Vinyliodonium salts : their stereospecific synthesis and reactions as the activated vinyl halides

Vinyliodonium salts $\text{2}$ were synthesized from vinylsilanes $\text{1}$ by the reaction with iodosylbenzene and triethyloxonium tetrafluoroborate. The reaction occurs stereospecifically with retention of configuration. Vinyliodonium salts $\text{2}$ are highly effective as the activated species of vinyl iodides. Thus, a variety of substituted olefins including α-cyano and α-nitro olefins, vinyl sulfides, vinyl halides, and α,β-unsaturated esters, were prepared from $\text{2}$ under mild reaction conditions.     

Bridged and unbridged norbornyl cations

The solvolysis rates and products of 6-substituted 2-norbornyl-p-toluene-sulfonates $\text{1}$ and $\text{5}$ are controlled by 1,3-bridging, i.e. by the degree of bonding between C(6) and C(2) in the intermediate norbornyl cations.     

Dependence of transmission of conjugation through cyclopropane ring into vinyl group on electron demand of substituent

The placement of a methoxycarbonyl or a cyano group on the cyclopropane ring in spiro-vinylcyclopropanes ($\text{7a}$, $\text{7b}$) causes a drain of electrons from the vinyl group through the ring into the electron demanding substituent, precluding their [2+2]cycloaddition with TCNE but not with the stronger electrophilic olefin CSI ($\text{7}$ → $\text{8}$), whereas the placement of a hydroxymethyl group renders the vinyl group reactive toward TCNE ($\text{9}$ → $\text{13}$).     

Photochemistry of organic halides: Some interesting features of the photobehaviour of vinyl halides and vinylidine dihalides derived from camphene

A study of the photochemistry of vinylidine dihalides $\text{1}$ and $\text{2}$ and vinylhalides $\text{4}$ and $\text{5}$ revealed some interesting differences in their photobehaviour. This study led to uncover an important constraint in the generation of vinyl cations from certain α-unsubstituted vinyl halides such as $\text{4}$.     

Emission spectra of supersonically cooled chloroacetylene cations

The ā²Π_Ω → X?²Π_Ω, Ω = $\text{3}\text{2}$, $\text{1}\text{2}$ emission spectra of rotationally cooled chloro- and deuterochloro-acetylene cations have been obtained by electron-impact ionisation of a seeded helium supersonic free jet. The resultant spectral improvements lead to the identification of the spin-orbit components and isotope splittings and to a vibrational assignment of the prominent bands. The vibrational frequencies could be determined to within ±1 cm^?1 for many of the fundamentals for the cations in the X?²Π_Ω and ā²Π_Ω electronic states.     

o-quinone methides 2. Stereoselectivity in cycloaddition reactions of o-quinone methides with vinyl ethers

Cycloaddition reactions between vinyl ethers 3 and $\text{o}$-quinone methides 2, thermally generated from 2-hydroxybenzyl alcohols 1, have been studied. The structure and conformational preferences of the 4-substituted 2-ethoxy-(2,3)-dihydro-2$\text{H}$-benzopyrans 4–9 obtained, which show new interesting features, are discussed together with competitive kinetic data. The cycloaddition process is concerted and involves $\text{o}$-quinone methides in the $\text{E}$-configuration. The OEt-$\text{endo}$ transition state seems to be preferred with ethyl vinyl ether and $\text{Z}$-1-propenyl ethyl ether, whereas with $\text{E}$-1-propenyl ethyl ether the stereoselectivity of the cycloaddition process depends on substituents on the methylene group of the starting alcohol 1. These results are discussed in terms of $\text{endo}$ and $\text{exo}$ preference of the propenyl ether methyl group.     

Carbopalladation of β-allenylmalonates : a way to cyclopentenyl or vinylcyclopropyl derivatives.

The palladium-catalyzed addition of a vinyl or aryl halide to the enolate of β-allenyl malonate $\text{2}$ leads to the formation of either of the two cyclized products $\text{3}$ and $\text{4}$ depending mainly on the bulk of the starting unsaturated halide.     

Radical-initiated polyolefinic cyclizations in linear triquinane synthesis. model studies and total synthesis of (±)-hirsutene

Details of a novel radical-initiated polyolefinic cyclization approach to linear condensed cyclopentanoids are reported. The strategy is executed in three stages: (1) Sn2′-anti opening of a vinyl lactone to produce a trans-3,5-disubstituted cyclopentene, (2) rapid elaboration to a cyclization precursor, and (3) single step tandem radical cyclization to produce a cis-anticis tricyclo[3.3.0]undecane. Model substrates $\text{16a}$ and $\text{16b}$ give high yields of tricyclic products $\text{17}$ and $\text{18}$, respectively. An effort to rationalize the interesting endo selectivity via the Beckwith transition state model is proposed. Cyclizations of $\text{28}$ and $\text{29}$ to $\text{30}$ and $\text{31}$ demonstrate the viability of a tandem hexenyl-hexynyl cyclization. The work culminates with a total synthesis of (±)hirsutene. A selective approach to methyl substituted vinyl lactones by Claisen rearrangement-phenylselenolactonization-elimination of acetoxy cyclopentenols is exemplified by the synthesis of $\text{12}$. Tandem cyclization of $\text{38}$ produces hirsutene ($\text{1}$) in a single step. Alternatively, cyclization of $\text{37}$ yields trimethylsilyl hirsutene.     

