Synthesis of Quinazoline and Quinazolinone Derivatives via Ligand-Promoted Ruthenium-Catalyzed Dehydrogenative and Deaminative Coupling Reaction of 2-Aminophenyl Ketones and 2-Aminobenzamides with Amines

The in situ formed ruthenium catalytic system ([Ru]/L) was found to be highly selective for the dehydrogenative coupling reaction of 2-aminophenyl ketones with amines to form quinazoline products. The deaminative coupling reaction of 2-aminobenzamides with amines led to the efficient formation of quinazolinone products. The catalytic coupling method provides an efficient synthesis of quinazoline and quinazolinone derivatives without using any reactive reagents or forming any toxic byproducts

Ruthenium Catalyzed Deaminative Coupling Reaction of Amines Via C-N Bond Activation

C–N bond activation via transition-metal catalyst has attracted much attention during the past two decades. This strategy has become one of the most promising way to generate secondary amines, which are very important in a broad spectrum of applications in pharmaceutical industry, synthetic organic chemistry and material science. The secondary amines can be utilized as an important synthetic intermediate for further manipulations. The in-situ formed catalytic system generated from the tetranuclear Ru–H complex with 4-(1,1-dimethylethyl)-1,2-benzenediol ligand was found to be effective for the synthesis of secondary amines from the direct deaminative coupling of amines. The ruthenium catalyst was highly effective for promoting selective coupling of two different primary amines to afford the formation of unsymmetric secondary amines. The treatment of aniline-d7 with 4-methoxybenzylamine led to the coupling product with significant deuterium incorporation on CH2 (18% D). The most pronounced carbon isotope effect was observed on the α-carbon isolated from the coupling reaction of 4- methoxybenzylamine. Hammett plot was constructed from measuring the rates of 4- methoxyaniline with a series of para-substituted benzylamines 4-X-C6H4CH2NH2 (X = OMe, Me, H, F, CF3). (ρ = -0.8±0.1). A plausible mechanistic scheme has been proposed for the coupling reaction on the basis of these results. The catalytic coupling method provides a simple and chemoselective synthesis of secondary amine products without using any reactive reagents or forming wasteful byproducts

Scope and Mechanistic Studies of Ruthenium Catalyzed C-N Bond Activation Reactions

Primary aliphatic amines which are ubiquitous in natural products, traditionally considered as inert to substitution reactions. Recent studies clearly demonstrated that the aliphatic deaminative coupling chemistry can be used to make valuable scaffolds through C–N bond activation on transition metal complexes. The catalytic system generated in situ from the tetranuclear Ru–H complex with a catechol ligand (2-9/2-16) and independently synthesized ruthenium catecholate complex 2-11 was found to be effective for the direct deaminative coupling of primary amines. The catalytic system formed in-situ from the reaction of cationic Ru–H complex 2-10 with 3,4,5,6-tetrachloro-1,2-benzoquinone 2-12 was found to mediate a regioselective deaminative coupling reaction of ketones with amines to form the -alkylated ketone products. The monitoring of the coupling reaction of acetophenone and 4-methoxybenzylamine showed a rapid formation of PhC(Me)=NCH2C6H4-4-OMe, which was slowly converted to the alkylation product. The Hammett plot obtained from the reaction of para-substituted imines showed a strong promotional effect by the amine substrates with electron-releasing group (ρ = -0.96 ± 0.1), while the analogous plot obtained from the reaction of para-substituted imines with benzylamine showed a moderate promotional effect from the ketone substrates with electron-withdrawing group (ρ = +0.24 ± 0.1). The most significant carbon isotope effect was observed on the -carbon of the alkylation product (C = 1.020). The empirical rate law was determined as rate = kobs[imine][Ru] from measuring the kinetics of the alkylation reaction of the isolated imine substrate. A catalytically active Ru-catecholate complex was synthesized and the DFT study revealed a stepwise mechanism of the [1,3]-carbon migration step via the formation of a Ru(IV)-alkyl species. A plausible mechanism of the catalytic alkylation reaction via an intramolecular [1,3]-alkyl migration of Ru-enamine intermediate has been proposed. The in situ formed ruthenium catalytic systems (2-10/2-16), (2-10/2-12) and the complex 2-11 was also found to be highly selective for the dehydrogenative/deaminative coupling reactions to form number of pharmaceutically important nitrogen heterocyclic products with amines. The catalytic coupling method provides an operationally simple and chemoselective synthetic protocol without using any reactive reagents or forming wasteful byproducts

