Bulky peralkylated cyclopentadienes by extension of Jutzi’s pentamethylcyclopentadiene procedure

In alkaline solution pentanone-3 undergoes a condensation reaction with isobutyraldehyde to form trans-4,6-dimethylhept-5-en-3-one (1) and 3,5-diisopropyl-2,6-dimethyl-2,3,5,6-tetrahydro-γ-pyrone (2) upon addition of isobutyraldehyde to 1. Treatment of 2 with p-toluenesulfonic acid under mild conditions gives 2,5-dimethyl-3,4-diisopropylcyclopent-2-en-1-one (3) with concomitant loss of water. With methyl- or isopropylmagnesium chloride 3 can be converted to tautomeric mixtures of the respective 1,2,3,4,5-pentaalkylated cyclopentadienes HC5Me2(CHMe2)3 (4) or HC5Me3(CHMe2)2 (5), which on deprotonation with sodium amide yield the sodium salts NaC5Me2-3,5-(CHMe2)3-1,2,4 (6) or NaC5Me3-3,4,5-(CHMe2)2-1,2 (7). From 6 or 7 and MnCl2 or [FeBr2(DME)] the novel metallocenes [{C5Me3(CHMe2)2}2Mn] (8), [{C5Me3(CHMe2)2}2Fe] (9), and [{C5Me2(CHMe2)3}2Fe] (10) have been prepared and investigated by spectroscopic and analytical methods. Complex 8 as well as octaisopropylferrocene (11) could also be characterized by X-ray crystal structure determination.