UNSATURATED SYSTEMS, ISOMERIZATIONS, POTASSIUM

Introduction. Solutions of f-BuOK in DMSO are highly basic because the solvent strongly complexes with potassium cations, producing activated ligand-separated and dissociated f-butoxide anions in a medium of high dielectric constant. This base/ solvent system is capable of deprotonating weakly acidic carbon and other acids.It is widely used to effect /3-elimination reactions and isomerizations of unsaturated systems. DMSO K+ is present in low concentrations in f-BuOK/DMSO solutions. ... 

Imines derived from benzylamine and a,3-unsaturated ketones which represent 1-azadiene systems can be isomerized to the corresponding 2-azadienes with potassium t-butoxide. Addition of r-butyl-lithium occurs smoothly to afford simple imine anions that undergo alkylation in the usual fashion. 3S The two examples provided in Scheme 17 illustrate the power of this method to provide either a,a- or a,a -substitution. On the other hand, reaction of similar 1-azadiene systems with Grignard reagents results in addition to form the imine anion directly (equation 44). This example represents one of the early contributions to asymmetric induction in this area and will be elaborated in Section 4.1.3.5. 

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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