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An advanced undergraduate organic chemistry laboratory experiment involving a rhodium-catalyzed intermolecular hydrocarbon C-H oxidation reaction is described. In the initial phase of this lab, students conduct a C-H amination reaction of ethylbenzene and isolate a benzylic amine product. In the second part of the lab, competition experiments are performed to compare the relative rates of C-H insertion with electronically disparate para-substituted ethylbenzene derivatives. Reaction progress is monitored by thin-layer chromatography and the outcome quantitatively assessed using [superscript 1]H NMR spectroscopy. Data from competition experiments form the basis for a discussion of reaction mechanism including analysis of putative transition structures and relative potential energy barriers for C-H oxidation. Experiments have been designed such that instructors can tailor the level of detail and discussion from introductory to advanced.

Predicting site selectivity in C-H bond oxidation reactions involving heteroatom transfer is challenged by the small energetic differences between disparate bond types and the subtle interplay of steric and electronic effects that influence reactivity. Herein, the factors governing selective Rh2(esp)2-catalyzed C-H amination of isoamylbenzene derivatives are investigated, where modification to both the nitrogen source, a sulfamate ester, and substrate are shown to impact isomeric product ratios. Linear regression mathematical modeling is used to define a relationship that equates both IR stretching parameters and Hammett σ(+) values to the differential free energy of benzylic versus tertiary C-H amination. This model has informed the development of a novel sulfamate ester, which affords the highest benzylic-to-tertiary site selectivity (9.5:1) observed for this system.

Nitrogen-centered radicals are powerful reaction intermediates owing in part to their ability to guide position-selective C(sp3)–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. Yet, until recently, there have been no generalizable strategies to modify the position-selectivity observed in these HAT processes. This Synpacts article reviews transformations in which nitrogen-centered radicals preferentially react through 1,6-HAT pathways. Specific attention will be focused on strategies that employ alcohol- and amine-anchored sulfamate esters and sulfamides as templates to achieve otherwise rare γ-selective functionalization reactions. 1 Introduction 2 Transformations that Rely on Structural Constraints or Weakened C–H Bonds to Favor 1,6-HAT Processes 3 Sulfamate Esters Engage Selective 1,6-HAT Processes 4 Expansion to 1,6-HAT Processes with Masked Amine Substrates 5 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

The synthesis of hennoxazole A, an antiviral marine product from 4-methyloxazole-2-carboxylic acid is described. The direct use of dimethyl acetal for installation of [C.sub.8]-methyl ether in one step and the alkylation of the intact bisoxazole core increases the efficiency of this synthesis.

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(sp3)−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(sp3)−H chlorination. This reaction proceeds through a light-initiated radical chain-propagation process and is capable of installing chlorine atoms at primary, secondary, and tertiary centers. [ABSTRACT FROM AUTHOR]

For more than 70 years, nitrogen-centered radicals have been recognized as potent synthetic intermediates. This review is a survey designed for use by chemists engaged in target-oriented synthesis. This review summarizes the recent paradigm shift in access to and application of N -centered radicals enabled by visible-light photocatalysis. This shift broadens and streamlines approaches to many small molecules because visible-light photocatalysis conditions are mild. Explicit attention is paid to innovative advances in N-X bonds as radical precursors, where X = Cl, N, S, O, and H. For clarity, key mechanistic data is noted, where available. Synthetic applications and limitations are summarized to illuminate the tremendous utility of photocatalytically generated nitrogen-centered radicals.

Photomediated Giese reactions are at the forefront of radical chemistry, much like the classical tin-mediated Giese reactions were nearly forty years ago. With the global recognition of organometallic photocatalysts for the mild and tunable generation of carbon-centered radicals, chemists have developed a torrent of strategies to form previously inaccessible radical intermediates that are capable of engaging in intermolecular conjugate addition reactions. This Review summarizes advances in photoredox-mediated Giese reactions since 2013, with a focus on the breadth of methods that provide access to crucial carbon-centered radical intermediates that can engage in radical conjugate addition processes., (© 2021 Wiley-VCH GmbH.)

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 3 ) 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. The site-selectivity of C-H abstraction can be modulated by adjusting the steric and electronic properties of the sulfamide nitrogen substituents, an ability that has not been demonstrated with other substrate classes. The disclosed reaction relies on a light-initiated radical chain-propagation mechanism to oxidize C(sp 3 )-H bonds efficiently., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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 3 )-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 3 )-H chlorination. This reaction proceeds through a light-initiated radical chain-propagation process and is capable of installing chlorine atoms at primary, secondary, and tertiary centers., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)