Nucleophilic Additions to Acetylenes

In acetonitrile, the nitrogen ylides (152) react with DMAD but the usual indolizinic products formed in other solvents are not observed. Instead the products are formulated as the ylides (153) and are obtained by a mechanism which is believed to involve an unusual 1,3-shift of the CO2R group.i s An analogous 1,3-ethoxycarbonyl migration accounts for the formation of (154) from the ylide (155) and DMAD. A-Vinyliminopyridinium ylides, (155), are readily available from pyridinium A-imines and activated vinyl halides 

An attempted cycloaddition of the mesoionic 1,3,4-thiadiazoles (156) with DMAD resulted in fragmentation of the mesoionic ring and formation of the thiophen (157) and an S -cyanothioimidate (158).  

3ff-Pyrrolizines and DMAD in boiling toluene yield the substituted pyrrolizines (161). The final step may be regarded as a 1,9-sigmatropic shift and has been shown to be intramolecular by deuterium labelling. Using an excess of DMAD, the 1 2 adduct (162) is formed.  

Pyridine 1-oxide and phenylpropiolonitrile give a rearranged 3-alkylated derivative (163) as the major product by a mechanism as yet unknown. Attempts to prepare pyrido[2,3-c ]pyrimidine derivatives by the reaction of various alkyl 6-aminouracils with DMAD led instead to (164).  

Other studies involving nucleophilic attack on acetylenes include the reaction of 1-alkylbenzotriazoles with DMAD a detailed examination of 

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Nucleophilic addition to acetylenic sulfoxides provides a,/ -ethylenic sulfoxides. Treatment of 181 with monoalkyl-copper afforded nearly quantitatively /J-alkylated a, / -ethylenic sulfoxides 182 through cis-addition to the triple bond. The reaction with lithium dimethylcuprate also afforded a similar adduct however, the reaction with lithium di-n-butylcuprate was found to give a small amount of ethyl n-butyl sulfoxide 183 besides the... 

Synthesis of Heterocycles through Nucleophilic Additions to Acetylenic Esters... 

Nucleophilic additions to acetylenic esters, synthesis of heterocycles through, 19, 299... 

Synthesis, of tetracyclic and penlacyclic condensed thiophene systems. 32, 127 Synthesis and reactions of l-azirines. 13, 45 Synthesis of heleroeycles through nucleophilic additions to acetylenic esters, 19, 279... 

George, M. V, Khetan, S. K., Gupta, R. K., Synthesis of Heterocycles through Nucleophilic Addition to Acetylenic Esters, 19, 279. 

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