Nickel-catalyzed reaction of butadiene with strained ring olefins: Formation of a four-membered cyclic compound

Reaction of butadiene with strained ring olefins such as norbornene, dicyclopentadiene etc. Gives an exo-methylene- and methyl-substituted four-membered cyclic compound (II). The effective catalysts are (n-Bu₃P)₂NiBr₂/NaBH₄ or /alkoxide $\text{1}\text{1}$ syn-π-crotylbis(triethyl phosphite)nickel hexafluorophosphate (IV), and tetrakis(triethyl phosphite)nickel/CF₃COOH $\text{1}\text{1}$. π-Crotyl complex IV reacts with the strained ring olefins to give the corresponding product similarly. It is concluded that the active species for this catalytic reaction is a nickel hydride and that this reaction proceeds through π-crotyl intermediate.     

An unexpected reaction between perfluoroisobutylene,caesium fluoride and haloforms

(CF₃)₂ CCF₂ reacts with CHCl, CHBr₃ and CHI₃ in the presence of CsF in diglyme, giving 3,3 - difluoro - 2 - halogeno - 4,4,5,5 - tetrakis(trifluoromethyl)cyclopent - 1 - enes. In the case of CHCl₃ the intermediate is shown to be 1,1 - dichloro - 3,3 - bis - (trifluoromethyl)allene (identified as an adduct with furan). 3,3 - Difluoro - 2 - chloro - 4,4,5,5 - tetrakis(trifluoromethyl)cyclopent - 1 - ene eliminates HCI under the action of CsF, giving a trimer of 3,3 - difluoro - 4,4,5,5 - tetrakis(trifluoromethyl)cyclopent - 1 - yne, namely, perfluorocarbon C₂₇F₄₂ (a Dewar benzene derivative).     

Reactions of 2,2,2-trifluorodiazoethane with carbon-nitrogen and carbon-oxygen multiple bonds

2,2,2-Trifluorodiazoethane reacts with trifluoroacetonitrile in the dark at room temperature to give a 2-(2,2,2-trifluoroethyl)-4, 5-bis(trifluoromethyl)triazole, the 1,2,3-triazole structure being preferred to the 1,2,4-isomer on the basis of the ¹⁹F n.m.r. spectrum. The diazoethane reacts more slowly with trichloroacetonitrile, again forming the N-alkylated triazole even in the presence of an excess of the nitrile. No identifiable adduct resulted with acetonitrile. Hexafluoroisopropyl-ideneimine is first N-alkylated and then undergoes addition to form 1-(2,2,2-trifluoro-1-trifluoromethyl)ethyl-4,5-bis(trifluoromethyl)-?-1,2,3-triazoline, but N-methylhexafluoroisopropylideneimine failed to react. Trifluoroacetaldehyde and trichloroacetaldehyde give mixtures of the ketone (formed by insertion of the CF₃CH group into the aldehyde CH bond) and the $\text{cis}$- and $\text{trans}$-oxirans, apparently $\text{via}$ a β-hydroxydiazoalkane.     

Preparation,stability, reactivity and synthetic utility of a cadmium stabilized complex of difluoromethylene phosphonic acid ester

Diethyl bromodifluoromethyl phosphonate reacts readily with cadmium metal to form a stable cadmium complex. Depending on solvent, this functionalized organocadmium reagent exhibits stability for days to months. It reacts with a variety of electrophiles and serves as a synthetically useful source for the introduction of the difluoromethylene phosphonate group into organic compounds.The synthetic utility of a wide variety of fluoromethylene phosphonium ylides has been a major effort in our laboratory over the past several years [1]. The generation and capture of difluoromethylene ylides ($\text{1}$) as a general route to difluoromethylene olefins has been of especial interest to us [2]. In an effort to increase the nucleophilicity of the ylide, we have attempted to prepare the analogous phosphonate ylide ($\text{2}$). Although we have achieved modest success [3] by $\text{insitu}$ capture of ($\text{2}$) in the reaction of

sodium dialkyl phosphites with diethyl bromodifluoromethylphosphonate ($\text{3}$), attempts to pregenerate ($\text{2}$), either from diethyl difluoromethylphosphonate ($\text{4}$) or ($\text{3}$), have met with little success. ($\text{2}$) appears to have minimal stability even at low temperatures, and scale up processes of synthetic value would seem to be difficult.     

Reactions of pyridinium t-butoxycarbonylmethylide with perfluoropropene and some fluoroaromatics

Perfluorotoluene, pentafluoropyridine, 3-chlorotetrafluoropyridine, and 3,5-dichlorotrifluoropyridine react with pyridinium t-butoxycarbonylmethylide (I) in acetonitrile at 0 – 20 °C to yield, $\text{via}$ nucleophilic displacement of a 4-F substituent in each case, the new pyridinium methylides (II)–(V), respectively. Treatment of perfluoropropene with (I) gives 1-(t-butoxycarbonyl)-2-fluoro-3-(trifluoromethyl)- pyrrolo[1,2-$\text{a}$]pyridine (VI) and 1,3-bis(t-butoxycarbonyl)-2- (1,2,2,2-tetrafluoroethyl)pyrrolo[1,2-$\text{a}$]pyridine (VII), formation of the latter (minor) product providing evidence that the former arises $\text{via}$ a stepwise dipolar cycloaddition.

