Synthesis of bioactive polyheterocycles: Regioselective cyclisation of 5-cyclohex-2-enyl-6-hydroxy[1]benzopyran-2-one

5-Cyclohex-2-enyl-6-hydroxycoumarin (4) was synthesised in 80 % yield alongwith 4% of 7-cyclohex-2-enyl-6-hydroxycoumarin (5) by the thermal sigmatropic rearrangement of 6-cyclohex-2-enyloxycoumarin (3) in refluxing N,N-diethylaniline. Treatment of 4 with m-chloroperoxybenzoic acid in refluxing benzene for 4 h gave 8-hydroxy-7a,8,9,10,11,11a-hexahydrobenzofuro[3,2- f]benzopyran-3-one (6) in 90 % yield which was then dehydrogenated to benzofuro[3,2-f]benzopyran-3-one (7) with excess of DDQ. Compound 4 was also cyclised with pyridine hydrotribromide or hexamine hydrotribromide to 2-bromo-1,3-propano-1,2,3-trihydropyrano[3,2-f]benzopyran-8-one (8) in 88 % or 95 % yield respectively. Compound 4 when treated with cold cone. H2SO4 at 0-5 degrees C for 4 h furnished the cyclised 1,3-propano-1,2,3-trihydropyrano[3,2-f]benzopyran-8-one (10) in 90 % yield.