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Gold-catalyzed oxidations of propargyl alcohols with nitrones by using a P(tBu)2(o-biphenyl)Au+ catalyst, afforded bicyclic annulation products from the Mannich reactions of gold enolates. The same reactions of propargyl amines with nitrones by using the same gold catalyst gave distinct oxoarylation products. Our DFT calculations indicate that oxidation of propargyl alcohols with nitrones by using electron-rich gold catalysts lead only to gold carbenes, which can generate gold enolates or oxoarylation intermediates with enolate species having a barrier smaller than that of oxoarylation species.

Kinugasa reactions hold potential for bioorthogonal chemistry in that the reagents can be biocompatible. Unlike other bioorthogonal reaction products, β-lactams are potentially reactive, which can be useful for synthesizing new biomaterials. A limiting factor for applications consists of slow reaction rates. Herein, we report an optimized aqueous copper(i)-catalyzed alkyne-nitrone cycloaddition involving rearrangement (CuANCR) with rate accelerations made possible by the use of surfactant micelles. We have investigated the factors that accelerate the aqueous CuANCR reaction and demonstrate enhanced modification of a model membrane-associated peptide. We discovered that lipids/surfactants and alkyne structure have a significant impact on the reaction rate, with biological lipids and electron-poor alkynes showing greater reactivity. These new findings have implications for the use of CuANCR for modifying integral membrane proteins as well as live cell labelling and other bioorthogonal applications.

Abstract: An eco-friendly and efficient synthesis of nitrones is presented by condensation of an equimolar amount of aldehydes and N-substituted hydroxylamine hydrochlorides in glycerol as a recyclable solvent-catalyst. This novel protocol provides rapid and mild access to a series of nitrone derivatives in good to excellent yields in the absence of catalyst and base. Graphic abstract: SYNOPSIS In this study, a base-free protocol by using glycerol as the solvent-catalyst was applied for an eco-friendly synthesis of nitrones from the condensation of aldehydes and N-substituted hydroxylaminehydrochlorides.[Figure not available: see fulltext.].

Chiral cyclic ureas (2-imidazolinones) were prepared by the reaction of nitrones and isocyanoacetate esters using a multicatalytic system that combines a bifunctional Br?nsted base-squaramide organocatalyst and Ag+ as a Lewis acid. The reaction could be achieved with a range of nitrones derived from aryl- and cycloalkylaldehydes with moderate diastereo- and good enantioselectivity. A plausible mechanism involving an initial formal [3 + 3] cycloaddition of the nitrone and isocyanoacetate ester, followed by rearrangement to an aminoisocyanate and cyclization to the imidazolinone, is proposed.

In the present study, pyrrolo-isoxazolidines 3(a-l) and 4(a-e), 4g, 4i, 4j have been synthesized by using the 1,3-dipolar cycloaddition reactions of nitrones 1(a-l) with ester substituted N-aryl maleimide (2b). These heterocycles have been obtained in cis and trans diastereomeric forms. The structures of newly synthesized heterocycles have been confirmed from their spectroscopic parameters such as IR,1H NMR,13C NMR and ESI-MS. The in vitro antimicrobial evaluation of these compounds were also investigated. Most of the prepared heterocycles showed significant antimicrobial properties. C3-phenyl substituted products exhibited the remarkable antibacterial behaviours while C3-thienyl/furyl substituted heterocycles proved themselves potent antifungal agents.

A new catalytic enantioselective tandem deoxygenation/aza-Diels-Alder reaction of nitrones with enecarbamates was serendipitously discovered in the presence of chiral copper(II) diphosphate complexes. This process affords a wide range of 4-aminotetrahydroquinolines in respectable yields under mild conditions with good to excellent ee values.

Trifluoromethyl vinyl sulfide, a potential building block for pharmaceutically and agrochemically relevant products, is prepared and used for the first time in high-pressure-mediated 1,3-dipolar cycloaddition reactions with nitrones to synthesize (trifluoromethyl)sulfanyl isoxazolidines.

