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Exhaustive One‐Step Bridgehead Methylation of Adamantane Derivatives with Tetramethylsilane

par Bonsir, Maxime ;Davila, Christian;Kennedy, Alan Robert;Geerts, Yves
Référence European Journal of Organic Chemistry, 2021, 37, page (5227-5237)
Publication Publié, 2021-10-01

Article révisé par les pairs

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Résumé :

A methylation protocol of adamantane derivatives was investigated and optimized using AlCl3 and tetramethylsilane as the methylation agent. Substrates underwent exhaustive methylation of all available bridgehead positions with yields ranging from 62 to 86 %, and up to six methyl groups introduced in one step. Scaling-up of the reaction was demonstrated by performing the >40 gram-scale synthesis of 1,3,5,7-tetramethyladamantane with 62 % yield. For several substrates, rearrangements were observed, as well as cleavage of functional groups or Csp3−Csp2 bonds or even cyclohexyl-adamantyl bonds. Based on mechanistic studies, it is suggested that a reactive methylation complex is formed from tetramethylsilane and AlCl3. X-ray diffraction structures of hexamethylated bis-adamantyls reveal elongation or widening of sp3 carbon bonds between adamantyl moieties to 1.585(3) Å and 125.26(9)° due to repulsive H⋅⋅⋅H contacts.