Synthesis of Symmetric and Unsymmetric Secondary Amines from the Ligand-Promoted Ruthenium-Catalyzed Deaminative Coupling Reaction of Primary Amines

The catalytic system generated in situ from the tetranuclear Ru–H complex with a catechol ligand (1/L1) was found to be effective for the direct deaminative coupling of two primary amines to form secondary amines. The catalyst 1/L1 was highly chemoselective for promoting the coupling of two different primary amines to afford unsymmetric secondary amines. The analogous coupling of aniline with primary amines formed aryl-substituted secondary amines. The treatment of aniline-d7 with 4-methoxybenzylamine led to the coupling product with significant deuterium incorporation on CH2 (18% D). The most pronounced carbon isotope effect was observed on the α-carbon of the product isolated from the coupling reaction of 4-methoxybenzylamine (C(1) = 1.015(2)). A Hammett plot was constructed from measuring the rates of the coupling reaction of 4-methoxyaniline with a series of para-substituted benzylamines 4-X-C6H4CH2NH2 (X = OMe, Me, H, F, CF3) (ρ = −0.79 ± 0.1). A plausible mechanistic scheme has been proposed for the coupling reaction on the basis of these results. The catalytic coupling method provides an operationally simple and chemoselective synthesis of secondary amine products without using any reactive reagents or forming wasteful byproducts

Biodiversity Assessment of Paddy Field Ecosystem using Birds as a Biodiversity Indicator

Biodiversity assessment is considered in making decisions concerning declaration ofprotected areas, management of nature reserves and assessment of the success ofmanagement decisions within a particular area. Biodiversity indicators are used as measuresof biodiversity. Degree of disturbance or fragmentation of a definite habitat can be measuredusing specific indicator species. A variety of invertebrates and vertebrates are widely used asindicators of biodiversity. Birds are one of the best species for the national and internationalbiodiversity schemes to be used as a biodiversity indicator.This study focused on the use of birds as an ecological indicator to assess the paddy fieldecosystem. The study was carried out in a minor irrigation system in Awlegama AgrarianService area in Wariyapola Divisional Secretariat. Bayawa was the selected tank with nearlya 38 ha of command area. A standard fixed-radius point count method with the radius set at25 m was used to sample birds in the paddy field ecosystem. Shanon index was used toexplain the results. During a single rice cycle, rice plants undergo three main phenologicalstages namely; vegetative, reproductive and ripening. All these stages are influenced byfarming practices such as tillage, irrigation, crop establishment, agrochemical application andweeding. Different stages with different farming practices create distinct habitats for variousbird species. According to the results, the highest Shanon index value (highest diversity) wasrecorded during the vegetative stage. Birds‟ diversity had a significant, strong (p=0.05)negative correlation with the age of the paddy. Initial land preparation and vegetative stagesprovide more food sources for the predatory birds who feed on worms, insects and snails;some of whom act as pests of paddy. Mixing of upper and the sub-soil layers in landpreparation stages supply more feed for predatory birds. Cattle Egret, Red Wattled Lapwing,Intermediate Egrets, Indian Pond Heron, Black Necked Stroke were in abundance at landpreparation and vegetative stage. Yellow crowned woodpecker and White throated muniawere recorded during the later stages. A variety of management practices such as landpreparation, crop establishments, irrigation, nutrient and pest management, harvesting withinthe paddy field facilitate to create different habitats with different eco systems and suitablefood for bird species. The birds as a biodiversity indicator, symbolise the ecosystem and itreflects the existing condition of an ecosystems. A detailed study will reveal how these birdswould help to manage different pests in the paddy fields to bring benefits to the farmers.Keywords: Biodiversity indicator, Ecosystem, Paddy field, Birds, Cattle Egre