Tetrakis cyclobutene

Dispiro[2.2.2.0]octane 22 was obtained in good yield along with a fragmentation product 23 by treating 1,1,2,2-tetrakis-bromomethyl-cyclobutane 21 with zinc dust in aqueous ethanol4g). The cyclobutene analog of 22 has also been reported 4h). 

Photocycloaddition of oxygen heterocycles to alkynes has been of some use in the preparation of cyclobutene derivatives.279 Irradiation of tetrakis(trifluoromethyl)furan (336) and dimethylacetylene, for example, affords the adduct (337), which on further irradiation, is converted to the... 

Pentacarbonyl-(trifluor-chlor-athyl)- 1428 Pentacarbonyl-[5-triphenylstannyl-tetrakis-[trifulor-methyl]-cyclobuten-(2)-yl - 1429... 

Dewar thiophenes are thiiranes fused to cyclobutene rings. While the reversion of the tetrakis(trifluoromethyl) derivative to the normal thiophene structure requires a high temperature (r 1/2 160 , C Hg] 5.1 hr), the transformation can be achieved at room temperature by phosphines (86) such as Ph3P. A 1 1 adduct can be isolated when PhjPCl is added to the Dewar thiophene. However, the harder PhPCl2 and PCI3 and pentacovalent phosphorus compounds are totally ineffective for the isomerization. 

A number of approaches to tetrakis(trifluoromethyl)-pyrroles was developed using tetrakis(trifluoro-methyl)-Dewar-thiophene (183) [71]. The 1,3-dipolar cycloaddition with azides led to the tricyclic thiiranes 184. Subsequent desulfurization by treatment with PPha afforded the cyclobutenes 185 in good to quantitative yields. The result of thermolysis of 185 was strongly depended on the substituent on the amine nitrogen. Pyrroles 188 were formed in high yields (cases a and d), while only cyclopropene 189, or a mixture of 188 and 189 (cases b and c) were isolated. Pyrrole 188a was also synthesized by the reaction of 183 with aniline in 19 % yield [72]. 

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