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.

A new route to several hitherto unknown linearly and angularly architectured polycyclic coumarin derivatives has been developed involving tandem applications of three atom economic processes viz. Claisen rearrangement, ring-closing enyne metathesis, and Diels–Alder reactions.

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A combination of Claisen rearrangement, ring-closing metathesis, and Diels-Alder reaction is used to synthesize linearly and angularly architectured polycylic coumarin derivatives, such as (VII) and (XII). -(CHATTOPADHYAY*, S. K.; BISWAS, T.; NEOGI, K.; Chem. Lett. 35 (2006) 4, 376-377; Dep. Chem., Univ. Kalyani, Kalyani 741 235, India; Eng.) -M. Paetzel 35-178