Dimethyl acetylene

Reactivity of 2-Amino Selenazoles with Ethyl Propiolate (54) and Dimethyl Acetylene Dicarboxylate... 

Ethyl 3-anilinocrotonate (82) undergoes reaction with dimethyl acetylene-dicarboxylate (57) with the formation of two products, ethyl 5-anilino-3,4-dicarbomethoxy-trfl s,cM-2,4-hexadienoate (83) and ethyl 5-anilino-3,4-dicarbomethoxy-ci5, cw-2,4-hexadienoate (84). 

In the case of 1,3-diphenylisoindole (29), Diels-Alder addition with maleic anhydride is readily reversible, and the position of equilibrium is found to be markedly dependent on the solvent. In ether, for example, the expected adduet (117) is formed in 72% yield, whereas in aeetonitrile solution the adduet is almost completely dissociated to its components. Similarly, the addition product (118) of maleic anhydride and l,3-diphenyl-2-methjdi.soindole is found to be completely dissociated on warming in methanol. The Diels-Alder products (119 and 120) formed by the addition of dimethyl acetylene-dicarboxylate and benzyne respectively to 1,3-diphcnylisoindole, show no tendency to revert to starting materials. An attempt to extrude carbethoxynitrene by thermal and photochemical methods from (121), prepared from the adduct (120) by treatment with butyl-lithium followed by ethyl chloroform ate, was unsuccessful. 

Substituted 1-benzoxepins can be obtained by the cycloaddition of activated acetylenes to the benzofuran system. When 2-(Af-mcthylanilino)benzofurans is treated with dimethyl acetylene-dicarboxylate, substituted 1-benzoxepins 1 are obtained in reasonable yield.180,181 This reaction presumably involves a 2a,7b-dihydrocyclobuta[6]bcnzofuran as an intermediate (see Section 4.2).182... 

Iodine azide, generated in situ from an excess of sodium azide and iodine monochloride in acetonitrile, adds to ethyl l//-azepine-l-carboxylate at the C4 — C5 and C2 —C3 positions to yield a 10 1 mixture of the rw-diazidodihydro-l//-azepines 1 and 2, respectively.278 The as stereochemistry of the products is thought to be the result of initial trans addition of the iodine azide followed by an SN2 azido-deiodination. The diazides were isolated and their stereochemistry determined by conversion to their bis-l,3-dipolar cycloadducts with dimethyl acetylene-dicarboxylate. 

The length of the axial bond would be expected on all theories to be important. The barrier height does decline from ethane to methyl silane to methyl germane, but of course the bonded atoms are different. Unfortunately reliable values are not available for dimethyl mercury, dimethyl acetylene, and similar molecules with still longer bonds. An apparent exception is provided by methyl mercaptan and methyl alcohol. The latter, with the shorter axial bond, has the lower barrier. 

A = Acrylonitrile B = Benzoquinone C = Naphthoquinone D = 5,8-Quinolinequinone E = Methyl vinyl ketone F = Dimethyl acetylene dicarboxylate G = Methyl acrylate ... 

Af-Ethylhydrazino)quinoxaline 4-oxide (277, R = Et) and dimethyl acetylene-dicarboxylate gave dimethyl 1-ethyl-l,2-dihydropyridazino[3,4-/ ]quinoxa-line-3,4-dicarboxylate (278, R = Et) (EtOH, reflux, 3 h 77%) the 1-methyl homolog (278, R = Me) (70%) was made similarly. ... 

To avoid problems with the separation of regiomers, dimethyl acetylene dicarboxylate (DMAD) was chosen as a dienophile. The intermolecular Diels-Alder reactions were performed in refluxing dichlorobenzene (bp 132 °C), while the intramolecular reaction of alkyne tethered pyrazinone required a solvent with a higher boiling point (bromobenzene, bp 156 °C). In the case of 3-methoxy or 3-phenyl pyrazinones a mixture of pyridinones and pyridines was obtained, while for the alkyne tethered analogue only the di-hydrofuropyridinone was isolated as the single reaction product. 

Diels-Alder reaction between the Danishefsky triene 1659 and excess dimethyl-acetylene dicarboxylate or methylpropiolate in boiling benzene proceeds, via 1660 and 1661, with loss of trimethylsilanol 4, to give 1662 a and 1662b in 51 and 37% yield, respectively these are transsilylated with methanol to give 1663a and 1663b [40] (Scheme 10.18). 

The reaction of triphenylphosphine with an excess of dimethyl acetylene-dicarboxylate gives not only the phosph(v)ole (32) but also a cyclo-pentenylidenephosphorane (33). 

