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1. Photochemical Uncaging of Aldehydes and Ketones via Photocyclization/Fragmentation Cascades of Enyne Alcohols: An Unusual Application for a Cycloaromatization Process

   https://doi.org/10.3390/molecules28155704  

   Campbell, Adam; Dos Santos, Nikolas R.; Alabugin, Igor (August 2023, Molecules)

   We utilized a cycloaromatization reaction driven by relief of excited state antiaromaticity to photouncage aldehydes and ketones. We developed several synthetic routes towards the synthesis of photocaged carbonyls as allylically substituted 3-(2-(arylethynyl)phenyl)prop-2-en-1-ols. A library of photocaged aryl aldehydes and ketones containing donors and acceptors, as well as several photocaged fragrance aldehydes and the steroid 5α-cholestan- 3 -one, were synthesized and demonstrated photouncaging in good to excellent yields. 

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2. Zirconium-catalyzed asymmetric Kabachnik–Fields reactions of aromatic and aliphatic aldehydes

   https://doi.org/10.1039/d1sc03222d  

   Dai, Yijing; Zheng, Li; Chakraborty, Debarshi; Borhan, Babak; Wulff, William D. (September 2021, Chemical Science)

   null (Ed.)

   An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik–Fields reaction to give α-aminophosphonates. A catalyst was sought that would give high asymmetric inductions for aromatic and, and more particularly, for aliphatic aldehydes since there has not previously been an effective catalyst developed for this class of aldehydes. The optimal catalyst is prepared from three equivalents of the 7,7′-di- t -butylVANOL ligand, one equivalent of N -methylimidazole and one equivalent of zirconium tetraisopropoxide. This catalyst was most efficient in the presence of 10 mol% benzoic acid. Optimal conditions for aryl aldehydes required the use of 3,5-diisopropyl-2-hydroxyaniline and gave the aryl α-aminophosphonates in up to 96% yield and 98% ee over 11 different aryl aldehydes. The best aniline for aliphatic aldehydes was found to be 3- t -butyl-2-hydroxyaniline and gave the corresponding phosphonates in up to 83% yield and 97% ee over 18 examples. The asymmetric inductions for aliphatic aldehydes were comparable with those for aromatic aldehydes with a mean induction of 90% ee for the former and 91% ee for the latter. The best method for the liberation of the free amine from the aniline substituted α-aminophosphonates involved oxidation with N -iodosuccinimide. 

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3. Cobalt‐Catalyzed Aerobic Oxidative Cleavage of Alkyl Aldehydes: Synthesis of Ketones, Esters, Amides, and α‐Ketoamides

   https://doi.org/10.1002/chem.202101035  

   Li, Tingting; Hammond, Gerald_B; Xu, Bo (May 2021, Chemistry – A European Journal)

   Abstract A widely applicable approach was developed to synthesize ketones, esters, amides via the oxidative C−C bond cleavage of readily available alkyl aldehydes. Green and abundant molecular oxygen (O₂) was used as the oxidant, and base metals (cobalt and copper) were used as the catalysts. This strategy can be extended to the one‐pot synthesis of ketones from primary alcohols and α‐ketoamides from aldehydes. 

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4. Ir( iii )-catalyzed ortho C–H alkylations of (hetero)aromatic aldehydes using alkyl boron reagents

   https://doi.org/10.1039/C8SC03606C  

   Chen, Xiao-Yang; Sorensen, Erik J. (December 2018, Chemical Science)

   Transition-metal-catalyzed C–H alkylation reactions directed by aldehydes or ketones have been largely restricted to electronically activated alkenes. Herein, we report a general protocol for the Ir( iii )-catalyzed ortho C–H alkylations of (hetero)aromatic aldehydes using alkyl boron reagents as the coupling partner. Featuring aniline as an inexpensive catalytic ligand, the method was compatible with a wide variety of benzaldehydes, heterocyclic aldehydes, potassium alkyltrifluoroborates as well as a few α,β-unsaturated aldehydes. An X-ray crystal structure of a benzaldehyde ortho C–H iridation intermediate was also successfully obtained. 

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5. Synthesis of annulated rosarins via iminium activation

   https://doi.org/10.1039/D4QO01559B  

   Nguyen, Duong D; Labella, Jorge; Gómez-Gómez, Marta; Torres, Tomás; Sessler, Jonathan L (October 2024, Organic Chemistry Frontiers)

   Herein, we demonstrate that iminium activation increases the yield of expanded porphyrin synthesis by enhancing the reactivity of aldehydes used in macrocyclization. 

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