Electron-deficient 1-aza-1,3-butadienes containing a 1,2-benzoisothiazole-1,1-dioxide or 1,2,3-benzoxathiazine-2,2-dioxide motif act as regio- and chemoselective dienophiles in normal-electron-demand Diels-Alder reactions with HOMO-raised trienamines, rather than typical 4π-participation in inverse-electron-demand versions. The enantioenriched cycloadducts could be efficiently converted to spiro or fused frameworks with high structural and stereogenic complexity by a sequential aza-benzoin reaction or other transformations.
A useful approach is developed for the synthesis of various structurally interesting spirocyclic sultams and heterobiaryls using a cross-dehydrogenative coupling strategy that features high atom and step economy. This method employs [Cp*RhCl2]2 as a catalyst and N-sulfonylimine, a weak coordinating group, as an efficient directing group to assist C-H activation. A number of the coupled products were converted into interesting molecules through further synthetic transformations.
1-Azadienes as Regio-and Chemoselective Dienophiles in Aminocatalytic Asymmetric Diels-Alder Reaction. -Azadienes (I) and (VI) act as regio-and chemoselective dienophiles in the amine catalyzed asymmetric Diels-Alder reactions with dienal (II). The resulting enantioenriched cycloadducts are cyclized to spiro or fused frameworks. -(MA, C.; GU, J.; TENG, B.; ZHOU, Q.-Q.; LI*, R.; CHEN, Y.-C.; Org. Lett. 15 (2013) 24, 6206-6209, http://dx.doi.org/10.
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