The catalytic formation of gold enolates from alkynes, nitrones, and nucleophiles is described, and their Mannich reactions result in nucleophile-directed chemoselectivity through cooperative catalysis. For 1-alkyn-4-ols and 2-ethynylphenols, their gold-catalyzed nitrone oxidations afforded N-containing dihydrofuran-3(2H)-ones with syn selectivity. The mechanism involves the Mannich reactions of gold enolates with imines through an O-H-N hydrogen-bonding motif. For aryloxyethynes, their gold enolates react selectively with nitrones to deliver 3-alkylidenebenzofuran-2-ones, as controlled by a C-H-O hydrogen-bonding motif.

An efficient, copper-catalyzed [3+1+1] cycloaddition reaction was developed for the expedient synthesis of pharmacologically interesting polysubstituted pyrroles from easily available nitrones and α-acidic isocyanides. The given approach features a new mo

A simple method to transform sulfones into nitrones and therefore into the corresponding carbonyl derivatives has been developed. Some examples demonstrate that it is a new reliable and versatile reaction in the toolbox of sulfones that has great synthetic potential. NMR and computational studies were used to elucidate the mechanism.

A simple method to transform sulfones into nitrones and therefore into the corresponding carbonyl derivatives has been developed. Some examples demonstrate that it is a new reliable and versatile reaction in the toolbox of sulfones that has great synthetic potential. NMR and computational studies were used to elucidate the mechanism.

Abstract: Highly efficient, convenient, simple procedure and a highly chemoselective method has been described for the conversion of nitroarenes to their corresponding nitrone derivatives by employing SnCl2·2H2O and Na2CO3 in the grinding apparatus in solvent-free conditions. Biaryl nitrones can be achieved via the condensation of an aldehyde with an unstable arylhydroxylamine which is prepared in situ through the reduction of the corresponding nitro aromatic compound. Interestingly, the slow and nonselective reduction of nitroarene to arylhydroxylamine step was directed with the condensation of in situ-prepared arylhydroxylamine with aromatic aldehyde (second step). Moreover, this protocol was successfully used for preparation of valuable dinitrones from dialdehyde and nitro aromatic compounds. For dinitrone preparation, dialdehyde compounds were first synthesized by the reaction of salicylaldehyde and glycol derivatives. Then, dialdehydes were reacted with reduced nitro compounds in optimal conditions that we used for synthesis of biaryl nitrones. Graphical Abstract: [Figure not available: see fulltext.].

A chiral N,N′-dioxide/Co(BF4)2·6H2O complex catalytic system has been developed to efficiently catalyze the asymmetric 1,3-dipolar cycloaddition of nitrones with methyleneindolinones. The corresponding chiral multisubstituted spiroisoxazolidines with three contiguous quaternary-tertiary stereocenters were obtained in moderate to high yields with excellent dr and ee values (up to 97% yield, >19:1 dr and 98% ee).

A rhodium-catalyzed intermolecular coupling between arylnitrones and diazo compounds by C-H activation/[4 + 1] annulation with a C(N2)-C(acyl) bond cleavage is reported, and 2,3-disubstituted NH indoles are directly synthesized in up to a 94% yield. A variety of functional groups are applicable to this reaction to give the corresponding products with high selectivity. Compared to other previously reported Rh(III)-catalyzed synthesis of homologous series, this method is simpler, more general, and more efficient.

A novel and efficient PhI(OAc)2-promoted one-pot reaction of aromatic hydroxylamines, aldehydes, and TMSCN in the presence of BF3·Et2O is described. A wide variety of N-substituted benzimidazolones are obtained with satisfactory yields under mild reaction conditions. The method was proven to be efficient for the synthesis of benzimidazolone derivatives from readily available starting materials.

The highly enantioselective 1,3-dipolar cycloaddition of nitrones with α,β-unsaturated acylcarboxylates was realized for the first time by using a chiral bis(indano-oxazoline)-based Ni complex. The reaction proceeded smoothly under mild conditions and provided isoxazolidines with three contiguous stereocenters in high yields with excellent diastereoselectivities (>20:1 dr) and enantioselectivities (up to 99 % ee). The reaction was scaled up to the gram scale, and the products were readily transformed into γ-amino alcohols and other potentially bioactive compounds.

A highly enantioselective 1, 3-dipolar cycloaddition of nitrone with α, β-unsaturated acyl phosphonate was developed for the first time by using a chiral indane-bis(oxazoline)-copper(II) complex. The reaction proceeded smoothly under mild conditions to provide isoxazolidines with multi-stereocenters in good yields with high to excellent diastereo- (>20:1 dr) and enantioselectivities (up to 99% ee). The resulting products were readily converted to multi-functional isoxazolidines or γ-amino alcohol compounds.

