期刊
ACS CATALYSIS
卷 7, 期 6, 页码 4189-4196出版社
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.7b00975
关键词
hypervalent iodine; asymmetric catalysis; transition state; helical chirality; reaction mechanism; stereoselectivity
The need for metal-free environmentally benign catalysts has provided a strong impetus toward the emergence of hypercoordinate iodine reagents. At this stage of development, molecular insights on the mechanism and origin of stereo selectivity are quite timely. In this study, the origin of stereoinduction in a class of iodoresorcinol-based chiral hypercoordinate iodine-catalyzed synthesis of biologically important spirocyclic bisoxindoles from aryl dianilides has been established by using density functional computations. Formation of an interesting helical fold by the 2,6-chiral amide arms on the resorcinol framework is found to be facilitated by a network of noncovalent interactions. In the chiral environment provided by the helical fold, enantioselectivity is surprisingly controlled in a mechanistic event prior to the ring closure to the final spirocyclic product, unlike that commonly found in spirocyclic ring formation. A vital 1,3-migration of the chiral aryl iodonium (Ar*-I(CF3COO)) in an O-iodonium enolate to the corresponding C-iodonium enolate, which retains the chiral memory, holds the key to the enantiocontrol in this reaction and thus renders ring closure to be stereospecific.
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