Bulky peralkylated cyclopentadienes by extension of Jutzi’s pentamethylcyclopentadiene procedure

Phenolat‐Komplexe von Eisen(II) in unterschiedlichen Spinzuständen

“…Die Struktur von 1 b (Abbildung 1) im Kristall zeigt, dass der Abstand des FeAtoms von der Ringebene (1.92 ) viel größer ist als in Octaisopropylferrocen (1.72 [4] ), obwohl letzteres sterisch wesentlich stärker befrachtet ist. Abbildung 2 zeigt die Struktur von 3 a im Kristall.…”

Polymer-Mediated Reactions. A Nazarov-Like Cyclization

“…The reaction of (3E,6E)-2,4,6,8-tetramethylnona-3,6-dien-5-one (19,22 0.194 g, 1 mmol) and 1 (0.57 g, 1 mmol) under the standard condtions gave 3,4-diisopropyl-2,5-dimethylcyclopent-2-enone (21) 24 …”

“…24 There is also the report by West and Geise of a reductive Nazarov cyclization that converted 19 to 20 as a 1.2:2.8:1 mixture of three diastereomers (84% yield), using the BF 3 -silane procedure noted above for the preparation of 10 and 13. 22 When we heated 19 with tosic acid, we obtained a 35% yield of the Nazarov product 21 as a 5:1 trans/cis mixture, but there were several byproducts.…”

“…We chose a series of dienones (3,8,11,14,16,19,22,24,26) for this study that have representative structural features. The chosen dienones allowed us to examine key features of the Nazarov cyclization, including reactivity, regioselectivity, and the diastereoselectivity for those reactions for which it is an issue.…”

Preparation of Substituted Cyclopentadienes through Platinum(II)‐Catalyzed Cyclization of 1,2,4‐Trienes

“…They are useful not only as a reactive diene component in the Diels-Alder reaction [1] but also as a precursor for the preparation of transition-metal complexes with Cp-type ligands.[2] However, the preparation of well-defined, highly substituted cyclopentadienes is not necessarily easy owing to the absence of general methods [3] and also to the facile migration of the endocyclic double bonds.[4] Herein we describe a novel method for the preparation of highly substituted cyclopentadiene derivatives based on the Pt II -catalyzed cyclization of 1,2,4-trienes in which platinumcarbene intermediates play an important role in determining the reaction pathways.We expected that treatment of 1,2,4-trienes with appropriate electrophilic transition-metal complexes [5] would generate a,b-unsaturated carbene complexes III through cyclization of p complex I [6] and/or pentadienyl cationic complex II, and that the produced carbene complex III would further undergo useful transformations to give cyclopentadienes or their derivatives [Eq. (1)].…”