ABSTRACT
As shown in Scheme 1 , u tilization of the unusual bis-nucleophilicity of 1 ,3-diene-magnesium complexes, reaction of 2 with bis-electrophiles can lead to spiro or fused bicyclic molecules, depending on the regioselectivity of the cyclization. Treatment of magnesium complexes of 1 ,2-dimethylenecyclohexane with t ,n-dibromoalkanes resulted in overall l ,2-cyclizations of the original dienes, affording spirocarbocycles in good excellent yields [4] . Scheme 1 depicts a general route for the spiro-olefin synthesis, emphasizing the reactions of 2 with 1 ,n-dibromoalkanes. Typically, 1 ,n-dibromoalkane was added to the tetrahydrofuran (THF) solution of 2 at - 78°C, producing an organomagnesium intermediate accommodating a bromo group 3. The intermediate cyclized when warmed, affording the corresponding spirocarbocycle containing an exocyclic double bond.