A. Preparation.—The first reverse Wittig olefin synthesis has been reported. Triphenylphosphine oxide and dicyanoacetylene at 160 °C gave the stable ylide (1 78%) the reaction was reversed at 300 °C. No comparable reaction was observed with a variety of other activated acetylenes but tri phenyl arsine oxide gave the corresponding stable arsoranes with dicyanoacetylene (— 70 °C), methyl propiolate, hexafluorobut-2-yne, dimethyl acetylene dicarboxylate, and ethyl phenylpropiolate (130 °C). 

For the formation of ylides from triphenylphosphine with dimethyl acetylene dicarboxylate and with halonitroalkenes see Chapter 1, Section 2. 

Some molecules are not rigid as they contain functional groups that have a certain orientational freedom. For example, dimethyl acetylene, CH3-CSC-CH3, in which the two methyl groups rotate with little hindrance, cannot be described by a specific geometry,... 

A few examples of vinylogous methylene cyclopropenes are known. Thus, in an interesting reaction mode the spirohexadiene 93, prepared from dimethyl acetylene... 

Reaction of the betaine 714 with dimethyl acetylene-dicarboxylate gave the cycloadduct 715 (77H281). 

Reaction of arylthioamides with dimethyl acetylene dicarboxylate (DMAD) yields 2-aryl-l,3-thiazolin-4-ones at room temperature in moderate yields (Scheme 15).36... 

The planar seven-membered CN3S3 ring was first obtained as the ester 100 (R=C02Me), which is a minor product of the reaction of S4N4 with dimethyl-acetylene dicarboxylate.252 The parent 1,3,5,2,4,6-trithiatriazepine 100 (R=H) is obtained by carefully heating the ester with aqueous HC1 followed by decarboxylation. 

The reactions of electrophilic alkynes, such as DMAD (dimethyl acetylene-dicarboxylate), with metal per- and poly-chalcogenido complexes have been exploited for the synthesis of homoleptic and heteroleptic 1,2-dithiolene,... 

Trost [10] discovered a palladium-catalyzed enyne metathesis during the course of his study on palladium-catalyzed enyne cyclization. Treatment of the 1,6-enyne 25 with palladacyclopentadiene (TCPT, 26a) in the presence of tri-o-tolyl-phophite and dimethyl acetylene dicarboxylate (DMAD) in dichloroethane at 60°C led to cycloadduct 27 and vinylcyclopentene 28 in 97% yield in a ratio of 1 to 1 (Eq. 10). The latter compound 28 is clearly the metathesis product. 

The mesoionic compound 41 was further used in a reaction with dimethyl acetylene dicarboxylate (DMAD) to produce a nine-membered cycloadduct 44 which is formed by a reaction cascade of double addition of the alkyne and transannular ring opening of the intermediate 43 (Scheme 7) <20030BC978>. 

The products of the reaction of the benzophosphole (170) with dimethyl acetylene-dicarboxylate include the ylide (171) and the benzodihydrophosphonin (172).15 ... 

The cathodic reduction of 2-bromo-2-nitropropane in the presence of dimethyl acetylene dicarboxylate leads to 5,5-dimethyl-2,3,4-trimethoxycarbonyl-5-hydropyrrole as the major product (64% yield) (Scheme 85) [125]. 

A rather different route to hexadentate ligands containing 3-hydroxy-2-p5rridinone units is based on the reaction of an appropriate pyrazinone with dimethyl acetylene dicarboxylate, which replaces one of the ring-nitrogen atoms by carbon (82). 

The 7-azaquadricyclane (77), like its precursor (12), shows evidence in the NMR spectrum of restricted rotation about the N-CO bond. All the 7-heteroquadricyclanes, 76-79, are thermolabile, and they rearrange very readily to the corresponding azepines (80) or oxepin (81). (In another instance the 7-oxabicyclo[4.1.0] valence-bond tautomer was obtained instead. ) In appropriate conditions the addition of acetylenic esters (methyl propiolate and dimethyl acetylene-dicarboxylate) competes successfully with the isomerization and gives the ca o-tricyclic adducts 82 or 83. " °... 

With one exception, naphthalen-l,4-imines with a double bond between C-2 and C-3 are not known to dissociate thermally by either possible retro-Diels-Alder pathway (the reverse of reactions described in Section III, A, 1 and 2), and the enthalpy requirements for the formation of a benzyne or an acylic acetylene are doubtless unfavorable. However, the mass spectra of compounds 93-99 reveal one important fragmentation of the molecular ions to be loss of dimethyl acetylene-dicarboxylate, and another fragmentation pathway involves the formation of nitrilium ions MeC=NR and PhC=NR from 93-95 and 96-99, respectively. ... 

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