Acid-Catalyzed Isomerization of 1-Halo-2-Arylthioalk-1-Enes

1-Halo-2-arylthioalk-1-enes, the anti-Markovnikov adducts of 1,2-halosulfenylation of terminal alkynes containing propargyl hydrogen atoms, were found to transform into a mixture of E - and Z -isomers of 1-halo-2-arylthioalk-2-enes under acid catalysis conditions. A plausible mechanism of rearrangement is proposed. The Markovnikov adducts 2-halo-1-arylthioalk-1-enes were partially converted into their cis -form under similar conditions. The halosulfenylation products of 1-phenylpent-1-yne did not show the signs of double-bond migration in the presence of an acid; only partial isomerization of the E - to the Z -isomers took place.     

[4+2]-Cyclodimer of sabinone: formation,crystal structure,and NMR spectra

Oxidation of (+)-sabinol, (1S,3R,5S)-1-isopropyl-4-methylidenebicyclo[3.1.0]hexan-3-ol, by active MnO₂ afforded not the expected sabinone but only its [4+2]-cyclodimer. The molecular structure of the latter was established by X-ray diffraction analysis. The ¹H and ¹³C NMR spectra of this cyclodimer were interpreted using 2D NMR spectroscopy.     

[1+2]-cycloadditionen von isocyaniden an indiamine

Arylisocyanides and aroylisocyanides add to ynediamines in [1+2]- cycloaddition reactions to yield the corresponding cyclopropenonimines; electron withdrawing substituents in the arylisocyanides accelerate the rate of addition.     

[1+2] Addition of disulfides to phosphaalkenes

We are the first to report the [1+2] addition of disulfides to phosphaalkenes in the case of C-(N,N-dimethylaminomethylene)-P-phenylphosphine (I) and dimethyl disulfide (II). This reaction proceeds with the complete cleavage of the P-C double bond and the addition of two equivalents of the disulfide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 186–187, January, 1991.     

Catalytic [2+1]-cycloaddition of ethyl diazoacetate to fullerene [60]

Cyclopropanation of C₆₀-fullerene was performed with ethyl diazoacetate in the presence of Pd(PPh₃)₄ catalyst. A probable reaction mechanism is suggested.     

A Novel Acid-Catalyzed Isomerization of Aib-Containing Thiodipeptides

The use of amino thioacids in the `azirine/oxazolone method' led to completely epimerized Aib-containing endothiodipeptides (Aib=2-aminoisobutyric acid). It could be established that the epimerization occurred during the acidic hydrolysis of the primarily formed dipeptide thioanilides in which the thiocarbonyl group was shifted from the last to the penultimate amino-acid residue. Several conditions for the hydrolysis were tested, and, in some of them, the degree of epimerization could be reduced. By treatment of the Aib-containing dipeptide thioanilides 21 with ZnCl₂ in AcOH followed by HCl in AcOH, the isomeric endothiodipeptide anilides 25 were formed, i.e., the thiocarbonyl group was again shifted from the last to the penultimate amino acid residue. Under optimized reaction conditions, this novel isomerization proceeded in high yields and without any epimerization. Two conceivable mechanisms are proposed in Scheme 12. X-Ray diffraction analyses were performed for Z−Gly−Aib-Ψ(CS)−N(Me)Ph ( 21f ) and the isomeric Z−Gly-Ψ(CS)−Aib−N(Me)Ph ( 25f ).     

Catalytic [2+1] cycloaddition of diazo compounds to [60]fullerene

A catalytic method for the efficient synthesis of 5,6-open and 6,6-closed (2π+1π) fullerene adducts by [2+1] cycloaddition of ethyl 2-alkyl(hetaryl)-2-diazoacetates to [60]fullerene in the presence of a three-component catalyst Pd(acac)₂—PPh₃—Et₃Al have been developed.     

One-pot synthesis of [1+1] and 62-membered [2+2] Schiff base macrocycles

New [1+1] and 62-membered [2+2] Schiff base macrocycles containing a 2,6-diamidopyridine subunit have been synthesized by condensation reaction of the precursors pyridine-2,6-dicarboxamide and 1,10-bis(20-formylphenyloxy)decane in the presence of phosphoric acid via a one-pot process. The cyclocondensed products were effectively isolated by gel column chromatography and characterized by ~1H NMR, FTIR, mass spectrometry and X-ray analysis. The two macrocycles have a twisted structure, and not an open ‘circular' conformation in the solid state.     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Enantioselective sensing of amines based on [1 + 1]-, [2 + 2]-, and [1 + 2]-condensation with fluxional arylacetylene-derived dialdehydes

Four induced circular dichroism (ICD) probes exhibiting a stereodynamic arylacetylene framework and terminal aldehyde units have been prepared. The CD silent sensors generate a strong chiroptical response to substrate-controlled induction of axial chirality upon selective [1 + 1]-, [2 + 2]-, and [1 + 2]-condensation. The intense Cotton effects can be exploited for in situ ICD analysis of the absolute configuration and ee of a wide range of amines.     

