9-Borabicyclo(3.3.1)nonane → 1,4-Dioxaspiro(4.5)dec-7-ene

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Reaction Steps

A solution of 4.50 g (20 mmoles) of 4-morpholino-3-cyclohexene-1-one ethylene ketal in 10 ml of tetrahydrofuran (THF) is added to 2.44 g (20 mmoles) of solid 9-BBN. A suspension results which becomes clear after stirring for 6 hours at room temperature. The THF is removed under reduced pressure (20 Torr) and 2 ml of methanol is added to the remaining solid. An exothermic reaction is initiated by gentle warming and results in a clear solution which is stirred. The stirring is stopped and the mixture is cooled slowly to room temperature to crystallize the by-product, B-(morpholino)-9-BBN methanol complex. The solid is triturated with n-pentane (3×30 ml) and the combined pentane layers are washed successively with water (3×10 ml), 3N sodium hydroxide (3×6 ml) and water (2×10 ml). The pentane solution is dried and the pentane is evaporated under reduced pressure (20 Torr). The residue is purified by distillation to give 2.10 g (75 percent yield based on 4-morpholino-3-cyclohexene-1-one ethylene ketal) of 3-cyclohexene-1-one ethylene ketal, boiling point, 82° C.-84° C. at 20 Torr.

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