New synthetic method for indole-2-carboxylate and its application to the total synthesis of duocarmycin SA

The sequential coupling and cyclization reactions between aryl halides and methyl propiolate were investigated. The electron-withdrawing groups on the aromatic ring are essential for producing the methyl indole-2-carboxylate derivatives. On the other hand, the presence of an extra methyl propiolate and Pd(PPh3)4 were required to provide an efficient catalytic system for the cyclization reactions. This reaction was used for the total synthesis of duocarmycin SA.     

Synthesis of hexahydro[1,4]diazocino[7,8,1-<Emphasis Type="Italic">jk</Emphasis>]carbazoles and 1-methoxy-9-(β-vinylethylamino)ethylcarbazoles

3-Ethylhexahydropyrazino[3,2,1-jk]carbazole is converted into hexahydro[1,4]diazocino[7,8,1-jk]carbazoles by the action of methyl propiolate and acetylacetylene in acetonitrile and into 1-methoxy9-(β-vinylethylamino)ethylcarbazoles by the action of acetylenedicarboxylic ester and methyl propiolate in methanol. 3-Benzyl-substituted pyrazinocarbazole does not react with alkynes.     

Thiohydrazides and acetylene esters,A new route to 1,3,4-thiadiazoles

Aromatic thiohydrazides react with dimethyl acetylenedicarboxylate or methyl propiolate to yield carbomethoxymethyl-substituted 1,3,4-thiadiazoles. In a 2:1 ratio of methyl propiolate to aromatic thiohydrazide, 1,3,4-thiadiazoles with acrylate ester side chains are formed.     

The Diels-Alder Reaction of Dienes Derived from Substituted 3-(Phenyl-Thio)-3-Sulfolenes

Substituted 3-(phenylthio)-3-sulfolenes (3) and (4) are good precursors for 2-(phenylthio)-1,3-butadienes (5) and (6). The Diels-Alder reaction of the dienes derived from (3) and (4) with various dienophiles was studied. It was found that heating of sulfolenes (3) with methyl propiolate and N-phenylmaleimide afforded the Diels-Alder adducts of (5) directly and with complete regio- and stereospecificity. The same reaction with methyl vinyl ketone gave a mixture of endo and exo addition products. If sulfolenes (3) were first converted to the dienes (5) using lithium aluminum hydride and then reacted with methyl vinyl ketone in the presence of anhydrous zinc chloride, the stereoselectivity could be improved. Sulfolenes (4) also underwent cycloreversion/cycloaddition with methyl acrylate, methyl vinyl ketone, and N-phenylmaleimide, but gave mostly the double bond-isomerized cycloaddition products. The regiochemistry of cycloaddition was delicately dependent on the dienophiles used.     

Activation of a 1,10-phenanthroline ligand on a rhenium tricarbonyl complex

The reactions of complex [Re(PPh(2))(CO)(3)(phen)] with either methyl acrylate or methyl propiolate afford products in which the phen ligand has been activated.     

Stereoselective 1,3-dipolar cycloadditions of a chiral nitrone derived from erythrulose. An experimental and DFT theoretical study

We have investigated several 1,3-dipolar cycloadditions of a chiral nitrone prepared from L-erythrulose. While cycloadditions to carbon-carbon multiple bonds of dipolarophiles such as ethyl acrylate, ethyl propiolate, or dimethyl acetylenedicarboxylate were poorly stereoselective, reaction with acrylonitrile provided predominantly one diastereomeric adduct. Furthermore, the regioselectivity exhibited by the two structurally similar dipolarophiles ethyl acrylate and ethyl propiolate was found to be opposite. The molecular mechanisms of these cycloadditions have thus been investigated by means of density functional theory (DFT) methods with the B3LYP functional and the 6-31G and 6-31+G basis sets. A simplified achiral version of nitrone 1 as the dipole, and methyl propiolate or acrylonitrile as the dipolarophiles, were chosen as computational models. The cycloadditions have been shown to take place through one-step pathways in which the C-C and C-O sigma bonds are formed in a nonsynchronous way. For the reaction with methyl propiolate, DFT calculations predict the experimentally observed meta regioselectivity. For the reaction with acrylonitrile, however, the predicted regioselectivity has been found to depend on the computational level used. The calculations further indicate the exo approach to be energetically favored in the case of the latter dipolarophile, in agreement with experimental findings. The main reason for this is the steric repulsion between the nitrile function and one of the methyl groups on the nitrone that progressively develops in the alternative endo approach.     

