Cyclopropenium Compounds

Dimethyl ditellurium, but not diphenyl ditellurium, reacted with trichlorocyclopropenium salts6 or with tetrabromocyclopropene7 to give tris[methyltelluro]cyclopropenium compounds. 

II. Molecular Design of Heteroatom-Substituted Cyclopropenium Compounds. 49... 

The cyclopropenium ion system (3C2jt), being the characteristic framework of cyclopropenium compounds, is of interest from the theoretical viewpoints set out below. 

Since triphenylcyclopropenyl perchlorate was first synthesized by Breslow in 1957, a number of substituted cyclopropenium compounds as well as the parent cyclopropenium compound (1967) have been reported. 1 But for the triheteroatom-substituted cyclopropenium compounds, which seem to offer a good model for investigation of the physical and chemical properties of the perturbed cyclopropenium system by hetero-atoms, no compounds except the trihalocyclopropenium ion ) were known until 1968. Since the chemistry of tri-heteroatom-substituted cyclopropenium compounds has very recently been under investigation in our laboratory, some of our work will be described here. 

So, in order to get the triamino (or tri-heteroatom-substituted) cyclopropenium compound, we need a Sul or Sn2 type reaction of tetrachlorocyclopropene with amine (or nucleophile). The SnI type... 

It should be noted, that /)-nitrobenzenediazonium chloride is allowed to react with diaminocyclopropenthione 19) under Meerwein conditions to afford the heteroatom-substituted cyclopropenium compound (40) (Eq. 23). When the diaminochlorocyclopropenium ion is allowed to react with diaminocyclopropenthione, it gives a sulfur-bridged dication (4/), as is shown in Eq. 24. Since diaminocyclopropenthione is synthesized from the diaminochlorocyclopropenium ion, it can be said in view of this result that the dication 41) is obtained from 2 moles of diaminochlorocyclopropenium ion and 1 mol of sodium sulfide. 

In this review the chemistry of some new electron systems, heteroatom-substituted cyclopropenium compounds", is briefly described from the viewpoints of molecular design, synthesis, molecular and electronic structures, and reactions. In each, we have encountered unique problems which will eventually produce novel fruits. In this sense the chemistry of heteroatom-substituted cyclopropenium compounds might indeed furnish topics in current chemistry and also in prospective chemistry. 

Acknowledgments. Our work on the cyclopropenium compounds described above was supported by Grants from the Ministry of Education, Japan (including Grant for Scientic Research) and Mitsubishi Chemical Co., Tokyo, Japan. I would like to thank heartily many collaborators whose names appear in the References for their contributions to the work. 

DePuy, C. H. Stereochemistry and Reactivity in Cyclopropane Ring-Cleavage by Electrophiles. 40, 73. Cyclopropenium Compounds... 

As might be expected of salts, cyclopropenium compounds are insoluble in non-polar solvents such as ether, chloroform or benzene. 

The transfer of the carbyne ligand to a C = C bond was finally achieved by using symmetrically substituted electron-rich alkyne substrates. The cation 1 reacts with R2NC = CNR2 (R = Me, Et) to give cyclopropenium compounds (Scheme 6) which can be isolated as the BF4 salts in moderate yields. This reaction represents the first transfer of an electrophilic carbyne ligand to a C = C bond. 

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