The development of photoredox reactions of 1, 3- dipolar cycloaddition of nitrones with alkenes is reported. It offers an efficient synthetic method to obtain isoxazolidine derivatives under mild conditions in synthetically useful yields. The nitrones are cyclized with oxidizable styrenes and aliphatic alkenes via a polar radical crossover cycloaddition reaction through photocatalytic reaction without additives. In addition, bis(indole)methanes can also be prepared through this method.

The regio- and stereoselective control of cycloaddition reactions to polyconjugated systems has been demonstrated by applying asymmetric organocatalysis. Reaction of 2,4-dienals with nitrones allows for a highly regio- and stereoselective 1,3-dipolar cycl

The compounds N-(benzylidene)-anilines XArCH=NArY (XBAY), N-(phenyl-ethylene)-anilines XArC(CH3)=NArY (XPEAY) and N-phenyl-α-phenylnitrones XArCH=N(O)ArY (XPNY) have bridging group CH=N, C(CH3)=N and CH=N(O) respectively, in which the C(CH3)=N has a side-group methyl CH3 at carbon end and the CH=N(O) has a side-group O atom at nitrogen end. In this work, a series of XPEAY and XPNY were synthesized, and their longest wavelength maximum λmax (nm) of ultraviolet absorption spectra were measured. Then the change regularity of the νmax (cm-1, νmax=1/λmax) of XPEAY and XPNY were investigated, and they were compared with that of XBAY (reported by ref.26). The results indicate: (1) There are no good linear relationships between the νmax of XBAYs and XPEAYs or XPNYs. (2) In case of a same set of X-Y group couples, the distribution of λmax of XPEAYs is larger than that of XPNYs. (3) The side-group CH3 makes the effect of σ(X) larger than that of σ(Y) on the νmax of XPEAYs, whereas the O atom makes the effect of σ(Y) larger than that of σ(X) on the νmax of XPNYs. (4) The cross-interaction between X and Y has important effect on the all νmax. However, the cross-interaction between CH3 and X/Y has not important effect on the νmax of XPEAY, and the cross-interaction between O and X/Y has not important effect on the νmax of XPNY. Copyright

An iron-catalyzed intermolecular [4 + 2] cyclization of arylnitrones with geminal-substituted vinyl acetates was developed for the synthesis of 2,4-disubstituted quinolines in moderate to good yields with good functional group compatibilities. Preliminary mechanistic studies suggest a plausible iron-catalyzed C-H activation process under external-oxidant-free conditions.

Maleimide-terminated triethylene glycol thiolate monolayer-protected gold nanoparticles (Mal-EG4-AuNPs) with a core size of 2.5±0.7 nm were prepared. Mal-EG4-AuNPs were modified in high yields via interfacial 1,3-dipolar cycloadditio

The direct C-H annulation of anilines or related compounds with internal alkynes provides straightforward access to 2,3-disubstituted indole products. However, this transformation proceeds with poor regioselectivity in the synthesis of unsymmetrically 2,3-diaryl substituted indoles. Herein, we report the rhodium(III)-catalyzed C-H annulation of nitrones with symmetrical diaryl alkynes as an alternative method to prepare 2,3-diaryl-substituted N-unprotected indoles with two different aryl groups. One of the aryl substituents is derived from N?C-aryl ring of the nitrone and the other from the alkyne substrate, thus providing the indole products with exclusive regioselectivity.

The reactivity of metalated alkoxy-1,3-dienes and α-aryl-N-phenylnitrones in the presence of LIC-KOR base, equimolar mixture of alkyllithium (LIC) and potassium alcoxides (KOR), (Schlosser, 1994) [1] has been studied. A cascade reaction involving a E1cb p

Cycloaddition of C,N-diphenylnitrones 1 to N-aryl maleimides 2 afforded two diastereomeric isoxazolidines with high selectivity. The structure and steric configuration of the adducts have been assigned on the basis of 1H NMR, 1H NMR COSY, 13C NMR and IR spectroscopy. The π-π stacking interactions between maleimide's and nitrone's aromatic rings during the 1,3-dipolar cycloaddition were assumed to control the exo-endo selectivity of the reaction. Thus, the exo-endo ratio depends upon the position of the substituent present on the C-phenyl ring of the C,N-diphenylnitrones.

