Abstract
The reactivity of benzyl hypervalent iodine intermediates was explored in congruence with the reductive iodonio-Claisen rearrangement (RICR) to show that there may be an underlying mechanism which expands the reasoning behind the previously known C–C bond-forming reaction. By rationalizing the hypervalent iodine’s metal-like properties it was concluded that a transmetallation mechanism could be occurring with metalloid groups such as silicon and boron. Hypervalent iodine reagents such as Zefirov’s reagent, cyclic iodonium reagents, iodosobenzene/BF3, and PhI(OAc)2/BF3 or triflate-based activators were tested. A desirable facet of the reported reaction is that iodine(I) is incorporated into the product thus providing greater atom economy and a valuable functional group handle for further transformations. The altering of the RICR’s ortho-selectivity to form para-selective products with benzyl hypervalent iodine intermediates suggests a mechanism that involves hypervalent iodine-guided electrophilic substitution (HIGES).
Highlights
Hypervalent iodine compounds have been known for over a hundred years, but it was not until their renaissance in the 1990’s that many of these useful reagents became a staple in synthetic chemistry laboratories [1,2]
Hypervalent iodine reagents are commonly used in oxidation reactions, they have found their own niche in useful C–C bond-formation and C–H activation reactions [3,4,5]
In the reaction with PhI(OAc)2 (1a), 0.5 equiv triflic anhydride, and BnM, a 72% yield of a coupled product was isolated, but the connection was unexpectedly at the para- not the ortho-position as the reductive iodonio-Claisen rearrangement (RICR) might have predicted (Table 1). Further experiments of this hypervalent iodine-guided electrophilic substitution (HIGES) reaction were performed by varying the hypervalent iodine starting material, the activator, the solvent, and the temperature at which the activated hypervalent iodine reagent formed (Table 1)
Summary
Hypervalent iodine compounds have been known for over a hundred years, but it was not until their renaissance in the 1990’s that many of these useful reagents became a staple in synthetic chemistry laboratories [1,2]. Exceptional progress has been made in investigating the RICR’s substrate scope (electron-donating versus electron-withdrawing substituents on PhI(OAc)2 (1a)), mechanism (deuterium labelling studies), product yields and selectivities based on appropriate solvents, temperatures, and Lewis acids [9,10,11]. Further experiments of this hypervalent iodine-guided electrophilic substitution (HIGES) reaction were performed by varying the hypervalent iodine starting material, the activator, the solvent, and the temperature at which the activated hypervalent iodine reagent formed (Table 1).
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