Arenes acetylene derivative

Addition reactions of sulphenyl halides (in particular chlorides) to acetylene derivatives have been extensively explored and recently reviewed (Modena and Scorrano, 1968). Although free radical processes may be involved under specific conditions, the addition of both arene-and alkanesulphenyl halides normally occurs by an ionic mechanism, the sulphenyl halide sulphur being the electrophilic centre. 

Chromium trichloride ethylmagnesium bromide Arenes from acetylene derivatives O... 

Ca. 5% excess dry paraformaldehyde added in small portions with occasional cooling to gently refluxing ethereal p-tolyllithium prepared from p-iodotoluene and lithium, stirring continued 10-15 min. p-methylbenzyl alcohol. Y 95%. — It is not necessary to prepare monomeric formaldehyde from the paraformaldehyde. F. e., also C-hydroxymethylation of acetylene derivatives, s. A. Schaap, L. Brandsma, and J. F. Arens, R. 8A, 1200 (1965). 

Di(cobalt tetracarbonyl)mercury Arenes from acetylene derivatives s. 16, 751... 

Across carbon multiple bonds Ketenes are very reactive in [2+2] cycloaddition reactions to numerous double-bonded substrates. They form four-membered ring cycloadducts, even with regular olefins. In the reaction of ketenes with acetylene derivatives sometimes also four-membered ring [2+2] cycloadducts are obtained. The isolation of ethoxycy-clobutenones in the thermolysis of ethoxyacetylenes was interpreted by Nieuwenhuis and Arens to occur via a [2+2] cycloaddition reaction of the generated ketene with the starting material. This type of reaction is also observed when dimethylketene is reacted with ethoxyacetylene to give a 83 % yield of the cyclobutenone . The ketene also reacts with ethoxyacetylene to give the cyclobutenone derivative 95. ... 

Figure 50. Proposed mechanism of formation of arene-chromium derivatives from acetylenes and chromium-aryl complexes.

In a related reaction, heating ketones in the presence of TlClsOTf leads to 1,3,5-trisubstituted arenes. " Nitriles react with 2 mol of acetylene, in the presence of a cobalt catalyst, to give 2-substituted pyridines. " Triketones fix nitrogen gas in the presence of TiCU and lithium metal to form bicyclic pyrrole derivatives. " ... 

A different synthetic access to a 1 -metallacyclopropene, which can be a versatile organometallic synthon, is displayed in Scheme 33. The mono-alkyne derivatives of W(IV)-calix[4]arene are easily accessible through the thermal displacement of cyclohexene from 32 using the appropriate acetylenes. The reaction led to complexes 34 and 172-174. The proposed 3-metallacyclopropene has been confirmed from the spectroscopic and the X-ray data. The H NMR data reveal a cone conformation of the calixarene with a four-fold symmetry, for which the... 

Abbreviations arene, i/6-benzene or substituted benzene derivative bipy, 2,2 -bipyridyl Bu, Bu", Bu, iso-, n-, or rerf-butyl COD, 1,5-cyclo-octadiene Cp, /5-C5H5 DAD, dimethyl-acetylene dicarboxylate dam, 1,2-bis(diphenylarsino)methane DBA, dibenzylideneacetone DMF, A. A -dimethylformamide dpe, l,2-bis(diphenylphosphino)ethane dpen, os-l,2-bis(di-phenylphosphino)ethylene dpm, 1,2-bis(diphenylphosphino)methane ESR, electron spin resonance F6-acac, hexafluoroacetylacetone FN, fumaronitrile MA, maleic anhydride Me, methyl MLCT, metal ligand charge transfer phen, 1,10-phenanthroline Pr , Pr", iso- or n-propyl py, pyridine RT, room temperature TCNE, tetracyanoethylene tetraphos, (Ph2PCH2CH2)jP THF, tctrahydrofuran Xylyl, 2,6-Me2C6H3. 

Ortho photocycloaddition to benzene of derivatives of acetylene and maleimide proceeds via excitation of the alkyne or the maleimide. A few other alkenes follow the same route to ortho photocycloadducts among those are dichlorovinylene carbonate and some alkenes in which the double bond is conjugated with a cyano, carbonyl, or phenyl group, which makes it possible to excite them in the presence of the arene. 

A remarkable cobalt-arene complex was also isolated from the metal vapor reaction of cobalt atoms with toluene (Scheme 13) and subsequent addition of an aUcyne (acetylene, butyne, or BTSA). According to EPR spectra, compounds of the type (toluene)Co(alkyne) are 19-electron complexes of near-axial symmetry where the aUcyne acts as a four-electron ligand on the cobalt atom. The methyl derivative has been structurally characterized with Co-Caikyne distances of 1.88 and 1.90 A, and a C C distance of 1.254 A (Figure 11). 

A major initial limitation of the benzocyclobutene approach to o-quinodimethanes was the lack of efficient, large-scale syntheses for many specifically substituted derivatives. Fortunately, recent developments have lemov much of this impediment. Q>nceptually, the synthesis of benzocyclobutenes from aromatic precursors can be envisaged in only a limited number of ways. These include [2 -i- 2] cycloadditions involving benzynes and alkenes, intramolecular cyclization on to a benzyne, cyclizations involving arene anions, and electrocyclic closure of o-quinodimethanes. Benzocyclobutene derivatives can also be prepared by aromatization of bicyclo[4.2.0]octanes. Detailed discussion of variations to these approaches can be found in the cited reviews. The cobalt catalyzed co-oligomerization of 1,5-hexadiynes with al-kynes, especially bis(trimethylsilyl)acetylene, has also been employed for the preparation of specifically substituted benzocyclobutenes. In the latter case the cyclobutenes are often not isolated but converted directly to o-quinodimethanes and subsequent products. ... 

Yamazaki s complex (Structure 5) contains two alkyne molecules linked together to form a five-membered metallacycle. Arene-solvated cobalt atoms, obtained by reacting cobalt vapor and arenes, have been used by Italian workers to promote the conversion of a,w-dialkynes and nitriles giving alkynyl-substituted pyridines [20]. -Tolueneiron(0) complexes have also been utilized for the co-cyclotrimerization of acetylene and alkyl cyanides or benzonitrile giving a-substituted pyridine derivatives. However, the catalytic transformation to the industrially important 2-vinylpyridine fails in this case acrylonitrile cannot be co-cyclotrimerized with acetylene at the iron catalyst [17]. 

The more complex [2 -f 2 + 2] cycloisomerization reaction of acetylene units is also catalyzed by transition metal-alkyne n complexation and can be readily utilized for the synthesis of a variety of polysubstimted benzene derivatives in a straightforward manner (10, 352, 353). Recently, this methodology has been applied to the cyclization of 15-membered, nitrogen-containing di- and triacetylenic macrocycles. Upon coordination with Pd(0) to the triacetylenic macrocycle at ambient temperature, the ti-coordinated Pd(0) complex results. Subsequent refluxing of this species in toluene promotes cycloisomerization to the hexasubstituted arene (354) (Scheme 28). The Rh(I) [e.g., RhCl(CO)(PPh3)2] complex also catalyzes these same transformations in high (>80%) yields. 

---