Addition to 1,3-Dienes and 1,3-Dipoles

Cycloadditions.—Addition to, i-Dienes and 1,3-Dipoles. Cyclopropenes have proved to be viable dienophiles in synthetic procedures and the stereochemistry of addition of diphenylcyclopropene to cyclopentadiene has been examined. l,2-Dibromo-3, 

3- difluorocyclopropene yields the dibenzobarrelene (291) and not the expected [4 + 2] adduct [c/.(150)] from reaction with anthracene and it is by no means certain whether the route to (291) involves initial cycloaddition and subsequent rearrange- 

Reagents i, p-NOjC H SOjNj ii, alkaline hydrolysis iii, Ph3P=CH2 iv, CHjIj-Zn/Cu v, Ph3P= l 

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