81357-84-8Relevant academic research and scientific papers
Butadienyloxirane-Dihydrooxepine Isomerisation. Ring Expansion Reactions of Sterically Fixed and Benzoannelated Epoxyhexadienes by 1,7-Electrocyclisation of Conjugated Carbonyl Ylides
Eberbach, Wolfgang,Trostmann, Uwe
, p. 4035 - 4058 (2007/10/02)
Thermal ring cleavage of specifically substituted oxiranes results in the formation of conjugated carbonyl ylide intermediates which react by 1,5- and/or 1,7-electrocyclisation to give ring expanded products.While the spirooxiranes 5t, 6t, and 12t are transformed, as expected, only into 2,3-dihydrofuranes (21, 22, 50), the geometrically fixed compounds give rise to the formation of seven-membered ring isomers either partially (6c), or predominantly (5c), or exclusively (7-11, 12c). 1,7-Dipolar cyclisations also take place with participation of one or even two aromatic double bonds (7 -> 52, 8 -> 53, 9 -> 54, 12c -> 57, and 10 -> 55, 11 -> 56, resp.) affording mono- and dibenzo-dihydooxepines, respectively.The rearrangements of 5c to 27 and 6c to 28 show for the first time that the 8?-ring closure of 2-oxaheptatrienyl dipoles proceeds in the theoretically predicted conrotatory manner.The exclusive, i. e. periselective formation of dihydrooxepines during the thermolysis of compounds 7 - 11, 12c is explained by assuming a helical geometry of the dipolar intermediates in which the stereoelectronic situation is specially suitable for the - entropically less advantageous - 1,7-cyclisation process.
ZUR STEREOCHEMIE DER 1,7-DIPOLAREN CYCLISIERUNG VON KONJUGIERTEN CARBONYL-YLIDEN
Eberbach, Wolfgang,Haedicke, Erich,Trostmann, Uwe
, p. 4953 - 4956 (2007/10/02)
The 8e-cyclization of the conjugated carbonyl ylide 15, generated by thermolysis of butadienyloxirane 9, takes place in the theoretically expected conrotatory fashion yielding the cis-2,3-dihydrooxepin 11.The stereochemical assignment has been established by X-ray analysis of the Diels-Alder adduct 12.