     

Synthesis of fluoroamines,fluoroketones and difluoroamines

Aziridines $\text{1}$ and 2H-azirines $\text{2}$ are now very easy to prepare. These small rings are transformed in fluoroamine and fluoroketone by reaction with HF liquid or Olah reagent. Different compounds $\text{3}$, $\text{4}$ or $\text{5}$ are obtained. A lot of examples will be described.

a) Configuration of $\text{3}$ depends of the reagent (HF liquid or Olah reagent):

Mechanism of this reaction will be discuss.b) Some aziridines give a mixture of fluoroaminoisomers. Example:

With R = H, a mixture of $\text{6}$ (65 %) and $\text{7}$ (35 %) is obtained. It is possible to form quantitatively one regioisomer only, by using activating group on the nitrogen (R  CO₂tBu).c) From azirine $\text{2}$, formation of $\text{4}$ or $\text{5}$ dépends of the nature of substituents at carbon C-2. If a carbocation can be easily formed at C-2 carbon, only fluoroketone $\text{4}$ is isolated.Difluoroamine $\text{5}$ are obtained if carbon C-2 is a secondary or primary one. By using a modified Olah's reagent, we improve the yield.Application of this results on synthesis of fluorosteroïd compound will be presented:

     

Perhalogenmethylmercapto-heterocyclen,IX (perchlormethylmercapto)- und (perfluormethylmercapto)pyridine

Methods of substituting pyridine by perhalogenomethylmercapto groups are discussed. The side chain chlorination of 2-(methylmercapto)pyridine leads gradually to 2-(trichloromethylmercapto)pyridine hydrochloride ($\text{1a}$) and 2-(trichloromethylmercapto)pyridine ($\text{1b}$). Neither a direct reaction of pyridine with CF₃SCl nor the way over a Grignard reaction or a sulfenylcarboxylate lead to CF₃S-substituted products. Reactions of pyridine and bromopyridines with Hg(SCF₃)₂ yield 1:1-adducts ($\text{2a-d}$) only. Lithium tetrakis(1,2-dihydro-1-pyridyl)aluminate (LDPA) reacts with CF₃SCl to give 3-(trifluoromethylmercapto)pyridine ($\text{3}$); in addition a disubstituted product can be identified massspectroscopically. ¹H- and ¹⁹F-NMR-spectra are reported.     

The decarboxyla tive dehydration of 3-hydroxycarboxylic acids with dimethyl-formamide-dimethylacetal - evidence for a zwitterionic intermediate

Dimethylformamide dimethylacetal ($\text{1}$) and 3-hydroxycarboxylic acids ($\text{2}$) react with formation of esters ($\text{4}$) and olefins ($\text{5}$). Evidence is provided that $\text{5}$ is generated via an E1/E2-type fragmentation of a zwitterionic intermediate

. (Scheme 1).     

Silicon in synthesis: 1-trimethylsilyl-1-methoxy allene; a reagent for the direct conversion of aliphatic aldehydes into 2-trimethylsilyl furans

3-Lithio 1-trimethylsilyl-1-methoxy allene $\text{4}$ reacts with aldehydes to give adducts that are readily transformed into 2-trimethylsilyl furans.     

Synthesis of a flav-3-en-3-ol via cinnamylphenol

Vinyl quinone methide ($\text{1}$) reacts with polyphenols to give cinnamylphenols ($\text{4}$) and neo-flavanoids ($\text{5}$). Oxidation of cinnamylphenol ($\text{4}$b) leads to malvidin ($\text{10}$) via the isolated intermediate flav-3-en-3o1 ($\text{8}$b).     

Fluorocarbon derivatives of nitrogen. Part 11. Synthesis of some 2-(trifluoromethyl)imidazo[1,2-a]pyridines from trifluoroacetonitrile

3-(t-Butoxycarbonyl)-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine, prepared from trifluoroacetonitrile and pyridinium t-butoxycarbonylmethylide, reacts smoothly with trifluoroacetic acid to provide 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine-3-carboxylic acid, which gives 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine when heated. 3-Cyano-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine can be obtained $\text{via}$ treatment of trifluoroacetonitrile with pyridinium cyanomethylide, which is sufficiently reactive to effect nucleophilic displacement of fluorine from pentafluoropyridine under mild conditions [→pyridinium cyano(tetrafluoro-4-pyridyl)methylide].     

Free-radical additions of ethers to fluorinated olefins

γ-Ray and peroxide-initiated additions of dimethylether to F-cyclobutene, F-cyclopentene, and F-cyclohexene give mixtures of $\text{cis}$- and $\text{trans}$-adducts and the stereochemistry of these processes will be discussed. A comparison of the reactivity of hexafluoropropene

towards radical additions of various cyclic ethers will be made which supports a rationale of the stabilising effect of oxygen on an adjacent radical centre.Bromination and chlorination of the adducts provides, at first sight, surprising variations in selectivity.