Modifying Positional Selectivity in C-H Functionalization Reactions with Nitrogen-Centered Radicals: Generalizable Approaches to 1,6-Hydrogen-Atom Transfer Processes.

Nitrogen-centered radicals are powerful reaction intermediates owing in part to their ability to guide position-selective C(sp)-H functionalization reactions. Typically, these reactive species dictate the site of functionalization by preferentially engaging in 1,5-hydrogen-atom transfer (1,5-HAT) processes. Broadly relevant approaches to alter the site-selectivity of HAT pathways would be valuable because they could be paired with a variety of tactics to install diverse functional groups.

Sulfamides direct radical-mediated chlorination of aliphatic C-H bonds.

Given the prevalence of aliphatic amines in bioactive small molecules, amine derivatives are opportune as directing groups. Herein, sulfamides serve as amine surrogates to guide intermolecular chlorine-transfer at γ-C(sp) centers. This unusual position-selectivity arises because accessed sulfamidyl radical intermediates engage preferentially in otherwise rare 1,6-hydrogen-atom transfer (HAT) processes through seven-membered transition states.

A five-coordinate iron(III) porphyrin complex including a neutral axial pyridine N-oxide ligand.

While six-coordinate iron(III) porphyrin complexes with pyridine N-oxides as axial ligands have been studied as they exhibit rare spin-crossover behavior, studies of five-coordinate iron(III) porphyrin complexes including neutral axial ligands are rare. A five-coordinate pyridine N-oxide-5,10,15,20-tetraphenylporphyrinate-iron(III) complex, namely (pyridine N-oxide-κO)(5,10,15,20-tetraphenylporphinato-κN,N',N'',N''')iron(III) hexafluoroantimonate(V) dichloromethane disolvate, [Fe(CHN)(CHNO)][SbF]·2CHCl, was isolated and its crystal structure determined in the space group P-1. The porphyrin core is moderately saddled and the Fe-O-N bond angle is 122.

Sulfamate Esters Guide Selective Radical-Mediated Chlorination of Aliphatic C-H Bonds.

Masked alcohols are particularly appealing as directing groups because of the ubiquity of hydroxy groups in organic small molecules. Herein, we disclose a general strategy for aliphatic γ-C(sp )-H functionalization guided by a masked alcohol. Specifically, we determine that sulfamate ester derived nitrogen-centered radicals mediate 1,6-hydrogen-atom transfer (HAT) processes to guide γ-C(sp )-H chlorination.

Synthesis of N-Substituted Sulfamate Esters from Sulfamic Acid Salts by Activation with Triphenylphosphine Ditriflate.

A general approach to access sulfamate esters through preparation of sulfamic acid salts, subsequent activation with triphenylphosphine ditriflate, and nucleophilic trapping is disclosed. The method proceeds in modest to excellent yields to incorporate nucleophiles derived from aliphatic alcohols and phenols. This approach can be employed to furnish differentially substituted sulfamides.