A synthetic strategy based on tandem application of Claisen rearrangement and intramolecular Heck reaction as key steps has been developed for the synthesis of various hitherto unknown benzoxocine-and benzoxonine-fused coumarin and quinolone derivatives.Various normal-ring-size heterocycle-fused heterocyclic systems display interesting properties and there has been a continuous evolution of newer methodologies for the synthesis of such ring systems. 1 In contrast, medium-ring heterocycle-annulated heterocyclic systems are less known until recently when various metal-catalysed organic transformations made medium-sized rings more accessible. 2 The palladium-catalysed intramolecular Heck-type arylation reaction has been extensively used for the synthesis of heterocyclic rings of varying size and complexity. 3 However, medium-ring formation through such a procedure still poses challenges and therefore remains as an explorable exercise. Whereas with activated olefins (Michael-type olefinic fragments) only one mode of cyclisation (electronic controlled) is mostly observed, 4 mixtures of endo-and exo-cyclisation products are usually formed 5 during medium-sized-ring formation from intramolecular Heck reaction with unactivated olefins. 6 This difference in regioselectivity has been explained by the difficulties associated with the attainment of coplanar eclipsed orientation of the relevant moieties during the carbopalladation step ( Figure 1). However, with the increase in chain length exclusive endo-cyclisation leading to nine-or ten-membered heterocyclic rings has also been observed. 7
Figure 1We have been engaged for some time in the synthesis of medium-ring heterocycle-fused heterocyclic systems culminating in the development of synthetic routes to hitherto unknown oxepin-and oxocin-fused coumarins, 8 quinolones, 9 carbazole 10 and naphthalene derivatives, 11 based on tandem applications of Claisen rearrangement and ring-closing diene-or enyne metathesis. 12 The methodology has found application 13 in the synthesis of other medium-ring heteroannulated compounds. Herein, we report 14 a new methodology for the synthesis of mediumring oxacycle-annulated heterocycles based on tandem Claisen rearrangement 15 and Heck-type arylation reaction as key steps. In view of the known importance of furo-and pyranocoumarins 16 and their isosteric analogues furo-and pyrano-2-quinolones 17 we have chosen coumarin and 2-quinolone as the heterocyclic frameworks for the exploration in the present study.
An efficient construction of the entire carbon skeleton of the novel polyoxazole-based natural product IB-01211 was developed which featured a biomimetic macrocyclisation of an w-amino acid tethered through two bisoxazole units as the key step.
Chronic arsenic toxicity (arsenicosis) as a result of drinking arsenic-contaminated groundwater is a major environmental health hazard throughout the world, including India. During the last four decades arsenic contamination of groundwater in nine districts out of twenty in West Bengal has become a serious problem. About 20% population of West Bengal in nine districts (Malda, Murshidabad, Nadia, North 24- Parganas, and South 24-Parganas, Kolkata, Howrah, Hooghly and Burdwan) are affected by arsenic problem. To prevent this harmful effect, every people need to have proper knowledge and positive attitude towards arsenic. In this study, the researcher constructed a standardized tool of knowledge and attitude towards arsenic to assess the knowledge and attitude level of arsenic among the people of arsenic contaminated area. The researcher took item analysis method to assess the quality of the items of every section. Then the tools were measured the reliability by the Pearson’s product moment correlation method. Primarily two self-administered tools of 39 knowledge items and 32 attitude items regarding arsenic was applied among the people of Nadia district of West Bengal. Therefore, the researcher analyzed the collecting data and eliminated the poor items on the basis of difficulty value and discrimination index. After elimination of distracting items, 25 items in knowledge section and 25 items in the attitude section were retained as a final form of tool regarding arsenic. Thereafter the final form of tools applied among 60 general people to calculate the reliability of the tools by test-retest reliability method. The researcher found significant reliability in knowledge and attitude tools. These standard tools can assess the knowledge and attitude level regarding arsenic among the people of arsenic contamination area with accuracy.
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