Molecular Editing of Pyrroles via a Skeletal Recasting Strategy

Heterocyclic scaffolds are commonly found in numerous biologically active molecules, therapeutic agents, and agrochemicals. To probe chemical space around heterocycles, many powerful molecular editing strategies have been devised. Versatile C-H functionalization strategies allow for peripheral modifications of heterocyclic motifs, often being specific and taking place at multiple sites. The past few years have seen the quick emergence of exciting "single-atom skeletal editing" strategies, through one-atom deletion or addition, enabling ring contraction/expansion and structural diversification, as well as scaffold hopping. The construction of heterocycles via deconstruction of simple heterocycles is unknown. Herein, we disclose a new molecular editing method which we name the skeletal recasting strategy. Specifically, by tapping on the 1,3-dipolar property of azoalkenes, we recast simple pyrroles to fully substituted pyrroles, through a simple phosphoric acid-promoted one-pot reaction consisting of dearomative deconstruction and rearomative reconstruction steps. The reaction allows for easy access to synthetically challenging tetra-substituted pyrroles which are otherwise difficult to synthesize. Furthermore, we construct N-N axial chirality on our pyrrole products, as well as accomplish a facile synthesis of the anticancer drug, Sutent. The potential application of this method to other heterocycles has also been demonstrated.

Experimental and Theoretical DFT Investigations in the [2,3]-Wittig-Type Rearrangement of Propargyl/Allyl-Oxy-Pyrazolones

Here we report the synthesis of interesting 3-alkyl-4-hydroxy-1-aryl-4-(propa-1,2-dienyl)1H-pyrazol-5(4H)-ones and 9-alkyl-7-aryl-1-oxa-7,8-diazaspiro[4.4]nona-3,8-dien-6-ones, starting from 1,2-diaza-1,3-dienes (DDs) and propargyl alcohol. The reaction proceeds through a sequence Michael-type nucleophilic attack/cyclization/[2,3]-Wittig rearrangement. In the same way, the reaction between the aforementioned DDs and allyl alcohol furnished 4-allyl-4-hydroxy-3-alkyl-1-aryl-1H-pyrazol-5(4H)-ones. A DFT study was also carried out, in order to have decisive clarifications about the mechanism.

Effects of environmental factors on nitrofurantoin photolysis in water and its acute toxicity assessment

Pharmaceuticals have special attention of researchers over the world due to their possible effect on the environment and humans. This paper focuses on the photolysis of nitrofurantoin in different water matrices. Nitrofurantoin photodegradation has been indicated as a pseudo-first order photoreaction. The indirect photodegradation rate of nitrofurantoin (river water, k₁ = 0.0088 min^-1 and synthetic wastewater, k₁ = 0.0154 min^-1) was slower than its direct photolysis rate (ultrapure water, k₁ = 0.0176 min^-1). The highest value of quantum yield of nitrofurantoin photodegradation (ϕ = 0.2047) was observed at pH = 4, while at higher pH-values it decreased. Furthermore, the mechanism of nitrofurantoin photodegradation is proposed. Heterocyclic ring opening and further hydrolysis, nucleophilic aromatic photosubstitution and homolytic N-N bond cleavage are suggested as three main initial processes of nitrofurantoin photodegradation. Acute toxicity study of nitrofurantoin and its photoproducts with regard to luminescence inhibition of Vibrio fischeri showed that the toxic effect of nitrofurantoin (EC₅₀ = 4.0 mg L^-1) decreases by photolysis.