Acetylene dicarboxylic esters

The Diels-Alder Reaction consists in the direct combination of a compound containing a conjugated diene system u ith a reagent which possesses a double or triple bond activated bj suitable adjacent groups. Examples of such reagents are maleic anhydride, p-benzoquinone, acraldehyde and acetylene dicarboxylic esters. Combination always occurs at the 1,4 positions of the diene system ... 

Reversible interaction of the carbonyl group with an azine lone-pair (cf. 245) should facilitate substitution adjacent to the heteroatom by the anion of a )3-hydroxyethyl ketone. A similar cyclic intermediate (246) is presumably responsible for the cyclization of acetylene dicarboxylic esters with azines. Similar cyclic intermediates... 

For the ordinary Diels-Alder reaction the dienophile preferentially is of the electron-poor type electron-withdrawing substituents have a rate enhancing effect. Ethylene and simple alkenes are less reactive. Substituent Z in 2 can be e.g. CHO, COR, COOH, COOR, CN, Ar, NO2, halogen, C=C. Good dienophiles are for example maleic anhydride, acrolein, acrylonitrile, dehydrobenzene, tetracya-noethylene (TCNE), acetylene dicarboxylic esters. The diene preferentially is of the electron-rich type thus it should not bear an electron-withdrawing substituent. 

Triphenylphosphine gives Michael additions to the activated triple bond of acetylene dicarboxylic esters in presence of acidic compounds HY (Scheme 1). The reactions take place easily at room temperature, even at -10°C [1], through formation of intermediate activated vinylic phosphonium salts, which undergo a subsequent Michael addition of HY. The reactions afford various stabilized ylides which can be isolated in high yields or undergo possibly evolution, for example by intramolecular Wittig reaction [2]. 

A related preparation of specific stabilized phosphonium yUdes corresponds to the reaction of triarylphosphines with acetylene dicarboxylic esters in presence of fullerene, which affords a cyclopropanyl-fullerene substituted stabilized phosphonium ylide [9] or the corresponding evolution products [10]. 

Synthetic routes to the title ring system using two other reagents, acetylene dicarboxylic ester and 2,4-dinitro-chlorobenzene, are shown in Scheme 28. Reaction of 145 with DMAD (or its ethyl analogue) yields a ring-closed... 

Acetylene dicarboxylic esters and (less easily) acetylene monocarboxylic esters replace nitriles from the 4,5-positions of 1,2,4,3-triazaphosphole rings (92) to give carboxyl derivatives of 1,2,3-diazaphospholes, presumably by a cycloaddition/cycloreversion mechanism, R/R = Me/Ph, SiMej/NMCj <83ZN(B)1484>. 

The products from l,3,2-diazasilacyclopent-4-enes (107 R = Bu , 2,6-Mc2C6H4) and TCNE or acetylene dicarboxylic esters result from cleavage of initial (2- -2) cycloadducts which are isolable in the case of (107 R = Bu ) and the acetylenic ester <87CB795>. 

Scheme 43 shows the details of the different steps involved in the equilibrium. The nucleophilic attack of the P(III) derivative on the acetylenic bond yields a 1,3-dipole which, after a fast protonation, frees aZ ion. If the subsequent addition of this ion occurs on the P atom (reaction a), a P(V) phosphorane is formed, but the addition of Z on the ethylenic C atom (reaction b) results in the formation of an ylide. Both of these reactions occur under kinetic control and, in both cases, X is always an OR group from the initial acetylene dicarboxylic ester. When the acetylenic compound is a diketone and X is an alkyl or aryl moiety, the C=0 group is much more electrophilic and the attack by the Z ion produces an alcoholate (reaction c), a new intermediate which can cyclize on to the P+ to form a phosphorane, or attack the a-C atom to form an ylide as in Scheme 42. Hence, reactions a and c can coexist, and are strongly dependent on the nature of the trapping reagent and of the P compound, but reaction b is blocked, whatever the reagent. This is well illustrated by the reaction of the 2-methoxytetramethylphospholane 147 on diben-zoylacetylene in the presence of methanol as trapping reagent. The proportions of the vinylphosphorane 157 and spirophosphorane 158 formed (Figure 24) are 13% and 84%, respectively.

