A New Method Of Research Gold Catalytic Direct Aldol Reaction

As one of the most practical ways to build up carbon-carbon bonds between organic molecules, the aldol reaction commonly involves two carbonyl compounds as the nucleophile and electrophile, respectively. One popular method is performing the enolization of the particular carbonyl compound in advance of the transformation. As another important strategy, the direct aldol reaction, featured with the selective formation of enolates or equivalents in the presence of the electrophile, has appeared in recent decades. To date, this field mostly focuses on direct aldol reactions of two carbonyl compounds, especially their catalyzed versions using catalysts. In recent years, the direct aldol reaction involving masked carbonyl compounds has appeared as another important alternative. As a result, carbonyl compounds are no longer the exclusive starting materials. Herein, we present a new approach to the direct aldol reaction as the first example involving not only the in-situ formation of the enol ether but also the simultaneous activation of the electrophile through a gold-catalyzed intermolecular methoxy group transfer. Two masked carbonyl compounds, dimethyl acetals and terminal alkynes, were employed as the starting materials. It is noteworthy that this transformation possesses two features:(i) this process can only work with acetals rather than aldehydes since alkynes and dimethyl acetals are both activated at the same time,(ii) an interesting ligand effect had been observed. As terminal alkynes involved, an electrophilic gold complex had been formed as the Buchwald-type ligand featuring the gold complex,(t-Bu)2(o-biphenyl)PAuCl/AgNTf2, we applied, however, a nucleophilic gold complex that had been mainly generated when was employed.