Pyrano benzo-277-1 -pyrans

Chromans and isochromans can be obtained by the reductive Pd-catalysed Heck cyclisation of 4-(2-bromophenoxy)-2-methylbut-l-ene and 3-(2-bromobenzyloxy)-2-methylpropene respectively <07TL2307>. Bromopropyl derivatives of 3,5-dihydroxy-iodobenzene and of 3,5-dihydroxymethyliodobenzene undergo sequential intramolecular alkylations and an intermolecular Heck coupling on treatment with an acrylate under microwave irradiation and Pd-catalysis mediated by norbornene. The products are 5-alkenyl derivatives of pyrano[3,2-g]benzo-2/7-1 -pyrans and pyrano[4,3-/]bcnzo-l77-2-pyrans (Scheme 13) <07JOC775>. 

The reaction of 3-aminoprop-2-enoates with 1,4-naphthoquinone affords 5-hydroxy-benzo[g]indoles and hence offers access to pyrano[3,2-e]benzo[g]indoles that become strongly red coloured on irradiation with half-lives similar to the analogous 5,6-dimethylnaphtho-[l,2-b]pyran 14 (Scheme 19) <00WOP31080>. 

C12H12N2O6, 3,4,4aa,10aa-Tetrahydro-7,9-dinitro-2H,5H-[1]benzo-pyrano[2,3-b]pyran, 45B, 326... 

Recently, Brahmachari and his group [133] have developed a simple, facile, and convenient practical method for one-pot syntiiesis of pharmaceutically interesting diverse kind of pyran-annulated heterocycles such as 4H-pyrano[3,2-c]coumarins (14), 4H-pyrano[3,2-c]-a-pyrones (12), 5,6,7,8-tetrahydro-5-oxo-4H-chromenes (9), and benzo[//]-4H-chromenes (8) in the presence of ammonium or sodium formate as catalyst via three-component... 

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