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A highly efficient method has been developed for the synthesis of 1-vinylindole based on the vinylation of indole by acetylene at atmospheric pressure using the superbase KOH–DMSO catalytic system. The method allows the preparation of the 1-vinylindole in 94% yield with a purity of 99% (after a single distillation of the crude product).

Tertiary propargyl alcohols bearing aryl or heteroaryl substituents are readily accessible from the corresponding ketones and acetylene under atmospheric pressure using a superbasic system.

Vinyl ether derived from tertiary acetylenic alcohols have not been reported so far. The reason is that such alcohols are unstable on heating in the presence of bases (classical retro-Favorskii reaction) [1–3]. Nevertheless, insofar as the Favorskii reaction is reversible, we can presume that O-vinylation of a tertiary acetylenic alcohol present in the reaction mixture even at a small concentration should eventually lead to expected vinyl ether due to continuous displacement of the equilibrium (Scheme 1). Therefore, vinyl ethers of tertiary acetylenic alcohols could be obtained in one step by heating ketones with acetylene in the presence of a base. Screening of the reaction conditions and superbasic catalytic systems, as well as of ketones and acetylenic compounds used as reactants, has shown that 1-ethynylcyclohexyl vinyl ether (III) is indeed formed upon treatment of cyclohexanone (I) with acetylene in the presence of a base. In the reaction performed in a suspension of KOH in DMSO (molar ratio I–KOH 1 : 1) at 90°C under acetylene pressure the yield of vinyl ether III reached 40% (Scheme 2). An important condition is acetylene pressure which ensures its high concentration in the liquid phase and favors displacement of equilibrium toward formation of 1-ethynylcyclohexan-1-ol (II) which then undergoes vinylation (Scheme 2). ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 6, pp. 858–859. © Pleiades Publishing, Ltd., 2012. Original Russian Text © B.A. Trofimov, E.Yu. Shmidt, I.A. Bidusenko, E.V. Ivanova, N.V. Zorina, A.I. Mikhaleva, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48, No. 6, pp. 860–861.

Despite poor yield of the target product (25%), the reaction of acetophenone oxime (I) with phenylacetylene (II) in superbasic medium (Trofimov reaction) [1–4], leading to 2,5-diphenyl-1H-pyrrole (III), attracts interest from the preparative viewpoint, for alternative methods include a number of steps [5], and the overall yield (calculated with account taken of all steps) is comparable to that in the Trofimov synthesis. Determination of structure of by-products in the reaction of oxime I with acetylene II may be useful for understanding its mechanism and further optimization to enhance its preparative efficiency. We were the first to isolate from the product mixture (LiOH–DMSO, 130°C, 5 h) 6% of 1,3,5-triphenylbenzene (V) together with pyrrole III and acetophenone IV (deoximation product of initial oxime I) (Scheme 1). However, this assumption was not confirmed experimentally. We also found that under the given conditions compound V cannot be formed as a result of autocondensation of oxime I or ketone IV. Presumably, O-vinyl oxime VI which is the primary intermediate in the synthesis of pyrroles from ketone oximes and acetylene [6] (Scheme 2) undergoes rearrangement into nitrone VII (as reported in [7] for cyclohexanone oxime O-allyl ether). Enhanced CH acidity of the CH3 group in VII due to strong electron-withdrawing effect of the N-oxide fragment favors aldolization (crotonization) of VII with acetophenone IV. The condensation of azatriene VIII thus formed with the second acetophenone molecule gives azatetraene IX, and cyclization of the latter, followed by aromatization of dihydrobenzene X via elimination of vinylnitrone XI, yields triphenylbenzene V. Compound XI can be converted into acetophenone oxime (I).

Ketone oxime O-vinyl ethers having alkyl or phenyl radicals react with trifluoroacetic anhydride in ether in the presence of pyridine, yielding 43-54% of the corresponding ketone oxime O-(trans-4,4,4-trifluoro-3-oxo-1-butenyl) ethers with high stereoselectivity.

The oxime of Δ5-pregnen-3β-ol-20-one reacts with acetylene in the KOH-DMSO system to form a mixture of products containing 3β-vinyloxy-17β-(1-vinyl-2-pyrrolyl)-Δ5-androstene as the major product (63% yield) and also the O-vinyloxime of 3β-vinyloxy-Δ5-pregnen-20-one (10%), 3β-vinyloxy-17α- and 3β-vinyloxy-17β-Δ5-pregnen-20-one (25%, 1:4 ratio).

It is known that ketone oximes react with acetylene in the superbasic system KOH–DMSO to give O-vinyloximes which readily undergo rearrangement into pyrroles (Trofimov reaction [1–3]). However, vinylation of 5-phenyl-1-vinyl-1H-pyrrole-2-carbaldehyde oxime (I) under analogous conditions gave exclusively 5-phenyl-1-vinyl-1H-pyrrole-2-carbonitrile (III, yield 67%) instead of expected O-vinyloxime II. It could be presumed that compound III was formed via dehydration of initial oxime I. Dehydration of aldehyde oximes to the corresponding nitriles in the system KOH–DMSO was described in [4]. However, oxime I almost did not undergo dehydration in the absence of acetylene (the yield of nitrile III did not exceed 4%). Therefore, we concluded that 5-phenyl-1vinyl-1H-pyrrol-2-carbonitrile (III) is formed as a result of elimination of vinyl alcohol (acetaldehyde) from O-vinyloxime II.

1-Vinyl-2-phenylazopyrroles react with alcohols in the presence of acids or PdCl2 to give 1-(1-alkoxyethyl)-2-phenylazopyrroles in up to 49% yield. In the presence of trifluoroacetic acid 2-methylquinoline unexpectedly formed (yield up to 26%) involving into the reaction the phenylazo and 1-vinyl groups.

The oxime of 2-acetylcoumarone reacts with acetylene under pressure in the system KOH-DMSO unusually readily forming 2-(2-pyrrolyl)coumarone and the corresponding O-vinyl oxime. Under more rigid conditions 2-(1-vinyl-2-pyrrolyl)coumarone is formed. The possibility of a two-stage transformation of 2-acylcoumarones into 2-pyrrolylcoumarones has therefore been demonstrated for the first time.

Steroidal ketone oximes, namely pregnenolone oxime, Δ5-cholesten-3-one oxime, and progesterone dioxime react with acetylene in superbasic systems (Trofimov reaction) to afford steroid-pyrrole assemblies. The process is accompanied by prototropic migration of double bonds in the steroid fragment and vinylation of hydroxy groups in sterols with acetylene. The O-vinyl group can readily be removed by methanolysis.

Literature data on the alkylation of phenolic compounds by mono-, sesqui-, and diterpenes in the presence of various catalysts are reviewed.

The reaction of N-vinylpyrroles with hydrogen chloride at low temperatures has been studied. At −80‡C the α-position of the heterocycle is protonated while at higher temperatures products of HCl addition to the double bond and protonation of the ring are formed. The C-Cl bond of the chloroethyl radical of the product of HCl addition to the vinyl group is readily dissociated resulting in reversible interconversion of the enantiomers of the racemic mixture which is formed. By introducing a diastereotopic marker (i-Pr) this interconversion can be monitored by dynamic NMR. It has been found that the energy of this process varies with HCl concentration and with the substituents on the ring.

Die bei der Luftoxidation von Isopimarsaure (I) in Gegenwart katalytischer Mengen von Co-stearat bei 75°C entstehenden Produkte enthalten als neutralen Anteil (10-15%) die Hydroxylverbindung (II) neben den oxidierten Sauren (III) und (IV).