N-aryl-substituted nitrones were employed as fiveatom coupling partners in the rhodium-catalyzed cyclization with diynes. In this reaction, the nitrone moiety served as a directing group for the catalytic C-H activation of the N-aryl ring. This formal [2+2+5] approach allows rapid access to bridged eight-membered heterocycles with broad substrate scope. The results of this study may provide new insight into the chemistry of nitrones and find applications in the synthesis of other heterocycles,.

An umpolung approach toward nitrone construction utilizing a phosphine-mediated addition of 1,2-dicarbonyls to nitroso compounds is reported. The reaction exhibits a high degree of chemoselectivity and provides direct access to isoxazolidines, imines, and

Reaction of -aryl-N-phenyl nitrones with 3.methyl-1-phenyl-2-pyrazoline-5-one in the presence of a catalytic amount of silica tungstic acid in EtOH/H2O afforded, unexpectedly, high yields of bis(3-hydroxy-1-phenylpyrazolyl)-arylmethanes instead of the two possible 1,3-addition products. This is the first report of the synthesis of bis(3-hydroxy-1-phenylpyrazolyl)-arylmethanes via the reaction of nitrones and a pyrazolin-5-one. A possible mechanism for the process is suggested.

Highly functionalized oxazinanes are efficiently prepared through urea-catalyzed formal [3 + 3] cycloaddition reactions of nitrones and nitrocyclopropane carboxylates. The reaction system is general with respect to both the nitrocyclopropane carboxylates and nitrones enabling the preparation of a large family of oxazinanes, typically in high yield. This method affords access to enantioenriched oxazinane products through chirality transfer from enantioenriched nitrocyclopropane carboxylates.

Benzoxazolone pharmacophore is present in clinical pharmaceuticals, drug candidates, and many compounds having a wide spectrum of biological activities. The methods available for the synthesis of benzoxazolones have limited diversity due to problems in accessibility and air-sensitivity of diversely substituted o-aminophenols from which they are generally prepared by cyclocarbonylation with phosgene or its equivalents. The present paper describes a mild method for the synthesis of 3-alkylbenzoxazolones from easily accessible and air-stable nitroarenes. Nitroarenes were converted to N-alkyl-N-arylhydroxylamines in two steps involving partial reduction to arylhydroxylamines followed by selective N-alkylation. Treatment of N-alkyl-N-arylhydroxylamines with trichloroacetyl chloride and triethylamine afforded 3-alkylbenzoxazolones generally in good yields through an uninterrupted three-step sequence involving O-trichloroacetylation, N→Cortho trichloroacetoxy shift, and cyclization in a single pot at ambient temperatures. The present method is mild, wide in scope, economical, and regioselective. Many sensitive groups like alkyl and aryl esters, amide, cyano, and the carbon-carbon double bond survive the reaction.

Gold and silver: When allenyl acetals and nitrones are treated with a catalytic amount of a gold complex and a silver salt they react through a cyclization-cycloaddition cascade reaction to give a mixture of diastereomeric tricyclic products. The mixture converges to a single product upon acid hydrolysis (see scheme). The key intermediate is postulated to be a 1-methoxyfulvene species. Copyright

The present study was designed to synthesize and evaluate pyrrolo-isoxazole benzoic acid derivatives as potential acetylcholinesterase (AChE) inhibitors for the management of Alzheimer's disease. The synthesis of pyrrolo-isoxazole benzoic acid derivatives involved ring opening cyclization of p-aminobenzoic acid with maleic anhydride to yield maleanilic acid, which in turn afforded N-arylmaleimide via ring closed cyclization. Azomethine-N-oxides were obtained by condensation of N-arylhydroxylamine with differently substituted benzaldehydes followed by refluxing of N-arylmaleimide with differently substituted azomethine-N-oxides to pyrrolo-isoxazole benzoic acid derivatives as cis- and trans-stereoisomers. The synthesized compounds were evaluated in vitro for AChE inhibitory activity in rat brain homogenate with donepezil as standard AChE inhibitor. Thereafter, the most potent test compound was evaluated for in vitro butyrylcholinesterase inhibitory activity and in vivo memory evaluation in scopolamine (0.4 mg/kg)-induced amnesia in mice by employing Morris water maze test. All pyrrolo-isoxazole benzoic acid derivatives demonstrated potent AChE inhibitory activity. Most of compounds exhibited similar activity to donepezil and four of them (7h, 7i, 8i, and 8h, IC50 = 19.1 ± 1.9-17.5 ± 1.5 nM) displayed higher inhibitory activity as compared to donepezil (21.5 ± 3.2 nM) with compound 8ia (IC50 = 17.5 ± 1.5 nM) being the most active one. The test compound 8ia also ameliorated scopolamine-induced amnesia in mice in terms of restoration of time spent in target quadrant (TSTQ) and escape latency time (ELT). It may be concluded that pyrrolo-isoxazole benzoic acid derivatives may be employed as potential AChE inhibitors.

