Methyl propiolate spectrum

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. " °... 

To correlate the structural features of a specific copper or cuprate reagent with its reactivity, a better understanding of the interaction of such species with metal halides, ligands, solvents, and, last but not least, substrates is required. Such investigations have already begun and seem to have a promising future. In an elegant NMR study by Krause et al. [23] it was demonstrated that the reaction between t-BuCu(CN)Li and methyl propiolate (see Scheme 1.25) could be monitored by NMR. At -100 C, resonances attributable to the presence of a complex between the oi anocuprate and the substrate were observed. After the temperature had been raised to -40 C, the NMR spectrum of a vinylcopper intermediate... 

The reaction between secondary enediamines and propiolic acid esters has been studied in detaiP. In aprotic solvents such as benzene and dioxane, 8 adds to methyl propiolate at ambient temperature to give almost quantitatively product 118 with a tron -configuration of the new double bond, as indicated by a Jhh coupling constant of around 16 Hz in the NMR spectrum. It appears that the reaction proceeds via an ene-addition mechanism. In refluxing ethanol, the C-adducts 118 are converted to the heterocyclic compounds 119. The direct transformation of 8 to 119 is easily achieved in alcoholic solvents. 1,1-Enediamines with jS-nitro, ester and acetyl substituents undergo analogous addition and cyclocondensation reactions to give heterocyclic compounds jj5(39,i2o A -Ethynylcarbonyl imidazole behaves similarly to propiolic acid esters ° (equation 41). 

C (10 mmHg). In CeD, the PNMR shift was <5 +159, entirely consistent with the presence of a C=P double bond, and this was confirmed by the C NMR spectrum, which showed phosphorus to be directly coupled to an sp carbon (<5 194.7, Jfc 68.7 Hz) and to an sp carbon 37.1, /pc 51.4 Hz). The 27f-phospholes where the 2-phenyl was replaced by 2,4,6-trimethylphenyl, 2,4,6-trimethoxyphenyl, and methyl were also made in good yield by this method. These 2 -phospholes are thermally stable but very sensitive to water and were hydrated on attempted chromatography on Kieselgel to form the phospholanone (204). Other reactions observed (Scheme 46) included a Diels-Alder cycloaddition with methyl propiolate (giving (205)), and a 1,3-dipolar cycloaddition with mesityl nitrile oxide that formed (206). 

As is true for hydrostannation, acetylenes are also more reactive than the olefins toward hydroplumbation. Acetylenedicarboxylic acid dimethyl ester and ethyl propiolate 152) add Bu3PbH at — 50° C (used as a pure substance, or made in situ from organotin hydrides) spontaneously and without side reactions. Me3PbH adds in the same smooth manner to cyanoacetylene and methyl propiolate 165). Phenylacetylene reacts under the same conditions but in a side reaction Pb is precipitated and H2 evolves. After a short while starting materials disappear if excess of lead hydride is used. The IR spectrum shows absorption at 990 cm , which is in accordance with a trans adduct 152,194). 

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