Photoirradiation of 3-alkoxy-6-chloro-2-(2'-furyl) -4-0x0-4H-1 -benzopyrans 3 led to the formation of methyl 8-chloro-1 O-oxo-2-phenyl-2,3,4,1 O-tetrahydropyrano[3,2-b] [l 3 benzopyran-3-ylacetate 4.The reaction proceeds through the formation of 8-chlor0-4-phenyl-3a,4,6,11 b-tetrahydrofuro-[2'.3':4,5]pyrano[3.2-b] benzopyran-6-one 5a, which subsequently undergoes a ring contraction-ring expansion mechanism to give the cyclopropanecarbaldehyde 8 followed by its rearrangement to ketene 10 via the carbene 9 to furnish ester 4. The various intermediates have been isolated and identified, and their stereochemistry was established from their 'H NMR spectra.Conjugated enones with suitable substituents at the a-position, when subjected to photolysis, are known to undergo y-H abstractions.' The products obtained depend invariably upon the nature of the substituents present in the substrates: viz. 2alkyl-3-arylcyclohex-2-enones and 3-alkoxy-2-phenyl-4-oxo-4H-1 -benzopyrans afforded photocyclised angular products whereas 3-benzyloxy-2-styrylchromones,4 upon exposure to W light, yielded tricyclic linear products. In contrast 3methoxy-2-methylchromone has been found to lead to the formation of a novel dimeric oxetanol.' It thus became of interest to investigate the photochemistry of 3-alkoxychromones bearing a fury1 group instead of a Me, Ph or CH=CHPh at C(2), since furans themselves are known to undergo phototransformations.6 Such a system allows another dimension, here, to be studied as it becomes a bichromophoric system, an enone coupled to a furan.
Results and DiscussionThe target molecules, i.e., 2-(2'-furyl)-3a ' and 2-(5'-methyl-2'furyl)-3-benzyloxy-4-oxo-4H-1 -benzopyran 3b were synthesised as follows (Scheme 1).Photoirradiation of 3a in methanol produced ester 4, whose structure became evident from its 'H NMR and mass spectra. The 'H NMR spectrum (100 MHz) of compound 4 showed a
Synthesis of β-carboline based natural products and synthetic derivatives is one of the frontier areas of research owing to their medicinal properties.
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The search of new anticancer agents is considered as a dynamic field of medicinal chemistry. In recent years, the synthesis of compounds with anticancer potential has increased and a large number of structurally varied compounds displaying potent anticancer activities have been published. Pyrazole is an important biologically active scaffold that possessed nearly all types of biological activities. The aim of this review is to collate literature work reported by researchers to provide an overview on in vivo and in vitro anticancer activities of pyrazole based derivatives among the diverse biological activities displayed by them and also presents recent efforts made on this heterocyclic moiety regarding anticancer activities. This review has been driven from the increasing number of publications, on this issue, which have been reported in the literature since the ending of the 20th century (from 1995-to date).
β-Carboline containing alkaloids are ubiquitously present in Nature, while an imidazo[1,2-a]pyridine nucleus is incorporated in various synthetic commercial drugs and biologically previliged moieties.
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