性质类似，但磷叶立德中π键由两个电子形成，类磷叶立德自由基中π键由一个电子形成，所以前者的π性明显，而后者的π性不明显。类磷叶立德自由基中的这个单电子在碳原子附近，垂直于对称面的方向上运动，有p_(C→P)配键的特征，所以类磷叶立德自由基∙CHPH₃中的C—P键比相应的产物∙CH₂PH₂中的C—P键要弱一些。     

Kinetics of the 1,5-dipolar cyclization of 2-Vinylpyridinium ylides to Indolizines. Determination of rate parameters by laser flash photolysis

Nanosecond laser flash photolysis (λ = 355 nm) of an aqueous solution of 3-chloro-3-p-chlorophenyldiazirine in isooctane produces a transient absorption at 310 nm due to the formation of the carbene. In the presence of 2-vinylpyridine, a second transient with a broad absorption band peaking at 520 nm grows in. This absorption is attributed to 2-vinylpyridinium ylide. The ylide decays with a lifetime equal to 33 µs at 25°C independent of the concentration of 2-vinylpyridine. As the ylide decays, there is a concomitant growth of an absorption at 330 nm, attributed to the formation of inodolizine. The activation parameters for the 1,5-dipolar cyclization of the ylide to indolizine were determined; E_a = 12.1 kcal mol^?1 and log A = 13.4. © 1994 John Wiley & Sons, Inc.     

Reactions on a 1,2-Dicarbonyl Moiety of a Fullerene Skeleton

A 1,2-dicarbonyl moiety on a cage-opened fullerene skeleton is one of suitable building blocks for the further derivatization. Herein, we discuss the chemical transformation of a 1,2-dicarbonyl compound into β-oxo-phosphorus ylide, acid anhydride, and α-methylene carbonyl derivatives. Despite possessing a sterically small methylene unit in the last one, the release of an encapsulated water molecule was significantly supressed whereas the β-oxo-phosphorus ylide bearing three bulky p-tolyl groups on the P-atom enabled the faster insertion/release dynamics, implying the flexibility of the phosphonium substituent. The replacement of the carbonyl group with phosphorus ylide and methylene units largely varied electrochemical properties of the fullerene skeleton, likely arising from the anionic charge delocalized over the entire molecule and removal of an electron-withdrawable carbonyl group, respectively.     

DFT investigation on mechanism of dirhodium tetracarboxylate-catalyzed O-H insertion of diazo compounds with H2O

The mechanism of the dirhodium tetracarboxylate-catalyzed O-H insertion reaction of diazomethane and methyl diazoacetate with H₂O has been studied in detail using DFT calculations. The rhodium catalyst and a diazo compound couple to form a rhodiumcarbene complex. Of two reaction pathways of the Rh(II)-carbene complex with H₂O, the stepwise pathway is more preferable than the concerted one. Formation of a Rh(II) complex-associated oxonium ylide is an exothermal process, and direct decomposition of the ylide gives a very high barrier. The high barriers for the 1,2-H shift of Rh(II) complex-associated oxonium ylides make the ylides become stable intermediates in both reactions, especially for the reactions in solution. Difficulty in formation of a free oxonium ylide supports experimental results, indicating that the Rh(II) complex-catalyzed nucleophilic addition of a diazo compound proceeds via a Rh(II) complex-associated oxonium ylide rather than via a free oxonium ylide.     

THE PREPARATION OF TWO NOVEL HOMOALLYLIC ALCOHOLS VIA THE REACTION OF EPOXIDE WITH PHOSPHONIUM YLIDE

Abstract

Two novel homoallylic alcohols, E-4-(4-methoxyphenyl)- 1-phenyl-3-buten-1-01 and E-4-(3,4,5-trimethoxyphenyl)-1-phenyl-3-buten-1-01, were synthesised by the reaction of methelentriphenylphosphonium ylide with epoxide. The reaction first gave an initial betaine which upon treatment with butyl lithium gave a new ylide. When this new ylide reacted with the proper aldehyde, gave the corresponding homoallylic alcohol. Preliminary biological screening showed that the former alcohol possesses a significant estrogenic activity in rats. The latter alcohol was found to have partial antiestrogenic activity.     

Cyclic (Amino)(Phosphonium Bora‐Ylide)Silanone: A Remarkable Room‐Temperature‐Persistent Silanone

A silanone substituted by bulky amino and phosphonium bora‐ylide substituents has been isolated in crystalline form. Thanks to the exceptionally strong electron‐donating phosphonium bora‐ylide substituent, the lifetime at room temperature of the silanone is dramatically extended (t _1/2=4 days) compared to the related (amino)(phosphonium ylide)silanone VI (t _1/2=5 h), allowing easier manipulation and its use as precursor of new valuable silicon compounds. The interaction of silanone with a weak Lewis acid such as MgBr₂ increases further its stability (no degradation after 3 weeks at room temperature).     

Studies on ylides: Carbonyl olefination with (p-nitro benzylidene)triphenylarsenane

(p-Nitrobenzylidene)triphenylarsenane, a semistabilized arsonium ylide has been prepared and reacted with carbonyl compounds to yield olefins as opposed to epoxidation products. Treatment of the ylide with a ranged acyl halides gave new disubstituted arsonium ylides. IR and NMR spectral data for the resulting products are reported.     

Dynamic stability of silacarbonyl ylide

The structure of silacarbonyl ylide in the singlet gound state is obtained by ab initio quantum chemical calculations. This proves the recent experimental observation of silacarbonyl ylide by the photolysis of oxasilitane [W. Ando, K. Hagiwara, and A. Sekiguchi, Organometallics 6, 2270 (1987)]. The dynamic stability of the silacarbonyl ylide is studied by the TCSCF /3-21G ^(*) method. The second-order Jahn-Teller effect is examined in connection with the active role of frontier orbitals. Configuration analysis is used to clarify characteristic electronic structure of the silylene-carbonyl interaction.     

