Conformational Studies on Oligosubstituted Adamantane Derivatives – Structural Features of Tetravinyl‐, Tetracyclopropyl‐, and Tetraisopropyladamantane

Abstract 1,3‐Diisopropyl‐ (4), 1‐tert‐butyl‐3‐isopropyl‐ (5), 1,3,5‐triisopropyl‐ (6) and 1‐tert‐butyl‐3,5‐diisopropyladamantane (7) were prepared from the same synthetic precursor – methyl 3‐isopropyladamantane‐1‐carboxylate (10) – applying a standard set of repetitive procedures in 65, 77, 24, and 34 % overall yield, respectively. 1,3,5,7‐Tetraethenyladamantane (17) was obtained in two steps – Swern oxidation and Wittig olefination – from 1,3,5,7‐tetrakis(hydroxymethyl)adamantane (15) in 45 % overall yield and converted into 1,3,5,7‐tetracyclopropyladamantane (8) by fourfold cyclopropanation with diazomethane catalyzed by palladium(II) acetate (91 % yield). Hydrogenolysis of 8 over a platinum catalyst furnished 1,3,5,7‐tetraisopropyladamantane (9) in quantitative yield. 1‐Isopropyladamantane (3) as well as the hydrocarbons 4–7 did not give any crystals suitable for X‐ray crystal structure analysis, even when using the Optical Heating and Crystallization Device (OHCD). This method was rather successful when applied to the tetravinyl derivative 17, X‐ray crystal structure analysis of which revealed an approximately C2‐symmetric conformation in the solid state at 150 K. However, no well‐defined orientation was detected for the cyclopropyl groups in 8, and the molecules were severely disordered even at 30(1) K. In contrast to this, X‐ray crystal structure analysis of the tetraisopropyl derivative 9 revealed an S4‐symmetric conformation for this hydrocarbon at 203 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)