June 2023

A new class of organoboron complexes have been developed as heavy-atom-free triplet photosensitizers. A methodology was developed for the synthesis of an indolocarbazole–imine boron difluoride (IIBD) dye and its dimer from a 6-formylindolocarbazole. The IIBD dye was then coupled with a BODIPY dye through the C-2 or C-8 position of the latter to synthesize two dyads. Both dyads showed superior photophysical properties to those of the IIBD dyes. The relative triplet conversion efficiencies of these dyes were determined by measuring their singlet-oxygen (1O2) generation capacities. All the synthesized dyes showed high 1O2 generation compared with the BODIPY dye PM567. The dyad linked through the C-2 position of the BODIPY core showed the highest 1O2 generation efficiency, which could be useful for photodynamic therapy of cancers.

Ketones are fundamental synthons in organic synthesis due to their wide range of applications, which include natural products, pharmaceuticals, dyes, fragrances, agrochemicals, and electronic materials. In recent years, direct acylation strategies based on commercially available benchtop aryl halides and aldehydes (alkyl/aryl) have been the prime focus for the construction of alkyl-aryl/aryl-aryl ketones using palladium catalysis under eco-friendly reaction conditions. In this account, we present conceptually developed palladium-catalyzed direct acylation strategies for achieving various carbo- and heterocycles such as ketones, 2-quinolinones, phthalazines, phthalazinones, benzoxazinones, anthraquinones, indenones, and 1,3-dihydroisobenzofurans. Significantly, these direct acylation strategies have been extended to synthesize the natural product neo-lignan and biologically significant molecules such as an n-butylphthalide antiplatelet drug, pitofenone, fenofibrate, a HBV inhibitor, and a PDE-4 inhibitor. This Account will be of interest to synthetic organic chemists wishing to prepare pharmaceutical molecules and natural products.1 Introduction2 Discussion2.1 Palladium-Catalyzed Environmentally Compassionate Acylation2.2 Palladium-Catalyzed Acylations Followed by Intramolecular Aldol Condensation to Afford Indenones2.3 Acylation of Iodo-acetanilides/Iodo-phenyl Acetates: Sequential One-Pot Syntheses of 2-Quinolinones2.4 A One-Pot Diversified Synthesis of Phthalazines, Phthalazinones, and Benzoxazinones2.5 Palladium-Catalyzed Direct Acylation: A One-Pot Relay Synthesis of Anthraquinones2.6 Palladium-Catalyzed Direct Oxidative Coupling of Primary Alcohols with Iodoarenes Leading to Ketones: Application to the Synthesis of Benzofuranones and Indenones3 Conclusion

This account summarizes the Cu-catalyzed borylative functionalizations of unsaturated hydrocarbons that we have developed over the past decade. First, we focus on the regioselective hydroboration of unsymmetrical internal alkynes and 1,2-dienes. Secondly, a borylative allyl–allyl coupling using 1,2-dienes, B2pin2, and an allyl phosphate is presented. Thirdly, we introduce the boroacylation and boroformylation of 1,2-dienes by using an acid anhydride or formate, respectively, as the electrophile. Lastly, we describe the synthesis of 2-boryl-1,3-butadienes and cyclic allylborates. These reactions offer a versatile method for synthesizing a broad range of useful compounds and also provide a detailed understanding of the reaction mechanism, which could lead to the development of catalysts that are both more efficient and more selective.1 Introduction2 Hydroboration of Alkynes3 Hydroboration of 1,2-Dienes and 1,3-Dienes4 Synthesis of 2-Boryl-1,3-butadienes5 Boroallylation of 1,2-Dienes6 Boroacylation of 1,2-Dienes7 Boroformylation of 1,2-Dienes and 1,3-Dienes8 Synthesis of Cyclic Allylborates9 Conclusion and Outlook