A pentacyclic condensation product from 2,4-dimethyl-7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid

2,4-Dimethyl-7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid on preparation of a mixed anhydride, followed by reduction with sodium borohydride, affords 5,7a,13,13b-tetramethyl-2,10-dinitro-5a,7,7a,13,13a,13b-hexahydro-5H-[1,4]benzoxazino[3′,2′:4,5]pyrano[3,2-b][1,4]benzoxazine (3), the structure of which was established unambiguously by X-ray analysis.