Visible light-promoted enantioselective aerobic oxidation of pyrazolones by phase transfer catalysis

Isothiourea-Catalysed Acylative Kinetic Resolution of Tertiary Pyrazolone Alcohols

The development of methods for the selective acylative kinetic resolution (KR) of tertiary alcohols is a recognised synthetic challenge with relatively few successful substrate classes reported to date. In this manuscript, a highly enantioselective isothiourea-catalysed acylative KR of tertiary pyrazolone alcohols is reported. The scope and limitations of this methodology have been developed, with high selectivity observed across a broad range of substrate derivatives incorporating varying substitution at N(2)-, C(4)- and C(5)-, as well as bicyclic constraints within the pyrazolone scaffold (30 examples, selectivity factors (s) typically >100) at generally low catalyst loadings (1 mol %). The application of this KR method to tertiary alcohols derived directly from a natural product (geraniol), alongside pharmaceutically relevant drug compounds (indomethacin, gemfibrozil and probenecid), with high efficiency (s >100) is also described. The KR process is readily amenable to scale up using bench grade solvents and reagents, with effective resolution on a 50 g (0.22 mol) scale demonstrated. The key structural motif leading to excellent selectivity in this KR process has been probed through computation, with an NC=O⋅⋅⋅isothiouronium interaction from substrate to acylated catalyst observed within the favoured transition state. Similarly, the effect of C(5)-aryl substitution that leads to reduced experimental selectivity is probed, with a competitive π-isothiouronium interaction identified as leading to reduced selectivity.

Asymmetric phase-transfer catalysis

Over the past three decades, chiral phase-transfer catalysts (PTCs) have emerged as highly successful organocatalysts in a diverse range of asymmetric reactions. A substantial number of chiral PTCs have now already been discovered and utilized in dependable routes to enantioenriched products. These extend beyond the classical cationic PTCs with the emergence of anionic phase-transfer catalysis and hydrogen-bonding phase-transfer catalysis providing new asymmetric synthetic approaches. Nevertheless, the application level of chiral PTCs in both academic and industrial processes is below our expectation. This Review highlights the notable advances in chiral PTCs, including challenges, limitations and efforts to overcome them. Following this, the potential for sustainable chiral PTCs is described with a focus on using photocatalysed, flow and electrochemical synthesis.

Enantioselective α-Trifluoromethylthiolation of Carbonyl Compounds with AgSCF3 and Trichloroisocyanuric Acid

We successfully developed an enantioselective trifluoromethylthiolation of structurally diverse carbonyl compounds. Trichloroisocyanuric acid and AgSCF3 were employed to generate active electrophilic trifluoromethylthio species in situ for asymmetric C-SCF3 bond formation. A broad variety of chiral SCF3-carbon nucleophiles (pyrazolones, β-keto esters, and β-keto amides) were obtained in excellent yields with high enantioselectivities (up to 92% ee) by Cinchona alkaloid derived squaramide catalysts. The reaction exhibits high efficiency, good enantioselectivity, and high functional group tolerance, which provided a novel and efficient way for asymmetric synthesis of trifluoromethylthiolated carbonyl compounds.

Visible-Light-Promoted Aerobic α-Thiocyanation of Carbonyl Compounds with Ammonium Thiocyanate

In the present study, we successfully developed an efficient thiocyanation of carbonyl compounds by using low-toxicity and inexpensive ammonium thiocyanate as the thiocyanate source under visible light in air (O2) at room temperature. This unified strategy is very facile for thiocyanation of various carbonyl compound derivatives (β-keto esters, β-keto amides, pyrazo-5-ones, isoxazol-5-ones, etc.). More importantly, the reaction proceeded smoothly without the addition of a photocatalyst and strong oxidant, ultimately minimizing the production of chemical waste. Furthermore, this green and sustainable synthetic chemistry can be used in the late-stage functionalization (LSF) of biorelevant compounds, which offers unique opportunities to achieve smooth and clean thiocyanation of drugs under mild reaction conditions.

Fast, highly enantioselective, and sustainable fluorination of 4-substituted pyrazolones catalyzed by amide-based phase-transfer catalysts

Highly enantioselective and sustainable fluorination of 4-substituted pyrazolones has been developed by amide-based phase-transfer catalysts.

Advances in the green synthesis and agrichemical applications of oxathiapiprolin derivatives

Oxathiapiprolin was developed with high antifungal activity and novel target protein and is used in the oomycetes control for crop protection. The structural modifications of oxathiapiprolin are summarized. The achievements and challenges in the structural modification of oxathiapiprolin are also discussed in this mini review. The outlook in this field is perspected according to our own opinion and understanding on the development of oxysterol binding protein inhibition fungicides.

Synthesis of C-1 Deuterated 3-Formylindoles by Organophotoredox Catalyzed Direct Formylation of Indoles with Deuterated Glyoxylic Acid

Direct formylation of feedstock indoles with newly developed, cost-effective deuterated glyoxylic acid as formylation agent under visible light and air (O₂) as terminal oxidant has been developed. An isatin byproduct produced from the corresponding indole reactant serves as a facilitator for the formylation process. The simple, mild, metal- and oxidant-free protocol enables the synthesis of structurally diverse C1-deuterated 3-formylindoles with broad functional group tolerance and late-stage functionalization at a high level of D-incorporation (95-99%).