Stepwise Suzuki−Miyaura Cross‐Coupling of Triborylalkenes Derived from Alkynyl−B(dan)s: Regioselective and Flexible Synthesis of Tetrasubstituted Alkenes

Alkenes with three boryl groups of differing reactivities were synthesized and subsequently cross‐coupled regioselectively with aryl halides in a stepwise manner to afford tetrasubstituted alkenes. The key triborylalkene is derived from the platinum‐catalyzed diboration of alkynyl−B(dan)s with B 2 (pin) 2 . Due to excellent regioselectivity and reaction efficiency of each step starting with alkynyl−B(dan)s, tetrasubstituted alkenes with desired carbon frameworks at desired positions can be prepared in high yields. For example, an alkene with four distinct aryl groups, p ‐MeOC 6 H 4 , p ‐CF 3 C 6 H 4 , p ‐MeC 6 H 4 , and p ‐NCC 6 H 4 , was obtained in 71% overall yield via six steps, starting with the dehydrogenative borylation of p ‐MeC 6 H 4 C≡CH with HB(dan). Moreover, a variety of tetrasubstituted alkenes, including regio‐ and stereoisomers of the above tetraarylalkene, AIE‐active TPTPE and derivatives thereof, and ( Z )‐tamoxifen, a well‐known breast cancer drug, were accessed via the developed strategy.