Exhaustive One‐Step Bridgehead Methylation of Adamantane Derivatives with Tetramethylsilane

Abstract

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.

Synthesis and Structural Properties of Adamantane‐Substituted Amines and Amides Containing an Additional Adamantane, Azaadamantane or Diamantane Moiety

“…Additionally, knowing that diamondoids are bulky and rigid fragments, one could expect to observe sterically‐induced structural features such as lengthened bonds or widened angles in the molecular structure, as we have also recently demonstrated with methylated bis‐adamantyls. [ 33 , 34 ] Therefore, we desired to elucidate the crystal structure of the amides and amines by single‐crystal X‐ray diffraction. Unfortunately, we were only able to obtain and solve the crystal structure of compounds 21 b and 22 a .…”

“…Studying the way molecules are arranged relative to each other might shine light on the behavior of the compounds during the transformation into nanodiamonds. Additionally, knowing that diamondoids are bulky and rigid fragments, one could expect to observe sterically‐induced structural features such as lengthened bonds or widened angles in the molecular structure, as we have also recently demonstrated with methylated bis‐adamantyls [33,34] . Therefore, we desired to elucidate the crystal structure of the amides and amines by single‐crystal X‐ray diffraction.…”

Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

“…With the introduction of four methyl groups in the presence of AlCl 3 , adamantane underwent fourfold methylation of all bridgehead carbons. 581 …”

“…With the introduction of four methyl groups in the presence of AlCl3, adamantane underwent fourfold methylation all bridgehead carbons. [581] As is well known, Friedel-Crafts alkylations can generate mixtures of substitution products, and the selective introduction of aryl groups at the 1,3,5,7-positions of 1012 requires precise control of reaction conditions. In 1968, Stetter and Krause employed a two-step process to add phenyl groups to the adamantane molecule, resulting in the synthesis of 1,3,5,7-tetraphenyladamantane (1016, Scheme 5).…”