Cycloaddition reactions of diarylalkylidenecycloproparenes

Cycloproparenes

“…In the benzene series, DPIBF is incorporated with addition exclusive to the bridge bond . The norcaradiene-bridged endo -adducts 258 shown in Scheme are confirmed as products from X-ray crystallographic analysis of 258b ; no products attributable to reaction across the exocyclic double bond or the three-membered ring σ bond were detected. , In contrast, the naphthalene homologues 168 react somewhat more readily and both DPIBF and α-pyrone add, but only at the exocyclic double bond. , It is presumed that the spirocyclic intermediates so formed are too unstable to survive the conditions and ring expand with relief of steric strain to give the cyclobutarenone 259 and the indanone 260 , respectively (Scheme ). These observations match expectation as the cyclopropanaphthalene derivatives avoid high-energy orthoquinonoid structures equivalent to 258 that would result from loss of aromaticity in any addition to the bridge …”

“…289,290 In contrast, the naphthalene homologues 168 react somewhat more readily and both DPIBF and R-pyrone add, but only at the exocyclic double bond. 289,291 It is presumed that the spirocyclic intermediates so formed are too unstable to survive the conditions and ring expand with relief of steric strain to give the cyclobutarenone 259 and the indanone 260, respectively (Scheme 61). These observations match expectation as the cyclopropanaphthalene derivatives avoid high-energy orthoquinonoid structures equivalent to 258 that would result from loss of aromaticity in any addition to the bridge.…”

“…Cycloaddition chemistry of the diarylalkylidenecycloproparenes has received attention − and the behavior easily differentiates the benzene 167 and naphthalene 168 series. For none of the compounds are additions easy to bring about but use of ethylene glycol is efficacious.…”

From Solvolysis to Self-Assembly

“…However, after Brian’s return to Wellington, the alternative Peterson olefination of 39 worked well; that started a decade-plus long trans-oceanic collaboration with Brian, which resulted not only in nearly 20 joint publications but also a lifelong friendship. In a collaborative fashion, we investigated the electrochemical properties, photoelectron spectra, polarity, 13 C NMR and ambiphilicity of these novel strained hydrocarbons. We explored their reactions with both electrophiles and nucleophiles .…”