Enantioenriched organoboron compounds are useful chiral building blocks in synthetic chemistry, because they can be readily applied to the stereospecific functionalization of stereogenic C−B bonds. Considerable research efforts have recently been devoted to the development of new methods for the enantioselective monoboration and diboration reactions of prochiral C=C bonds. Despite significant progress in this area during last two decades, there have not been any reports for the development of C−B bond-forming dearomatization of aromatic compounds. The lack of research in this area would be caused by the high energy barrier in the dearomatization process. The development of an enantioselective C−B bond forming dearomatization reaction would make aromatic compounds rich resources of various chiral organoboron compounds. This will provide an attractive approach for the synthesis of complex, functionalized cyclic compounds in combination with the stereospecific transformation of a stereogenic C−B bond. Herein, we report the first enantioselective borylative dearomatization of indoles using a diboron compound, t-BuOH as a proton source, and copper(I)/(R,R)-3,5-xyl-BDPP complex as the catalyst. This reaction would allow the synthesis of chiral indolines containing consecutive stereogenic centers at their 2 and 3 positions with good yields, high regioselectivities, high diastereoselectivites and enantioselectivities (Scheme 1). The results of this study can provide further opportunities for the development of novel stereoselective dearomative borylation reactions involving a wide variety of aromatic compounds.

Regio-, diastereo-, and enantioselective borylative dearomatization of indoles using copper(I) catalysis

253rd National Meeting (2017)

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