Several cycloaddition reactions of 2,5-dihydrothiophene derivatives have been reported. Compounds possessing an enamine system undergo [2 + 2] cycloaddition with acetylene-dicarboxylic ester (Scheme 215) (77AHC(2l)253). Diels-Alder addition of the 2,5-di-hydrothiophene-3-carboxylic ester (557) with butadiene, followed by desulfurization, leads to the trisubstituted cyclohexane (558) (B-74MI31404). 

The Addition of the NH-Gtroup ofPyrazoles to Activated Double Bonds Pyrazoles undergo Michael addition to a,j3-unsaturated acids and esters,618,736,737,737 acrylonitrile,104,483,738 maleic anhydride, acetylene dicarboxylic ester,282,737 a,j8-unsaturated ketones,736 and quinones.104 Alkaline catalysts667 are not essential in this reaction,104 at least for addition to unsaturated nitriles, maleic anhydride, and quinones. The reaction is reversible, and V-pyrazolyl propionic... 

The rule that furans with substituents which show a -M effect cannot react as diene compounds does not hold with highly active dienophiles. Compounds in this category are acetylene dicarboxylic ester, and particularly dicyanoacetylene. 

The 1,4-diphospha-l,3-butadienes are suitable as ligands for cr-coordi-nated complexes with transition metals. Attempts to carry out pericy-clic reactions with maleinic anhydride, acetylene dicarboxylate esters, dimethylbutadiene, or cyclopentadiene failed, but Diels-Alder reactions with norbornadienes were successful (94). Earlier attempts to synthesize 1,4-diphosphabuta-l,3-dienes with oxalychloride and phenyl-bis(silyl)phosphane proceeded via ring closure [Eq. (42)] (89), where R = Ph (a) or [Pg.285]

Other systems Additions of perfluoro-2-butyne [143] and acetylene dicarboxylic ester [139] to perfluoro-aromatics will also occur (see Table 9.9 and Chapter 7, Section lllB). The extending anion may be trapped, and the more reactive the aromatic compound used, the more effective the competition with polymer formation (Figure 9.57) [144]. 

Besides processes (1) and (2), the reader should be aware that nucleophilic attacks on alkynes are treated in other chapters of this book, dealing with rearrangements, cyclizations, polyacetylenes, cyclic acetylenes and perhaps others. A number of publications overlap with ours in different ways and at different levels -. They treat individual alkynes or families " , e.g. acetylene, diacetylenes , acetylene dicarboxylic esters haloacetylenes , alkynyl ethers and thioethers > ynamines , fluoro-alkynes ethynyl ketpnes , nitroalkynes , etc. synthetic targets, e.g. pyrazoles , if-l,2,3-triazoles , isothiazoles , indolizines S etc. reagents, e.g. nitrones , lithium aluminium hydride , heterocyclic A -oxides - , azomethine ylids - , tertiary phosphorus compounds , miscellaneous dipolar nucleophiles - , etc. The reader will appreciate that all of these constitute alternate entries into our subject. 

Since thiol additions may be initiated readily by radicals this is always a complication to process (1). In the absence of controlled reaction conditions, the resulting regio and/or syn-anti selectivity as well as the reactivity could differ from what one expects from nucleophilic attack. For example, the usually reactive acetylene-dicarboxylic ester reacts more slowly with FjCcSH than does PhC=CR (R = H or... 

The steric course of additions of amines and alcohols to acetylene dicarboxylic ester was studied under various conditions. Secondary amines gave stereospecifically cis addition product. Nitrosyl formate can be generated in situ in the presence of an olefin to yield the nitrosoformate which on hydrolysis affords the hydroxynitroso compound in high yield. Transoximination gave the a-hydroxy ketone. Phosphorous tribromide can be added to olefins to yield 1 1 adducts with uv irradiation, peroxides, or heat as initiators ... 

For a reverse electron-demand Diels-Alder with azadienes, Barluenga8 reacted stable silylated imines 65 of unenolisable aldehydes (R = Ar or cinnamyl) with acetylene dicarboxylic esters to give the 2-azadienes 67. 

Unsubstituted pyridine, quinoline, and isoquinoline A-imines are the most reactive of all A-imines. They add to nitriles,1013 72-140 141 acetylene-dicarboxylic ester,75 139 142 propiolonitrile,143 propiolic esters,144 and carbon disfulfide.139 Dehydrogenation to a completely aromatic product, subsequent to the addition step, [see Eq. (15)] exerts an essential influence on the course of the reaction. 

