Acenaphthylene with cyclopentadiene

Ferree, W.L, Jr., and Plummer, B.F., Photochemical heavy-atom effect. IV. External and internal heavy-atom effects upon the reaction of acenaphthylene with cyclopentadiene, /. Am. Chem. Soc., 95, 6709,1973. 

It has been reported that 1 //-bcnz / indene (1), l//-benz[e]indene (2), l//-benz[/g] acenaphthylene (3), and 1 //-cyclopenta[/]-phcnanthrene (4), possessing planar carbon frameworks with a single secondary C(.sy 3)H2 centre, exhibit modest acidity in the gas-phase and in DMSO.1 The origin of their amplified acidity compared with cyclopentane, cyclopentene, and cyclopentadiene is the more pronounced anionic resonance, which distributes the negative charge over the whole planar carbon skeleton via mobile n-electrons. 

Similar reactions have been reported for acenaphthylenes, cyclopentenes, p-benzoquinone, nor-bornadiene, cyclopentadiene, 1,3-cyclohexadiene, and 1,5-cyclooctadiene <78CB3037>. The reaction of dimethyl-7-oxabicyclo[2.2. l]hepta-2,5-diene-2,3-dicarboxylate (120) with the 1,3-dithiolone (113) proceeds with the formation of the cycloadduct (121) (Scheme 28) pyrolysis or photolysis of this adduct (121) resulted in a double fragmentation to give the thiophene (122) and the furan (123) <75CC840>. 

---