Cyclopenta pyrrolidines synthesis

Stable at room temperature for a short while. Detailed NMR experiments have demonstrated the non-aromatic property of this brr-electron system [8]. In contrast to the isomeric benzene, fulvene 1 has localized double bonds [9]. Therefore, it behaves like a diene or like a dienophile, and it readily oligomerizes at temperatures above 0°C [7]. In contrast, terminally disubstituted fulvene derivatives such as dimethylfulvene 11 which had been obtained as early as 1906 by Thiele et al. from cyclopentadiene and acetone in methanol in the presence of potassium hydroxide [10], are perfectly stable compounds. A rather efficient new synthesis of 11 and the monosubstituted fulvene derivative 12 by the reaction of cyclopentadiene with unsaturated carbonyl compounds in the presence of pyrrolidine (Scheme 2), has been described by Griesbeck [11]. Dimethylfulvene 11 in this transformation arises via Michael addition of the cyclopenta-dienide ion to the a,j9-unsaturated ketone mesityloxide and a subsequent retro-... 

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