A further type of degradation occurs during the photolysis or thermolysis of derivatives of the 2,3-oxaphosphabicyclo[2.2.2]octene system, formally derivatives of cyclic phos-phonic or phosphinic acids. The compounds 42 are obtained by Baeyer-Villiger oxidations, with 3-chloroperoxybenzoic acid, of the 1 1 adducts from monomeric l//-phospho-les and iV-phenylmaleimide, and 43 by the identical oxidation of the products of dimerization of monomeric but unstable li/-phospholes. The simpler substrates 44, similarly obtained by the oxidation of the Diels-Alder adducts prepared from acetylene dicarboxylic ester, have also been examined. The thermolysis (at 80-110 °C in toluene) or... 

The reaction of bicyclic phosphoramidites with alcohols offers a simple route to hydridophosphoranes. In particular the oxidative addition of a variety of alcohols (ROH) or phenol (PhOH) with bicyclic phosphoramidites of type (107) give a wide range of bicyclic phosphoranes of type (108) with the P-H bond in an equatorial position. A number of addition reactions with activated double (e.g. fumaric ester) and triple (e.g. acetylene dicarboxylic ester) bonds arc also dcscribcd. The reaction of hydridophosphoranes (109) with alcohols (1 lOa-0 takes a further step in the presence of diphenyl disulphide to generate the alkoxylated products (llla-f). ... 

Comparing the acetylene dicarboxylic ester with the fumaric ester, a slightly higher reactivity of the C=C over the C=C dienophile is noted. The efficiency of C=C and C=N bonds as dienophiles was compared by studying the reaction of butadiene with acrylonitrile mainly cyanocyclohexene and no vinyl-pyridine was found in the product, proving that the C=C bond is far more reactive than the C=N bond, at least in the homogeneous gas-phase reaction (heterogeneous catalysts lower the reactivity ratio to ca. 10) . 

Table 13 offers also the opportunity of a comparison of olefins and acetylenes as dipolarophiles. In some cases the C=C dipolarophile is more effective, for instance styrene appears more reactive than phenylacetylene in other cases the contrary is true, for instance acetylene dicarboxylic ester reacts faster than fumaric ester. When C=C and C N dipolarophiles were compared, the former were found to be more reactive for instance with diphenylnitrili-mine (in benzene, 80°C) phenylacetylene reacts 18 times as rapidly as benzo-nitrile . Nitriles also are less efficient than acetylenes as dienophiles (Section 4.1.3). 

Acidic hydrolysis of the reactive enamide led to the corresponding carboxylic acids 14 whereas alcoholysis gave esters 16 and aminolysis amides 15. The mechanism of the hydrolysis was shown to proceed via miinchnone derivatives 20 which, instead of being opened with a nucleophile, reacted as a 1,3-dipole in [3+2] cycloaddition reactions with propiolic esters or acetylene dicarboxylic esters to give after elimination of carbon dioxide protected pyrroles 19 (Scheme 3.2.4)... 

The Diels-Alder Reaction essentially consists in the direct combination of a compound possessing a conjugated diene system with a reagent that contains either a double-bond or a triple-bond, usually activated by conjugation with additional multiply-bonded systems, such as cyano, carbonyl, nitro, phenyl functions. It ultimately adds on to the 1, 4-positions of a conjugated diene system e.g., buta-1, 3-diene) with the formation of a 6-membered ring. Importantly, the ethylenic (double-bond) or acetylenic (tripple-bond) compormd is normally termed as the dienophile, the second reactant as the diene and the final desired product as the adduct. A few typical examples of such reagents are, namely maleic anhydride, para-benzoquinone, acetaldehyde and acetylene dicarboxylic esters. 

The kinetically controlled product of condensation of t-butyl isocyanide with acetylene dicarboxylic ester has been shown to have the bicyclobutane structure... 

This reaction can also be regarded as a Michael addition of pyrrole to maleic anhydride. Some N-substituted pyrroles, however, undergo a (4 + 2)-cycloaddition with acetylene dienophiles, for example, l-(ethoxycarbonyl)pyrrole with acetylene dicarboxylic ester ( 30) [108] ... 

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