A series of 2,3-diphenyl-5-(naphthalen-1-yl)-4H-2,3,3a,5,6,6a- hexahydropyrrolo[3,4-d]isoxazole-4,6-dione derivatives were synthesized via 1,3-dipolar cycloaddition of azomethine N-oxides with N-(α-naphthyl) maleimide. The pyrrolo-isoxazole derivatives were assigned cis- and trans- configurations (3-A and 3-B) with respect to proton C3-H on azomethinic carbon on the basis of their 1H NMR. The reaction proceeds through cis- endo addition rule indicating the predominance of cis isomer. The cis- and trans- isomers of a prototype compound 3a i.e., compound 3a-A and compound 3a-B were evaluated for anti-stress activity in immobilization-induced acute stress. Compound 3a-A (5 and 10 mg/kg) and compound 3a-B (10 mg/kg) attenuated immobilization stress-induced behavioral alterations in Swiss albino mice suggesting that pyrrolo-isoxazole may serve as lead molecule for the development of anti-stress agents.

Enantioselective nitrone cycloadditions with 2-alkenoyl pyridine N-oxides as dipolarophiles have been reported. The reaction is catalyzed by Cu (II)-BOX complexes to give the expected isoxazolidine products with high diastereo-and enantioselectivity.

A novel one-pot azide-alkyne/ketenimine-nitrone cycloaddition sequence that is induced by copper(I) and allows the transformation of sulfonyl azides, alkynes, and nitrones to highly substituted imidazolidin-4-ones is described. The corresponding heterogeneous version utilizing Cu(I)-modified zeolites as recyclable heterogeneous catalysts shows marginally improved yield and diastereoselectivity.

Synthesis of a series of novel spiro-isoxazolidines has been accomplished in good yields by regio-and diastereoselective 1,3-dipolar cycloaddition of (E)-2-arylidene-(2H)-indan-1-ones 1a-d to C-aryl-N-phenylnitrones 2e-h. The structure of the spiro-adduct

Under mild microwave irradiation conditions and without any additional organic solvents, a large variety of nitrones were prepared in a weak Lewis base phosphinite task-specific ionic liquid (TSILOPPh2) in excellent yields. This catalytic TSIL was also re

Cycloaddition reaction of a series of synthesized aromatic nitrones with acrylonitrile (ACN) was studied in toluene and in microemulsions made of water/ACN/(sodium dodecylsulfate/n-butanol = 1/2). The phase diagram of the latter system was worked out and revealed a wide domain of microemulsions, particularly in the vicinity of the water-borne region. Of these microemulsions, the oil-rich ones (W/O) gave the best results in the cycloaddition reaction. In the conventional medium (toluene), the reaction afforded mixtures of four diastereoisomers of isoxazolidines in moderate overall yields (ca. 30-70 %). However, the reactions in microemulsions were featured with relatively milder conditions (lower temperatures and shorter reaction times) and better yields, 60-80 % after 6 h at 25 °C. Enhancement of the yields (80-100 %) was effected under the same reaction conditions, employing metal triflates Lewis acid catalysts in the microemulsion systems. A linear relationship between the temperature and the reaction time was found; a 25 °C rise in temperature led to a reaction time drop of about 90 % to achieve nearly the same yield.

A large variety of C-aryl and C-alkyl nitrones were synthesized within 0.5-15 min via the condensation of aldehydes with N-(methyl, phenyl, or t-butyl)hydroxylamines over MgO by hand-grinding with an agate mortar. These reactions were investigated under d

Micelle-promoted, copper-catalyzed multicomponent Kinugasa reactions were studied in aqueous media. Reactions were performed in a 'single pot' for a series of in situ generated C,N-diphenylnitrones with Cu(I) phenylacetylide providing β-lactams in yields of 45-85%. Substituents affect the reaction by either accelerating cycloaddition or minimizing side reactions.

