Molecular structures of the most prominent chiral non‐racemic hypervalent iodine(III) reagents to date have been elucidated for the first time. The formation of a chirally induced supramolecular scaffold based on a selective hydrogen‐bonding arrangement provides an explanation for the consistently high asymmetric induction with these reagents. As an exploratory example, their scope as chiral catalysts was extended to the enantioselective dioxygenation of alkenes. A series of terminal styrenes are converted into the corresponding vicinal diacetoxylation products under mild conditions and provide the proof of principle for a truly intermolecular asymmetric alkene oxidation under iodine(I/III) catalysis.
Hypervalent iodine(III) reagents have been known for over a century, and their reaction profile is still actively investigated. Recent years have seen impressive improvements in the area of alkene difunctionalization reactions, where new methodologies have become available. Especially chiral non-racemic hypervalent iodine(III) reagents and catalysts have emerged as versatile tools for the realization of important enantioselective transformations.
The catalytic asymmetric Fujiwara-Moritani ring closures of several indole-and pyrrole-based cyclization precursors are reported. These unprecedented oxidative palladium(II)-catalyzed annulations allow for the formation of a stereogenic quaternary carbon atom, and decent levels of enantiocontrol are seen in 5-exo-trig cyclizations (54 % ee for an indole and 76 % ee for a pyrrole) while 6-exo-trig ring closures afford
2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) was employed as chiral ligand in the enantioselective intermolecular Mizoroki-Heck reaction, whereas the use of cognate BINAP(O) (monooxidized BINAP) is unprecedented. The regio- and enantioselectivity of the arylation of representative cyclic alkenes changes dramatically in the presence of hemilabile BINAP(O) instead of BINAP. The arylation of 2,3-dihydrofuran is perfectly regiodivergent (98:2 versus 0:100) and the arylation of cyclopentene is only enantioselective with BINAP(O) [60 versus 10% enantiomeric excess (ee)]. Use of [Pd(2)(dba)(3)]⋅dba (dba=dibenzylideneacetone) instead of Pd(OAc)(2) produces as high as 86% ee in the arylation of cyclopentene.
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