Selenosulfonation of acetylenes. Preparation of novel β-(phenylseleno)vinyl sulfones

Se-Phenyl p-tolueneselenosulfonate ($\text{1}$) undergoes thermal addition to acetylenes to afford β-(phenylseleno)vinyl sulfone adducts $\text{2}$ in a stereo- and regioselective fashion.     

A novel synthesis of allyl vinyl ethers

Base-promoted reaction of dimethyl diazomethylphosphonate ($\text{2}$) with aliphatic ketones in the presence of allylic alcohols affords aldehydic allyl vinyl ethers ($\text{3}$).     

Epimerization of bicyclic vinyl tertiary-alcohols via [2,3] sigmatropic rearrangement

General methods for inverting the stereochemisty of vinyl $\text{tertiary}$-alcohols such as $\text{2}$ and $\text{5}$ into $\text{3}$ and $\text{8}$ respectively are described. The procedures employ a [2,3] sulfoxide rearrangement and will facilitate the extended use of the oxy-Cope rearrangement to a variety of related ring systems.     

Emission spectra of supersonically cooled methyldiacetylene cations

The ā²E → X?²E (Σ= + $\text{1}\text{2}$, - $\text{1}\text{2}$) electronic transitions of rotationally/vibrationally cooled CH₃CCCCH^- cation, as well as the d₁-/d₃-/d₄-substituted species, were studied by emission spectroscopy. Ion emission was obtained by electron impact on the neutral species seeded in a helium supersonic free jet. Vibrational frequencies in both electronic states are inferred to within ±1 cm^-1. Spin-orbit splittings are observed and interpreted on the basis of non-linear vibronic couplings. Rotational subbands are observed, yielding rotational and Coriolis parameters as well as rotational temperatures.     

The Stereochemistry of simple enols in solution

On the basis of their ¹H n.m.r. spectra it is concluded that vinyl alcohol and $\text{trans}$-1-propenol exist mainly in the $\text{syn}$-conformation and that $\text{cis}$-1-propenol and 2-methyl-1-propenyl exist mainly in the $\text{anti}$ conformation.     

[2+2]-Cycloadditionen von vinylkationen

The vinylbromides $\text{1a}$ and $\text{1b}$ are allowed to react ith AgBF₄ and AgPF₆ in the presence of various olefins in CH₂Cl₂ as the solvent. Except for the reaction of cyclopentene with $\text{1a}$ all other olefins used, react with vinyl cation $\text{2}$ to form the cycloaddition products $\text{7}$, $\text{8a}$ and $\text{8b}$ in high yields.     

Synthesis applications of aza-cope rearrangements.: Stereocontrolled synthesis of cyclohepta [b]pyroolidines1

Both $\text{cis}$- and $\text{trans}$-3a-aryl-4-oxo-decahydrocyclohepta[b]pyrroles can be prepared in stereocontrolled fashions by the reaction of 2-amino-1-(1-phenyl- vinyl)cyclohexanols with formaldehyde and acid.     

Formation of a dinaphthanthracene by a stilbene-like photocyclization

Photocyclization of 1,3-bis[2-(2-naphthyl)vinyl]benzene leads regioselectively to dinaphth[1,2-$\text{a}$:2′,1′-$\text{j}$]anthracene without the need for a blocking bromine substituent at C-2 in the starting material as assumed previously by other workers.     

Novel oxidative rearrangement of β,γ-unsaturated ketone hydrazones on iodination in base

Iodination of the bicyclic enone hydrazone $\text{3}$ in excess triethylamine gave, in addition to the expected vinyl iodide $\text{4}$, the rearranged aromatic product $\text{5}$.     

Heteroatom directed β-lithiation of a vinyl ether

Oxygen directed β-deprotonation of a vinyl ether leads to $\text{Z}$ substituted enol ethers. The stereoselective elaboration to a naturally occuring $\text{threo}$ 1,3-diol is described.     

Epimeric 2-norbornyl cations in the solvolysis of 6-exo- and 6-endo-substituted 2-exo-norbornyl p-toluenesulfonates

Solvolysis of 6-exo- and 6-endo-substituted 2-exo-norbornyl tosylates $\text{1}$ and $\text{3}$, respectively, yields identical or different product mixtures depending on the inductive effect of the substituent, indicating that induction involves graded σ-participation.     

Orientation effects in reactions of allenyl cations with styrene

Allenyl cations, generated $\text{in}$$\text{situ}$ from allenyl or alkynyl halides and Ag⁺, attack styrene at the side chain or at the aromatic nucleus. The allenyl/alkynyl product ratio is dependent on the structure of the precursor halide except for highly substituted systems.