Acid-Catalyzed [3,3]-Sigmatropic Rearrangements of N-Propargylanilines

The acid-catalyzed rearrangement of N-(1′,1′-dimethylprop-2′-ynyl)-, N-(1′-methylprop-2′-ynyl)-, and N-(1′-arylprop-2′-ynyl)-2,6-, 2,4,6-, 2,3,5,6-, and 2,3,4,5,6-substituted anilines in mixtures of 1N aqueous H₂SO₄ and ROH such as EtOH, PrOH, BuOH etc., or in CDCl₃ or CCl₄ in the presence of 4 to 9 mol-equiv. trifluoroacetic acid (TFA)has been investigated (cf. Scheme 12-25 and Tables 6 and 7). The rearrangement of N-(3′-X-1′,1′-dimethyl-prop-2′-ynyl)-2,6- and 2,4,6-trimethylanilines (X = Cl, Br, I) in CDCl₃/TFA occurs already at 20° with τ_1/2 of ca. 1 to 5 h to yield the corresponding 6-(1-X-3′-methylbuta-1,2′-dienyl)-2,6-dimethyl- or 2,4,6-trimethylcyclohexa-2,4-dien-1-iminium ions (cf. Scheme 13 and Footnotes 26 and 34) When the 4 position is not substituted, a consecutive [3,3]-sigmatropic rearrangement takes place to yield 2,6-dimethyl-4-(3′-X-1′,1′-dimethylprop-2′-ynyl)anilines (cf. Footnotes 26 and 34). A comparable behavior is exhibited by N-(3′-chloro-1′-phenylprop-2′-ynyl)-2,6-dimethylaniline ( 45 ., cf. Table 7). The acid-catalyzed rearrangement of the anilines with a Cl substituent at C(3′) in 1N aqueous H₂SO₄/ROH at 85-95°, in addition, leads to the formation of 7-chlorotricyclo[3.2.1.0^2,7]oct-3-en-8-ones as the result of an intramolecular Diels-Alder reaction of the primarily formed iminium ions followed by hydrolysis of the iminium function (or vice versa; cf. Schemes 13,23, and 25 as well as Table 7). When there is no X substituent at C(1′) of the iminium-ion intermediate, a [1,2]-sigmatropic shift of the allenyl moiety at C(6) occurs in competition to the [3,3]-sigmatropic rearrangement to yield the corresponding 3-allenyl-substituted anilines (cf. Schemes 12,14–18, and 20 as well as Tables 6 and 7). The rearrangement of (?)?(S)-N-(1′-phenylprop-2′-ynyl)-2,6-dimethylaniline ((?)- 38 ; cf. Table 7) in a mixture of 1N H₂SO₄/PrOH at 86° leads to the formation of (?)-(R)-3-(3′-phenylpropa-1′,2′-dienyl)-2,6-dimethylaniline ((?)- 91 ), (+)-(E)- and (?)-(Z)-6-benzylidene-1,5-dimethyltricyclo[3.2.1.0^2′7]oct-3-en-8-one ((+)-(E)- and (?)-(Z)- 92 , respectively), and (?)-(S)-2,6-dimethyl-4-( 1′-phenylprop-2′-ynyl)aniline((?)- 93 ). Recovered starting material (10%) showed a loss of 18% of its original optical purity. On the other hand, (+)-(E)- and (?)-(Z)- 92 showed the same optical purity as (minus;)- 38 , as expected for intramolecular concerted processes. The CD of (+)-(E)- and (?)-(Z)- 92 clearly showed that their tricyclic skeletons possess enantiomorphic structures (cf. Fig. 1). Similar results were obtained from the acid-catalyzed rearrangement of (?)-(S)-N-(3′-chloro-1′phenylprop-2′-ynyl)-2,6-dimethylaniline ((?)- 45 ; cf. Table 7). The recovered starting material exhibited in this case a loss of 48% of its original optical purity, showing that the Cl substituent favors the heterolytic cleavage of the N–C(1′) bond in (?)- 45. A still higher degree (78%) of loss of optical activity of the starting aniline was observed in the acid-catalyzed rearrangement of (?)-(S)-2,6-dimethyl-N-[1′-(p-tolyl)prop-2′-ynyl]aniline ((?)- 42 ; cf. Scheme 25). N-[1′-(p-anisyl)prop-2-ynyl]-2,4,6-trimethylaniline( 43 ; cf. Scheme 25) underwent no acid-catalyzed [3,3]-sigmatropic rearrangement at all. The acid-catalyzed rearrangement of N-(1′,1′-dimethylprop-2′-ynyl)aniline ( 25 ; cf. Scheme 10) in 1N H₂SO₄/BuOH at 100° led to no product formation due to the sensitivity of the expected product 53 against the reaction conditions. On the other hand, the acid-catalyzed rearrangement of the corresponding 3′-Cl derivative at 130° in aqueous H₂SO₄ in ethylene glycol led to the formation of 1,2,3,4-tetrahydro-2,2-dimethylquinolin-4-on ( 54 ; cf. Scheme 10), the hydrolysis product of the expected 4-chloro-1,2-dihydro-2,2-dimethylquinoline ( 56 ). Similarly, the acid-catalyzed rearrangement of N-(3′-bromo-1′-methylprop-2′-ynyl)-2,6-diisopropylaniline ( 37 ; cf. Scheme 21) yielded, by loss of one i-Pr group, 1,2,3,4-tetrahydro-8-isopropyl-2-methylquinolin-4-one ( 59 ).     

An efficient [4 + 2 + 1] entry to seven-membered rings

A new nickel-catalyzed procedure for the [4 + 2 + 1] cycloaddition of trimethylsilyl diazomethane with alkynes tethered to dienes has been developed. A broad range of unsaturated substrates participate in the sequence, and stereoselectivities are generally excellent. Three possible mechanisms are proposed, and each involves the generation of a transient nickel carbene species.     

Rhodium catalysed [2+2+2] cycloadditions- an efficient regiospecific route to calomelanolactone

A short regiospecific synthesis of calomelanolactone has been devised in which the key step is a [2+2+2] cycloaddition.