A mixture of 560 g of potassium carbonate, 700 ml of ethanol (96%), 404 g
of 1,3-dibromopropane and 260 g of ethyl acetoacetate was heated with
stirring to go 60°C. After the reaction had subsided, the reaction mixture was
refluxed for 5 hours. Then the bulk of the alcohol was distilled off under
ordinary pressure and the residue was mixed with 1.5 L of water. The
resulting oily layer was separated, and the aqueous phase was extracted with
benzene and the benzene layer was combined with the oil. After drying with
sodium sulfate the benzene was distilled off and the residue was fractionally
distilled 250 g (73% of theory) of 2-methyl-3-carbethoxy-5,6-dihydropyrane
of boiling point 105°-108°C were obtained.
140 ml of 63% hydrobromic acid were slowly added at room temperature to
128 g of 2-methyl-3-carbethoxy-5,6-dihydropyrane, and much carbon dioxidewas evolved. After standing for 1 to 2 days at room temperature the mixture
was diluted with an equal volume of iced water; the layer of dark colored oil
formed was separated, the aqueous phase was extracted with chloroform, and
the extract was combined with the oil and washed with a saturated solution of
sodium bicarbonate. The solution was dried with sodium sulfate, the
chloroform was distilled off under normal pressure, and the residue was
fractionally distilled in vacuo. 109 g (81% of theory) of 1-bromohexanone-5 of
boiling point 94°-98°C/12 mm Hg were obtained.
A solution of 10.0 g of 1-bromohexanone-5 in 100 ml of ethanol was gradually
mixed at the boil with vigorous stirring with 11.3 g of the sodium salt of
theophylline in 100 ml of water. After 3 hours refluxing the alcohol was
distilled off, and the residual aqueous phase was cooled and made alkaline
and extracted with chloroform. The chloroform solution was evaporated and
the residue re-crystallized from a little isopropanol to yield 7-(5-oxohexyl)
theophylline. MP: 75°-76°C; a yield of about 80% (calculated on the reacted
theophylline).
