Development of new hypervalent iodine reagents with improved properties and reactivity by redirecting secondary bonds at iodine center

摘要

Hypervalent iodine reagents have found wide application in organic synthesis as versatile, efficient, and environmentally sustainable reagents. Particularly important hypervalent iodine reagents used as atom and group transfer reagents include: iodosylbenzene, (PhIO)_n, (tosylimino)iodobenzene, (PhINTs)_n, and iodonium ylide, PhI = C(CO_2CH_3)_2. Despite the significant interest in these reagents as primary sources of "O", "NR" and "CR_2" units in transition metal catalyzed processes, their practical application is hampered. In particular, their tightly aggregated and polymeric structures in the solid state render these polyvalent iodine species insoluble in all nonreactive media and prevent their use in chemical reactions under homogenous conditions, which can be undesirable for many synthetic and mechanistic studies. In this review we describe our work on the rational design and development of new soluble, thermally stable, and highly reactive hypervalent iodine reagents based on structural modifications that lead to redirection of secondary bonding from intermolecular to intramolecular modes. Specifically, the introduction of a coordinating donor in the ortho-position of the phenyliodine (Ⅲ) moiety leads to a significant improvement of solubility of a hypervalent iodine reagent. Based on this approach, we have developed a series of new hypervalent iodine reagents, which can be used as selective oxidants, nitrene or carbene precursors, and atom transfer reagents. Specific examples of these new reagents are represented by iodosylarenes and iminophenyliodanes bearing tert-butylsulfonyl group in the ortho-position of the phenyl ring and by the ortho-alkoxy substituted iodonium imides and ylides. These new pseudocyclic (and cyclic) reagents have excellent solubility in organic solvents and can be used as efficient reagents for catalytic formation of new C-O, C-N and C-C bonds, as well as to enable the generation and detection of highly reactive metal species involved in catalysis and biomimetic reactions.