152874-24-3Relevant academic research and scientific papers
A Novel Route to Isoannulated Heteroaromatic Compounds, 1. - Synthesis and Reactions of Furofurans, Thienofurans, Furobenzofurans, and Benzothienofurans
Eberbach, Wolfgang,Laber, Norbert,Bussenius, Joerg,Fritz, Hans,Rihs, Grety
, p. 975 - 996 (2007/10/02)
A general method for the synthesis of furo- and thienofurans 4 - 7 has been developed.The reaction principle is based on the thermal transformation of suitably structured epoxyhexenynes (15 -19) following the general reaction sequence 1 -> 2 -> 3 (annulation type A).Derivatives of the so far unknown diheteropentalenes furofuran (4b, c, d, g, h), furobenzofuran (6b, d, e, 45) as well as benzothienofuran (7b, d) are obtained by short-time thermolysis.Likewise two representatives of the previously reported thienofuran system are prepared (5b, c).By flash vacuum thermolysis the benzo-annulated epoxyhexenyne 19b rearranges in poor yield to the isobenzofuran 52 (identified as dimethyl acetylenedicarboxylate adduct 47) and 2-cyano-α-naphthol (46).The structure of the furofuran 4b has been established by X-ray structural analysis.A mechanistic explanation of the transformation of the epoxyhexenynes to diheteropentalenes is proposed.Indications for the occurrence of carbenes as product-determining species are obtained with the phenylcyano-substituted oxiranes 15c, h and 17e which - in addition to the furofurans 4c, h and 6e - lead to the furylindenes 31c, h/32c, h and 41, resp..The Diels-Alder reactivity of the furo- and thienofurans 4g, 5b, c, and 6b has been examined.Key Words: Pentalenes, dihetero- / Cyclizations, 1,7-dipolar / Carbonyl ylides / Cycloallenes / Diels-Alder reactions / o-Quinodimethanes, hetero analogues
