Alkylations of tricyclo[5.2.1.0]deca-4,8-dien-3-one by a cuprate reaction

Alkylation at C₆ of tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one (R=H) was achieved by treatment of 6-bromotricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one with lithium dimethylcuprate and subsequently with an appropriate electrophile. The best results were obtained in THF as the solvent. A wide range of alkyl halides, bromo ketones and esters, and acetyl chloride resulted in C₆-tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-ones in moderate to good yields. This alkylation reaction proceeds via a C₆-carbanionic Cu intermediate, which is likely stabilized by the enone olefinic bond. 6-Bromo-endo-tricyclo[5.2.1.0^2,6]dec-8-en-3-one, which lacks this double bond, behaves differently. Treatment with lithium dimethylcuprate leads to dehydrobromination to give tricyclo[5.2.1.0^2,6]deca-2(6),8-dien-3-one in high yield.