Transesterification-dipolar cycloadditions, nitrone

The synthesis of tricyclic compound 120 was first reported by Tamura and co-workers using a tandem transesterification-cycloaddition reaction of nitrone methyl ester 118 and cyclohexen-3-ol (Scheme 16.17). This reaction was catalyzed by titanium tetrachloride to make nitrone cyclohexenyl ester 119. A subsequent 1,3-dipolar cycloaddition reaction proceeded presumably through a transition state involving the i-cis-like conformation of the ester C—O bond and the E configuration of the nitrone C=N bond (Scheme 16.17). 

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