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

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-tetracy-clopropyladamantane (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 C-2- 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 S-4-symmetric conformation for this hydrocarbon at 203 K. ((c) Wiley-VCH Verlag GmbH 1 Co. KGaA, 69451 Weinheim, Germany, 2005).