K. Rajendar Reddy

Ultrasonic and Microwave-Assisted Synthesis of β-Nitro Styrenes and Nitro Phenols with Tertiary Butyl Nitrite under Acid-Free Conditions

Abstract Tertiary butyl nitrite (TBN) is an acid-free and safe nitrating agent that provides preferentially β-nitrostyrenes with cinnamic acids and corresponding nitro derivatives with phenols in good yields under classical conditions. However, ultrasonic and microwave-assisted reactions reduced the reaction times substantially and enhanced the yields from good to excellent. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT

Oxalylchloride/DMF as an Efficient Reagent for Nitration of Aromatic Compounds and Nitro Decarboxylation of Cinnamic Acids in Presence of KNO3 or NaNO2 Under Conventional and Nonconventional Conditions

Nitration of aromatic compounds and cinnamic acids with oxalylchloride/DMF afforded the corresponding nitro derivatives in the presence of KNO3 or NaNO2 under conventional and nonconventional (ultrasonic and microwave) conditions. The present methodology offers several benefits such as excellent yields, simple work-up procedure, and short reaction times. The yields obtained under present methodology are comparable with those obtained from (POCl3/DMF/KNO3 or NaNO2) and (SOCl2/DMF/KNO3 or NaNO2) systems followed by shorter reaction times. The reaction times of sonication and microwave conditions are very shorter than those of the conventional conditions.

Ammonium metavanadate/thiocyanate-triggered electrophilic thiocyanation of aromatic and heteroaromatic compounds in aqueous bisulfate and acetonitrile media

The ammonium metavanadate/thiocyanate system is used as an efficient reagent for regioselective thiocyanation of aromatic and hetero aromatic compounds under conventional and nonconventional conditions such as ultrasonically assisted and microwave-assisted reactions. The reactions proceeded smoothly and afforded good yields of products with high regioselectivity. Longer reaction times (about 8 h) observed under conventional conditions were reduced to 0.5 h/30 min under sonication and to 90 s in the case of microwave-assisted reactions. GRAPHICAL ABSTRACT

Vanadium Pentoxide as a Catalyst for Regioselective Nitration of Organic Compounds under Conventional and Nonconventional Conditions

Vanadium pentoxide is used as an efficient catalyst for regioselective nitration of aromatic compounds under conventional and nonconventional conditions such as ultrasonically assisted (USAR) and microwave-assisted reactions (MWAR). The reactions underwent smoothly and afforded good yields of products with high regioselectivity. Observed longer reaction times (about 8 h) in V2O5 catalyzed reactions reduced to (0.5/30 min) under sonication and (90 s) in the case of MWAR. When ortho position is blocked, para derivatives are obtained as end products while ortho nitro products are obtained when para position is blocked.

Ultrasonic and microwave effects in polyethylene glycol-bound metal nitrate initiated nitration of aromatic compounds under acid free conditions

ABSTRACT Ultrasonic and microwave-assisted practical methods have been developed for the nitration of phenols using metal nitrates in aqueous polyethylene glycol (PEG) media. Solvent is recycled three times for reproducibility. It was recycled with minimum loss and decomposition. Developed protocols were cost effective, simple and efficient, which afforded nitration products in good to excellent yields. The observed hyperchromic/hypochromic shifts in the UV/VIS spectra of metal nitrates in PEG solutions could be due to the plausible in situ formation of “PEG-bound M(II) nitrate” and thereby the release of nitronium ion () during the course of reaction when metal nitrate [M(II)nitrate] is added to PEG. Nitronium thus formed most likely is captured by aromatic compound to afforded nitro aromatics.

Kinetic and Mechanistic Study of Transition Metal Ion Catalyzed Vilsmeier–Haack Cyclization and Formylation Reactions with Acetanilides

Vilsmeier–Haack reactions (VHR) with acetanilides afforded 2-chloro 3-formyl quinoline derivatives. The reactions obeyed second order kinetics with a first order dependence on VHR as well as acetanilide. Significant rate enhancements were observed when transition metal ions such as Cu(II), Ni(II), Co(II), and Cd(II) were used as catalysts in these reactions. The kinetic results in transition metal ion catalyzed reactions coupled with uv-visible spectrophotometric observations substantiated the participation of mixed ligand precursors of the type [M(II)S(VHR)] involving acetanilides and VH reagents in the rate limiting step. Activation parameters were computed and interpreted suitably.

Cesium carbonate as efficient catalyst for chemoselective transesterification of β-ketoesters under conventional and unconventional conditions

Transesterification of β-ketoesters with different alcohols has been studied under conventional and unconventional conditions using the simple desktop chemical cesium carbonate as catalyst. These methods enabled transesterification of β-ketoesters in good yields with dramatic rate acceleration and reduced reaction times. The procedures which used unconventional methods, for example sonication and microwave irradiation, are highly promising compared with conventional procedures.Graphical AbstractScheme 1 General Equation for a transesterification reactionScheme 2 Transesterification of β-ketoesters

Isoquinolinium Dichromate and Chlorochromate as Efficient Catalysts for Oxidative Halogenation of Aromatic Compounds Under Acid-Free Conditions

Isoquinolinium dichromate and isoquinolinium chlorochromate were found as efficient catalysts to trigger oxidative bromination and iodination of aromatic hydrocarbons with KBr/KI and KHSO4 under acid-free conditions. Reaction times reduced highly significantly under sonication, followed by corresponding mono bromo derivatives in very good yield with high regioselectivity.

Transition Metal Ions as Efficient Catalysts for Vilsmeier–Haack Formylation of Hydrocarbons with Reagents: Kinetics and Mechanism

The Vilsmeier–Haack formylation reactions with hydrocarbons are sluggish in acetonitrile medium. The VH reactions follows second-order kinetics and affords formyl derivatives under kinetic conditions that are also irrespective of the nature of the oxychloride (POCl3 or SOCl2) used for the preparation of VH reagent along with DMF. However, the reactions undergo significant rate accelerations in the presence of transition metal ions such as Cu(II), Ni(II), Co(II) and Cd(II). Transition metal ion catalyzed VH formylation is explained through the formation of a mixed ligand complex of the [M(II)S(VHR)] type prior to the rate determining rearrangement step, before yielding formyl derivatives of hydrocarbons.