The Aza Diels-Alder Reaction Of α-Ethynyl Ketene-S,S-acetals And Arylimines In The Synthesis Of 4-Functionalized Quinolines

α-Oxo ketenedithioacetals are applied extensively in organic synthesis as a kind of versatile intermediates and are widely studied since the space electron effects of alkylthio groups.During the course of our studies on the chemistry ofα-Oxo ketene-S, S-acetals,α-ethynyl ketene-S, S-acetals as versatile intermediates in organic synthesis has been recognized. The electron-rich terminal alkynyl of it has both the nucleophilic center and electrophilic center. The activity which absorbs more attention and attempt makesα-ethynyl ketene-S, S-acetals have a wide application in synthysis. One of them is the aza Diels-Alder reaction ofα-ethynyl ketene-S,S-acetals and arylimines in the synthesis of 4-functionalized quinolines(The structure of 8a was confirmed by X-ray crystal analysis Scheme a).To get insight into the reaction ,various arylamines and aldehydes was investigated and the main results are listed as follows.α-Ethynyl ketene-S,S-acetals (Scheme b') form fromα-acetyl ketene dithioacetals (Scheme b). It can react in a one pot procedure with various arylamines and aldehydes give the corresponding quinoline derivatives via a consecutive arylimine formation, regiospecific aza-Diels-Alder (Povarov) reaction, and reductive amination in dichloromethane within five minutes. This reaction had following advantages: (1) the readily available starting materials and cheap reagents; (2) a procedure proceeded fast under mild conditions. (3) It occurs at the carbon-carbon triple bond in a highl regioselective manner. Therefore, the reaction not only expanded the synthetic applications of Diels-Alder reaction but also provided a facile and efficient synthetic procedure for the synthesis of 4-functionalized quinoline derivatives.In this paper, 21 new products were synthesized and characterized by IR, ~1H NMR, MS.