Several novel benzimidazole-3-oxide-1-oxyl radicals with substituents at 5 and/or 6 position were synthesized. The ESR analysis of nitrogen hyperfine coupling constants (hfccs) revealed that substituents at 5 and 6-position affect the spin density to greater extent than substituents on the phenyl ring at 2-position. Density functional theory calculations of nitrogen hfccs were performed using several different Pople type basis sets, as well as double and triple zeta quality individual gauge for localized orbital (IGLO-II, IGLO-III) and electron paramagnetic resonance (EPR-II, EPR-II) basis sets. Experimental and theoretical hfccs are compared.

Microwave irradiation allows increasing the speed of several reactions and also offers the possibility of eliminating poisoning organic solvents. In this work we report the microwave-assisted neat synthesis of α-phenyl-tert-butylnitrone (PBN) and other alkyl and aryl nitrones and also the rapid synthesis of isoxazolidines resulting from 1,3-dipolar cycloaddition of nitrones to ethyl trans-crotonate.

Reactive nitrones can be generated directly in situ by an unusual reaction of nitrosobenzene with styrene. The Royal Society of Chemistry.

Herein we report the synthesis of a novel amino acid with orthogonal functionality to the natural amino acid side chains. Tyrosine was O-alkylated with a cyclic 5-membered α,β-unsaturated ketone ring (5). We have established that this amino acid analogue can undergo cycloaddition reactions in aqueous media with in situ generated nitrones. Nitrone formation occurred by micellar catalysis can undergo aqueous 1,3-dipolar cycloaddition reactions with the unnatural Tyr. We also performed a linear free energy analysis of the one pot bioconjugation reaction in water using cyclopentenone as a model for the Tyr analogue and seven different aryl nitrones. We found that the Hammett ρ value was -0.94, suggesting that the reaction occurs in a concerted fashion with a slight positive charge buildup in the transition state. The Hammett ρ value also suggests that the bioconjugation reaction is tolerant of different substituents and thus may be useful for introducing novel functionality into peptides and proteins containing the Tyr analogue 5. The aqueous 1,3-dipolar cycloaddition reactions, that use nitrones to trap the O-alkylated Tyr 5, establish a novel strategy for rapid, water compatible bioconjugation reactions.

C-Aryl-N-phenylnitrones have been prepared in very high yields from N-phenylhydroxylamine and aryl aldehydes using the microwave irradiation technique within a few minutes. The synthesis of a new series of nitrones, viz. the series of C-aryl-N-(4′-chlorop

Regio- and stereoselectivities in cycloadditions of nitrones to dipolarophiles bearing an allylic oxygen, which furnishes substituted-isoxazolidine analogs of the furanose ring of nucleosides, have been investigated. Although the obtained regioselectiviti

(Chemical Equation Presented) The cycloaddition of nitrones and enantiomerically pure cyclopropane-1,1-dicarboxylates is examined. Transfer of optical activity to the adduct is dictated by thermal reaction conditions and nature of cyclopropane substitutio

A variety of imines were oxidised with urea-hydrogen peroxide using iron(III) and manganese (III)- tetraphenylporphyrins [Fe(TPP)Cl], [Mn(TPP)Cl] and manganese (III)-octabromotetraphenyl porphyrin [Mn(TPPBr8)Cl] as catalysts. Experimental resul

A mild and facile reduction of nitroarene with aromatic aldehydes promoted by metallic samarium to C, N-diaryl nitrones in moderate yields has been developed.

The reactions of nitrones with terminal alkynes, catalysed by a range of HETPHOX ligands afforded β-lactams in moderate to good conversions with ees up to 55%. High levels of diastereoselectivity, dependent on the alkyne, were obtained. For example, the reaction is highly cis-diastereoselective with phenylacetylene (>9:1), while an unexpected reversal of diastereoselectivity is observed with the 3,5-trifluoromethyl phenylacetylene, which is highly trans selective (1:9) with an ee of 53%. The reaction scope with differently substituted nitrones and phenylacetylenes was also studied.