Nucleophilic additions to carbon-heteroatom bonds

Stabilized carbanions can be easily generated at activated positions. An example is that of the Reissert compound shown in Eq. 13, which imdergoes deprotonation in a dichloromethane-water system in the presence of TEBAC, then condenses with aldehydes.54 The alkylation of the anion is discussed below (p. 138). 

Aromatization occurs by transposition of the benzoyl group from the nitrogen atom to the alcohol functionality. The subsequent hydrolysis of the benzamide group vide infra) can be achieved without isolation of the intermediate, and the one-pot, two-reaction sequence is completed within 90 min. The other examples described below deal with the reactions of enolates and similar compoimds. 

53 Sun, X. Peng, G. Huaxue Tongbao 1990,45-7, 9 Chem Abstr. 1991,114,101104q. 

The synthesis of various tetracyclones was reported using PTC under sonication (Eq. 14).55 Instead of refluxing ethanol, toluene at room temperature is a more appropriate medium. A similar crotonization reaction was effected in the presence of basic alumina on the 1/4 molar scale.56 No PTC is needed. 

Calcined barium hydroxide is an efficient catalyst for a number of base-mediated reactions. Among these, the Claisen-Schmidt condensation of acetophenones with benzaldehydes occurs in times as short as 10 min at room temperature (Eq. 15). The acetophenone enolate (detected by IR spectroscopy) is formed on the catalyst surface, where the reaction with the aldehyde takes place. The higher activity of the ketone enolate is interpreted by the authors as the result of an increased vibrational state of the lattice , a formulation close to the mechano-chemical explanation. With the help of selective poisoning experiments, it is concluded that the enolate forms via a SET mechanism. 

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