The optimization for cyclization reaction of 2-(2-carbomethoxyethynyl)aniline derivatives and formal synthesis of pyrroloquinoline quinone and its analogue utilizing a sequential coupling-cyclization reaction

The reaction conditions for the Pd-catalyzed cyclization reaction of 2-(2-carbomethoxyethynyl)aniline derivatives were investigated. The amounts of Pd(PPh₃)₄, methyl propiolate, and ZnBr₂ could be significantly reduced compared with those reported in our preliminary publication by careful tuning of the solvent and the reaction temperature. In addition to the above results, formal syntheses of pyrroloquinoline quinone (PQQ) and its analogue from 2-amino-5-nitrophenol using a Pd-complex-catalyzed sequential coupling-cyclization reaction between methyl propiolate and 2-iodoaniline derivatives are described.     

A novel polyaddition of bifunctional acetylenes containing electron-withdrawing groups. III. Synthesis of polymers having β-alkoxyenoate moieties by the reaction of internal diynes with diols

Tri-n-butylphosphine-catalyzed polyadditions of activated internal diynes (bifunctional β-substituted propiolate, 1B and 1C ) with diols are described. Although a terminal bispropiolate ( 1A ) could not produce soluble polymers, with secondary diols, the polyaddition of 1B or 1C with primary as well as secondary diols gave corresponding polymers ( 3 , only composed of E isomeric units) in high yield. The rate of the present polyaddition was estimated by a model reaction of benzyl alcohol with methyl 2-heptynoate ( 4 ), from which the introduction of alkyl groups at the β-position of propiolate moieties was found to decrease the rate of the reaction by 80 times. Furthermore, the rate-determining step on this polymerization system was speculated to be a protonation step of zwitterionic intermediates with protons from diols. © 1996 John Wiley & Sons, Inc.     

1,3-Dipolar cycloaddition reactions of 3-acylimino-1-methylbenzimidazolium betaines

3-Acylimino-1-methylbenzimidazolium betaines undergo 1,3-dipolar cycloaddition reactions with activated alkenes (methyl acrylate, acrylonitrile, and fumaronitrile) and methyl propiolate to produce 2-substituted 1-methylbenzimidazoles. The transformation involves the initial formation of a 1,3-dipolar cycloadduct followed by the N? N bond cleavage. The primary adducts can be isolated from the reaction with methyl acrylate and acrylonitrile.     

Studies on the synthesis and biosynthesis of the fungal alkaloid necatorone

An alternative pathway for the biosynthesis of the fungal alkaloid necatorone has been studied using fluorine-labeled 3-(2-carboxyphenylamino)-l-tyrosine. Although no incorporation of this compound could be detected in feeding experiments with young specimens of Lactarius necator, an analogous 3-aminotyrosine derivative could be converted synthetically into the oxopyridoacridine core structure of necatorone. In experiments aimed at the synthesis of aaptamine-type alkaloids, an unprecedented cyclization of a 3-aminotyrosine-methyl propiolate adduct to a methyl isoquinoline-3-carboxylate was observed. A mechanism is proposed, in which C3 of the propiolate delivers C1 of the isoquinoline nucleus.     

Synthesis and michael reaction of 3,4-dimethylpyrrole

A two step synthesis of 3,4-dimethylpyrrole via the reduction of 3-carboethoxy-4-methyl-pyrrole is described. Michael addition of methyl vinyl ketone and butyn-2-one to 3,4-dimethylpyrrole gives the bisadducts, 2,5-bis(3-oxobutyl)-3,4-dimethylpyrrole and 2,5-bis(3-oxobutenyl)-3,4-dimethylpyrrole, respectively, while ethyl propiolate affords only the monoadduct, ethyl 3-(3,4-dimethylpyrrol-2-yl)propenoate. Catalytic reduction of the latter ester gives ethyl 3-(3,4-dimethylpyrrol-2-yl)propanoate which with ethyl propiolate gives ethyl 3-(5-carbethoxyethyl-3,4-dimethyl-2-yl)propenoate.     

Regioselective hydrosilylations of propiolate esters with tris(trimethylsilyl)silane

Lewis acid and substituent dependency on the regioselectivity of hydrosilylation of propiolate esters 1a-c with tris(trimethylsilyl)silane (2a) was found. The reaction of methyl and ethyl propiolate esters and 2a without Lewis acid and in the presence of EtAlCl2 and Et2AlCl gave beta-silicon-substituted Z-alkenes 3 selectively. On the other hand, reaction in the presence of AlCl3 in dichloromethane gave alpha-silicon-substituted alkenes 4. In the case of trifluoroethyl propiolate ester 1c, reaction with aluminum chloride-based Lewis acids gave alpha-silicon-substituted alkenes 4 exclusively. Two competitive mechanisms, free-radical and ionic, are proposed as the source of the complementary regioselectivity displayed in these reactions. A transition state of the radical-forming step was obtained computationally. The reaction of various reactive acetylene substrates and 2a without Lewis acid and without solvent at room temperature gave beta-silicon-substituted Z-alkenes 3 selectively.     

