Mehrstufige Redoxsysteme. XLIX. Mitteilung. Mit π-Systemen substituierte 1,3-Dimethylidencyclobutane: Synthese und Eigenschaften

Multistep Redox Systems. 1,3-Dimethylidenecyclobutanes Substituted by π-Syntheses and Properties As potential redox systems 1,3-dimethylidenecyclobutanes are synthesized in which the ‘exo’-methylidene group participates in a cyclopentadienyl (type C4 )or cycloheptatrienyl (type A5 ) system. Benzo-annellated systems are also described. The formation of the C?C bond by the reaction of thioketones ( 3 and 31 ) with diazo compounds is extended to extended to 1,6,7,21 , and 24 , which so far had not been employed. In some cases, intermediate thiiranes can be isolated (e.g. 4 ) which are smoothly transformed into the target compounds of types C4 and A5 by extrusion of sulfur. The new C?C bonds may be introduced stepwise, thereby allowing the synthesis of unsymmetrically substituted 1,3-dimethylidenecyclobutanes (e.g. 20 and 35 ). Reduction of by Na does not produce bicyclobutanes but compounds 43 and 44 with one dihydrofulvene unit.