Formation of N-sulfonyl imines from iminoiodinanes by iodine-promoted, N-centered radical sulfonamidation of aldehydes

Abstract

A mild and operationally convenient formation of synthetically valuable N-sulfonyl imines from a range of aryl aldehydes by reaction with iminoiodinanes (PhI[double bond, length as m-dash]NZ) and I has been developed. According to mechanistic experiments described within, the reaction is speculated to proceed through an unconventional light-promoted, N-centered radical (NCR) pathway involving a N,N-diiodosulfonamide reactive species. This method not only provides a new pathway toward the production of activated imines, but also serves as an example of a non-traditional means of carbonyl activation via an NCR species.

Visible-Light, Iodine-Promoted Formation of N-Sulfonyl Imines and N-Alkylsulfonamides from Aldehydes and Hypervalent Iodine Reagents

“…We have previously described the formation of N -sulfonyl aldimines, using iminoiodinane reagents and aryl aldehyde reagents, that is believed to proceed through an N-centered radical (NCR) pathway ( Scheme 2 ) [ 49 ]. During our initial investigation, N , N ′-diiodosulfonamide, formed from iminoiodinane and I 2 , was isolated and shown to be a likely reactive species in the reaction [ 49 ].…”

“…We have previously described the formation of N -sulfonyl aldimines, using iminoiodinane reagents and aryl aldehyde reagents, that is believed to proceed through an N-centered radical (NCR) pathway ( Scheme 2 ) [ 49 ]. During our initial investigation, N , N ′-diiodosulfonamide, formed from iminoiodinane and I 2 , was isolated and shown to be a likely reactive species in the reaction [ 49 ]. N , N ′–Diiodosulfonamide moieties are highly reactive species, in which both of the available N–I bonds can be activated by ambient light without the need for a transition-metal catalyst, UV photoreactor, or external chemical initiator.…”

“…In our initial attempt to form N -sulfonyl aldimine, 4-bromobenzaldehyde ( 1 ) was selected as a representative aldehyde, and tested using PhI(OAc) 2 , I 2 , and a representative sulfonamide (NsNH 2 ) following conditions similar to our previously reported iminoiodinane/I 2 system ( Table 1 , entry 1) [ 49 ]. To our delight, a 34% yield was obtained using 1 equivalent of PhI(OAc) 2 , and was improved to 42% (entry 2) when the amount of PhI(OAc) 2 was increased to 2 equivalents.…”

“…In addition to traditional approaches of aldehyde/sulfonamide condensation, methods involving the non-dehydrative reaction of aldehydes with isocyanate analogues have been reported ( Scheme 1 , method B) [ 44 , 45 , 46 ]. Resulting from our research group’s interest in the utilization of N-centered radical (NCR) precursors for C–N bond formation [ 47 , 48 , 49 ], we have recently reported a mild alternative for imine formation that uses iodine and pre-formed iminoiodinane reagents in the presence of light ( Scheme 1 , method C), which addresses many of the shortcomings of traditional methods [ 49 ]. NCR-mediated reactions have seen substantial advances recently, due to the advent of visible-light photoredox catalysis and the development of predictable NCR precursors [ 50 , 51 , 52 ], but there have been very few reports that have utilized NCR species for carbonyl activation [ 49 , 53 , 54 , 55 ].…”

“…Resulting from our research group’s interest in the utilization of N-centered radical (NCR) precursors for C–N bond formation [ 47 , 48 , 49 ], we have recently reported a mild alternative for imine formation that uses iodine and pre-formed iminoiodinane reagents in the presence of light ( Scheme 1 , method C), which addresses many of the shortcomings of traditional methods [ 49 ]. NCR-mediated reactions have seen substantial advances recently, due to the advent of visible-light photoredox catalysis and the development of predictable NCR precursors [ 50 , 51 , 52 ], but there have been very few reports that have utilized NCR species for carbonyl activation [ 49 , 53 , 54 , 55 ]. In order to develop an even more practical and operationally simple method, we aimed to use commercially available, stable reagents such as sulfonamide and (diacetoxyiodo)benzene (referred to as PhI(OAc) 2 or PIDA) under relatively mild conditions.…”