1,3-bis(diarylmethylidene)-2-methylidenecyclohexanes in cycloaddition and cyclodimerization reactions. The role of stereoelectronic factors.
Cycloaddition and cyclodimerization reactions of 1,3-dibenzylidene- and 1,3-bis(p-methoxybenzylidene)-2-methylidenecyclohexanes, i.e., the diaryltrienes with fixed S-cis-configurations of exocyclic double bonds are studied. These compounds undergo in situ cyclodimerization of the [4 + 2]-type upon dehydration of the precursor tertiary alcohols and form endo-adducts in the Diels-Alder reaction with N-phenylmaleimide. In the presence of CF3COOH, acid-catalyzed cyclodimerization takes place leading to methylidene-substituted spirocyclodimers, which undergo intramolecular cyclization upon prolonged contact with CF3COOH to form a fused carbocyclic system containing a central, 'three-petal' fragment of six-membered rings.
Cycloadditions of allyl cations, 25. Acid catalyzed dehydrative cyclodimerization of 2,4‐dimethyl‐3‐penten‐2‐ol in two phases. Biomimetic one‐pot preparation of 3,3,5,5‐tetramethyllimonene (4‐isopropenyl‐1,3,3,5,5‐pentamethyl‐1‐cyclohexene)
Cycloadditionen von Allyl-Kationen, 25. Saurekatalysierte dehydrative Cyclodimerisierung von 2,4-Dimethyl-3-penten-2-ol in zwei Phasen. Biomimetische Eintopfdarstellung von 3,3,5,5-Tetramethyllimonen (4-Isopropenyl-1,3,3,5,5-pentamethyl-1-cyclohexen) 
 
 
 
2,4-Dimethyl-3-penten-2-ol (1) wurde in einer Mischung von wasriger Sulfonsaure/Pentan bei Raumtemperatur geruhrt. Es bildete sich 3,3,5,5-Tetramethyllimonen (2) in hoher Ausbeute. 2 wurde in sein Epoxid (3) (4-Isopropenyl-1,3,3,5,5-pentamethyl-7-oxabicyclo[4.1.0]heptan) umgewandelt.
Fragmentation reactions of 1,3,5-triferrocenyl-4-(1-ferrocenylvinyl)-, 1-aryl-4-(1-arylvinyl)-3,5-diferrocenyl-, and 3,5-diaryl-1-ferrocenyl-4-(1-ferrocenylvinyl)cyclohexenes
Abstract Monocyclic ferrocenylsubstituted terpenoids, produced upon proton-induced cyclodimerization of ferrocenyl-1,3-dienes, undergo fragmentation under the action of electrophilic agents (HBF 4 , [PhCHFc]BF 4 , or [MeOC 6 H 4 CHCHCHC 6 H 4 OMe]BF 4 ) to give two molecules of methyl-, (2-ferrocenyl-2-phenylethyl)-, or 2,4-bis(p-methoxyphenyl)-3-butenyl-ferrocenylallylium tetrafluoroborates. Treatment of these salts with dimethylaniline yields, depending on their structure, the starting cyclodimers, seven-membered cyclic compounds, dimethylaniline alkylation products, or tricyclic compounds.