Aerobic Aromatization–Driven C–C Bond Cleavage as a Route to Reduced-Carbon Alcohols

Alcohols turn up so frequently in synthesis that it’s easy to forget how varied their roles really are—sometimes they’re functional handles, other times they’re structural placeholders, and in many drug molecules they’re essential for binding or solubility. Because of that, chemists have accumulated a long list of reliable ways to make them. Most of us learn early on to reach for substitutions of activated precursors, or the familiar hydration and hydroboration–oxidation sequence for alkenes, or, when needed, one of the many carbonyl-reduction protocols. These reactions usually behave well, but they share a rather fundamental limitation: they don’t disturb the carbon framework. When the goal is to trim a carbon unit from a ketone or reshape a backbone, the typical methods don’t offer much help. For more than a century, the Baeyer–Villiger oxidation has served as the workaround. The idea—slipping an oxygen atom next to the carbonyl to generate a lactone, then hydrolysis it to reach an alcohol—is elegant on paper. In practice, though, anyone who has used it knows the drawbacks. Strong peracids introduce safety concerns and increase economic costs. The hydrolysis step requires strong acids or bases, which limits what functional groups survive the sequence. And the migration selectivity, especially with mixed alkyl groups, can be unpredictable enough to require several trial runs. All of this makes the reaction useful but somewhat inflexible, particularly when working with late-stage intermediates or densely functionalized scaffolds.

Over the past several years, a different idea has gained traction: using aromatization as the thermodynamic “pull” needed to cleave stubborn C–C bonds. Pre-aromatized intermediates—such as dihydrobenzothiazolines, dihydroquinazolinones, or dihydrotriazoles—can undergo aromatization-driven β-scission to open C–C σ-bonds that would otherwise remain untouched. This strategy has enabled an interesting mix of transformations, from ketones to various alkyl functionalizations. Still, most examples lean on transition metals, specialized oxidants, or photochemical setups, and very few provide a straightforward route to alcohols from unstrained ketones. The field is still missing a method that is simple to run, broadly tolerant, and genuinely green—one that could handle deacylation without the usual complications.

To this end, new research paper published in Green Chemistry and led by Dr. Renzhi Liu and Professor Huiying Zeng from the Lanzhou University, the researchers created an aerobic, metal-free strategy that converts unstrained ketones into primary, secondary, and even tertiary alcohols through aromatization- driven C–C bond cleavage. Their platform relies on MBHA-derived pre-aromatized intermediates that undergo β-scission to release alkyl radicals, which are then trapped directly by molecular oxygen. The same mechanistic framework enables additional transformations such as spiro-lactam formation, lactonization, and exocyclic olefin synthesis. In essence, they provide a unified oxygen-driven radical editing system that simplifies carbon-skeleton modification in complex molecules.

The team began with a simple test case: dihydro-1,2,4-triazole (1a), Derived from a methyl ketone and heated under a modest oxygen atmosphere and by optimizing temperatures in methanol, they noticed a modest rise in the formation of a peroxide intermediate (2a), an early clue that alkyl radicals were being intercepted directly by oxygen. Switching to ethanol provided a turning point. Upon adding a small volume of water, the alcohol yield climbed even further. Increasing the solvent volume to 0.5 mL produced a consistent 82% yield of 3a, accompanied by the aromatized by-product 4, a hallmark of the PAI activation pathway. According to the authors, these optimizations suggested that the oxygen trapping event and the subsequent reduction of the peroxide intermediate were tightly linked. Moreover, the team found that linear methyl ketones of varying chain lengths delivered the expected alcohols in high yields, and aromatic rings carrying either electron-rich or electron-poor substituents were handled with comparable ease. Even free phenols, esters, amides, ethers, and heteroarenes survived with minimal interference. Estrone, nabumetone, ciprofloxacin, theophylline, and vitamin E derivatives all underwent smooth deacetylation which imply that the method can be carried out stably even in molecules laden with competing functional groups. Furthermore, the authors found that cyclic ketones opened to give triazole-tethered primary alcohols, which suggest that ring strain was not required for scission. A tertiary alcohol could even be assembled through radical addition to an olefin, marking a conceptual expansion beyond simple ketone cleavage. The formation of spiro-lactam analogues and lactones under the same oxidative environment further emphasized how flexible the radical cascade could become once the initial β-scission was triggered. The researchers also ran several control experiments and observed benzoyl-protected analogue stalled completely, pinpointing the N–H bond as essential for radical initiation. TEMPO shut down the reaction and cleanly trapped several intermediates, including nitrogen-centered and carbon-centered radicals. Isotopic labeling with H₂¹⁸O delivered no labeled alcohol, unambiguously proving that the oxygen incorporated into products came solely from O₂.

In conclusion, Dr. Renzhi Liu and Professor Huiying Zeng developed a new method that dispenses with metal catalysts entirely and relies on molecular oxygen as both oxidant and chemical partner. This innovative shift away from peracids and transition-metal oxidants is more than a symbolic gesture: it lowers hazards, reduces cost, and simplifies reaction design to the point that the chemistry becomes almost self-regulating. The transformation proceeds at moderate temperature, tolerates water, and never demands the sort of narrow redox windows that complicate classical Baeyer–Villiger protocols. Additionally, and on a mechanistic level, the study by Dr. Renzhi Liu and Professor Huiying Zeng reveals how aromatization can serve as a structural “anchor” that redirects the flow of radical reactivity. Many radical C–C cleavage reactions suffer from competing pathways, often producing ill-defined mixtures or requiring tailored catalysts to impose order. In contrast, the MBHA-mediated pre-aromatized intermediate used here exerts a thermodynamic pull that favors a excellent selectivity for β-scission event. Once the alkyl radical is generated, the presence of O₂ ensures that it is promptly trapped, channeling the system into a predictable peroxide intermediate. The subsequent reduction step, either by substrate or by thiosulfate, completes a cycle that is surprisingly efficient for a mechanistically open-shell process.

We believe the implications for molecular design are important because ketones appear widely in pharmaceuticals and natural products, a reliable method for removing an acyl unit late in a synthetic sequence could open a new category of scaffold modifications. The authors demonstrated this possibility by converting complex bioactive molecules into streamlined alcohol analogues without damaging sensitive motifs such as quinazolines, indoles, lactams, or polycyclic frameworks. Medicinal chemists frequently rely on variations in chain length or polarity to tune biological activity; the ability to contract a carbon skeleton in a single step offers a practical shortcut when classical deoxygenation or demethylation routes prove uncooperative. Beyond alcohol formation, the auxiliary reactions uncovered—radical addition to form tertiary alcohols, spiro-lactam assembly, lactone formation, and exocyclic olefin synthesis—suggest that the platform could evolve into a versatile toolbox for radical editing. This is particularly appealing for settings where metal contamination is unacceptable or where reaction simplicity outweighs maximal efficiency. The study hints at future opportunities, especially the authors’ stated intention to generalize aerobic aromatization-driven C–C activation to a wider array of pre-aromatized intermediates. If such strategies mature, they may gradually shift how chemists think about oxidative skeletal editing, moving from specialized catalyst designs toward oxygen-driven self-propagating systems.