Formation of benzofuran and 2H-chromene structures in one reaction. A novel synthesis of 2H-chromene derivatives

Heating the morpholinal of nitrosalicylic aldehyde with methyl propiolate in acetonitrile in the presence of Cul affords an equimolar mixture of 2-methoxycarbonylmethyl-3-morpholino-5-nitrobenzofuran and 3-methoxycarbonyl-2-morpholino-6-nitro-2H-chromene, the structures of which were determined by X-ray analysis. Only the 2H-chromene mentioned above was obtained in the absence of Cul and solvent.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1222–1228, May, 1996.     

Reaction of enehydrazines with acetylenecarboxylic esters

Eight products from reactions of acetylacetone-, methyl acetoacetate- and methyl formyacetate dimethylhydrazones with dimethyl acetylenedicarboxylate and methyl propiolate have been characterized by the usual spectroscopic methods and, partly, structure analyses.     

Reaction of 1,2‐Dialkyldiaziridines and 1,2,3‐Trialkyldiaziridines with Methyl Propiolate in Ionic Liquids and in Organic Solvents

An interaction of 1,2‐dialkyldiaziridine and 1,2,3‐trialkyldiaziridine with methyl propiolate was studied both in organic solvent (MeCN, CH₂Cl₂, C₆H₆) and in ionic liquids. Earlier unknown linear structures, in which three molecules of methyl propiolate were suited to one diaziridine molecule (adducts 1 : 3), were obtained in MeCN. The diaziridine ring expansion products 1,2,3,4‐tetrahydropyrimidine derivatives (adducts 1 : 2) and, along with them in some cases, the same linear structures were obtained in ionic liquids. A mechanism of reactions found was offered. The regioselectivity of reactions was supposed to determine by the structure of substituents in initial diaziridines. This conclusion was supported by quantum chemical calculations.     

Two directions in the heterocyclization of thiocarbamoylpyridinium(isoquinolinium)ylides in their interaction with esters of acetylenecarboxylic acids

It has been found that pyridinium- and isoquinoliniumthiocarbamoylazomethinylides react with esters of acetylenedicarboxylic and propiolic acids in two directions. The first direction is heterocyclization of the thioamide fragment of the ylide; under the influence of dimethyl acetylenedicarboxylate, a thiazolyl-4-one ring is formed, and by the interaction of the pyridiniumylide with methyl propiolate, a thiazin-4-one ring is formed. The second direction consists of annelation of the imidazole ring to the isoquinoline system upon reaction with methyl propiolate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1688–1691, December, 1993.     

Efficient synthesis of N-methoxyindoles via alkylative cycloaddition of nitrosoarenes with alkynes

[reaction: see text] N-Methoxyindoles are produced in moderate to excellent yields from the reaction between nitrosoarenes and alkynes in the presence of K2CO3/(CH3)2SO4. Terminal alkynes with conjugating substituents afford 3-substituted N-methoxyindoles exclusively. The analogous reactions with methyl propiolate provide a one-step preparation of phytoalexin analogues from Wasabi.     

An improved synthesis of pyrido[2,3-d]pyrimidines

An improved and efficient synthesis of 1,3-dialkylpyrido[2,3-d]pyrimidine-2,4-(1H,3H)-diones from 6-methylaminouracils and methyl propiolate or diethyl ethoxymethylenemalonate is described.     

Benzothiazinones by addition of o-Mercaptobenzamides to acetylene esters

The condensation of o-mercaptobenzamides with methyl acetylenedicarboxylate or methyl propiolate occurs with trans addition of the SH to the alkyne linkage. The resulting vinyl sulfide adducts can be ring closed to 1,3-benzothiazin-4-ones in excellent yield.     

First C-C bond formation in the Pauson-Khand reaction: Influence of carbon-carbon triple bond polarization on regiochemistry: A density functional theory study

The influence of carbon-carbon triple bond polarization on the regiochemistry of the Pauson-Khand reaction has been studied with the B3LYP functional. The regiochemistry determining step of this reaction, i.e., olefin insertion leading to cobaltacycle formation, has been examined with ethylene as the olefin and propyne, methyl 2-butynoate, and methyl propiolate as the acetylenes. From this study, it has been concluded that, in absence of overwhelming steric effects of an acetylene substituent, the regiochemistry is influenced by the polarization of the acetylenic bond, which arises from the different substituents. The initial C-C bond is preferentially formed with the acetylenic carbon that has the greater electron density: with propyne, this leads to a cyclopentenone having the methyl group in the α-position; with methyl 2-butynoate, to a cyclopentenone with the CO₂Me in the β-position; with methyl propiolate, which is virtually unpolarized in the complex, to a cyclopentenone with the CO₂Me in the α-position (a result of steric effects). These theoretical results are concordant with those observed experimentally with norbornene. The question of axial versus equatorial reactive positions for the coordinated olefin is also addressed and a kinetic simulation is presented.