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 .     

Phosphane‐Catalyzed [4+1] Annulation between Nitroalkenes and Morita–Baylis–Hillman Carbonates: Facile Synthesis of Isoxazoline N‐Oxides by Phosphorus Ylides

A phosphane‐catalyzed [4+1] annulation between nitroalkenes and Morita–Baylis–Hillman carbonates has been realized; this provides facile and diastereoselective access to polysubstituted isoxazoline N‐oxides in moderate to excellent yields. In the annulation, an in situ formed allylic phosphorus ylide presumably serves as a pivotal active intermediate. This reaction accordingly represents the first example of phosphorus ylide initiated [4+1] cyclization of nitroalkenes to give isoxazoline N‐oxides.     

Cascade reactions of nitrogen-and phosphorus-containing ylides with methyl diazoacetate and in situ generated diazocyclopropane

Reactions of pyridinium or phosphorus ylides with diazo esters are multistep processes. The first step is covalent bonding between the ylide C atom and the terminal N atom. This is followed by elimination of the ylide-forming molecule and successive addition of one or two ylide fragments. Depending on the nature of the starting reagents, this type of transformations leads to novel polyfunctional phosphorus ylides or, with pyridinium ylides, to polyalkyl 3,4(4,5)-diazaalkadienetri-or tetracarboxylates. A reaction of the in situ generated diazocyclopropane with methyl triphenylphosphoranylideneacetate stops at the first step, giving a cyclopropylazo-containing ylide. Reactions of the latter with acyl chlorides yield six-membered heterocyclic betaines with a triphenylphosphonium substituent. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 108–113, January, 2006.     

Polyhomologation: Synthesis of Novel Polymethylene Architectures by a Living Polymerization of Dimethylsulfoxonium Methylide

Not conventional polymerization of ethylene, but rather the title reaction has allowed access to the ω-functionalized tertiary polymethylene alcohols 1 . The ylide CH₂SOMe₂ is the methylene source in this living polymerization, and the chain length can be set by the initial ratio of ylide to organoborane.     

Synthesis of pyridinium ylide complexes of methylcobaloxime and crystal structure determination of [benzoyl(1-pyridinio)methanide]bis(dimethylglyoximato)methylcobalt benzene solvate

Summary Pyridinium ylide complexes of methylcobaloxime were synthesized by the treatment of an ylide with Co(Hdmg)₂ Me(SMe₂). The crystal structure of one of the complexes, [Co(Hdmg)₂Me C₅H₅NCHCOPh]C₆H₆ has been determined by x-ray diffraction techniques. The crystals are monoclinic, space group P2₁/c, witha = 10.456(5),b = 11.079(4),c = 24.58(1) Å, = 99.58(6), V = 2808 ų, Z = 4. The Co-C (ylide) bond distance is 2.18 Å and Co-C(methyl) 2.04 Å. C(ylide)-Co-C(methyl) bond angle is 174.9°. The crystal, i.r. and¹H n.m.r. data suggest that thetrans-influence of the ylide ligands is larger than that of py, Melm, OH₂ or PPh₃.     

Synthesis and Structure of Mixed Phosphonium-iodonium Ylide

A mixed phosphonium-iodonium ylide, phenyliodoniumethoxycarbonylmethylenetriphenylphosphorane borofluoride, was synthesized. Its structure was established by means of X-ray diffraction analysis. Temperature dependence of ¹H, ¹³C, and ³¹P spectra of the ylide synthesized was investigated. A dynamic equilibrium between Z and E-isomers was observed.     

Catalytic Wittig Reactions of Semi‐ and Nonstabilized Ylides Enabled by Ylide Tuning

The first examples of catalytic Wittig reactions with semistabilized and nonstabilized ylides are reported. These reactions were enabled by utilization of a masked base, sodium tert‐butyl carbonate, and/or ylide tuning. The acidity of the ylide‐forming proton was tuned by varying the electron density at the phosphorus center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity up to >95:5, E/Z.     

Reactions of 4,6-bis(acetyl)resorcinol with alkoxycarbonylalkylidene(triphenyl)phosphoranes. Preparation of coumarin derivatives

Reaction of compound 1 with ylide 2a affords compounds 3a, 3b and coumarins 4a, 5a, 5b, 6a in 77% total yield. Reaction of 1 with ylide 2b affords coumarin 4b . The acetylderivatives obtained, react further with ylides 2a-c to give pyrano[3,2-g]chromene-2,8-diones 6b-d .     

Photochemical reactions. 134th Communication. Photochemistry of 5,6-epoxy-5,6-dihydro-3,4-methano-β-ionone: Influence of a cyclopropane ring on the reactivity of an ylide intermediate

On ¹n,π*-excitation(λ > 347 nm), the diastereomeric methanoepoxyenones (E)- 6 undergo isomerization via C,O-cleavage of the oxirane leading to diastereomeric photoproducts ((E)- 5 →(E/Z)- 13 and 14 ; (E)- 6 →(E/Z)- 16 and 17 ). On ¹π,π*-excitation (λ = 254 nm) of either (E)- 5 ) or (E- 6 the photoproducts 9, 10 and 11 are formed. By laser flash photolysis (λ = 265 nm) the ylide intermediate 3 was detected, with a lifetime of 10 μs in MeCN at ambient temperature. Stern-Volmer analysis of the ylide quenching by MeOH disclosed that compounds 9 and 10 , but not 11 , arise from the ylide intermediate e .     

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.