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Cyclovinylogous Additions of 1,3-Diphenylbenzofuran to 1,3,5-Cycloheptatriene
Kaupp, Gerd,Grueter, Heinz-Willi,Teufel, Eberhard
, p. 618 - 629 (2007/10/02)
1,3-Diphenylbenzofuran (1) reacts thermally with 3,4-dimethylenecyclobutene (2) and 1,3,5-cycloheptatriene (5) to give exo- and endo-Diels-Alder adducts.The reaction of 1 with potassium cycloheptatrienide leads to substitutive adducts (13, 14) at low temperature, but to -ring closure (15) at higher temperatures, via the anionic intermediate 12.The photoaddition of 1 to 5 gives the exo- and endo--, endo--, exo--, and cis-1,4(1,3)-substitutive adducts 7, 6, 16, 17, and 14 in divergence to recent literature data.The structures of the products are elucidated by 1H NMR spectra and in part by chemical transformations, their formation can be interpreted in terms of the approved diradical mechanism.The endo-/exo-isomerization of 16 into 19 proceeds solvolytically.The products 7 and 16 are formed out of 17 by suprafacial thermal 1,3-alkyl shifts.Further exo- and endo-- as well as -additions of 1 are achieved with dimethyl maleate (23, 24) and anthracene (26), resp.
