Aromatisation in Adducts of α-Terpinene: Influence of Hindered Internal Rotations

Abstract

Each adduct of α-terpinene with p-quinone and 1,4-naphthoquinone in Ac 2 O/Et 3 N at 180 °C gives two aromatic products, one of which had a distinctive smell formed by the loss of an ethylene group. Here, we report the crystal structure of (1RS, 4RS)-1-isopropyl-4-methyl-1,4-dihydro-1,4-ethanoanthracene-9,10-diyl diacetate. It is crystallised in an orthorhombic space group, Pbca, with cell dimensions a = 10.2899 (7), b = 19.7804(9), c = 19.7519(8) Å and Z = 8. According to its NMR and X-ray diffraction data, the isopropyl and acetate groups slowly rotate.

Accurate Crystal Structures of C12H9CN, C12H8(CN)2, and C16H11CN Valence Isomers Using Nonspherical Atomic Scattering Factors

“…Comparators used in this category: NAHZAX, TIVFUZ, VAKBAK, ZIZZOX . Comparators which were obtained from the CSD, but excluded due to disorder: FALHIK, MICBUW, MICCAD, MICCEH, OCOHUL, PIBCIO, PIBCOU, PIBCUA, PIBDAH, PIBDEL, PIBDUB, RAKPUQ, WEXRIA, YOSFAP e Statistical outlier omitted from the averaged values. …”

“…Goh et al analyze this issue in detail and suggest that the disorder in these mixed ene/ane barrelene cages is due to a high similarity in crystal-packing requirements of the H 2 C-CH 2 and the HCCH staves. Uno and Mithani specifically mention this disorder but do not address it at any length, while Aotake, Tanaka, and Kaya do not mention any ene/ane disorder in the barrelene cages. Unsurprisingly, the C–C bonds of these staves, C2-C3 and C9-C10, experience the greatest distortion of the disorder.…”

“…The new single-crystal X-ray diffraction structures obtained in this work belong to four major structural categories: benzobarrelenes (1, 2) and a partially hydrogenated analogue 3, benzo-and naphthosemibullvalenes (4,11,13), benzocyclooctatetraenes (5,6,12,14), and di/tetrahydrocyclobuta[a]naphthalenes (DCBN, TCBN) (7,8,9,10). Because of the proclivity of photochemistry to produce many isomers via excited-state reactions, spread across all four categories are valence isomers with the formula C 13 H 9 N (2,4,5,6,7,8); two (11,12) are valence isomers of C 14 H 8 N 2 and two (13,14) are naphtho-rather than benzo-fused analogues of formula C 17 H 11 N. Atom labels are taken from the first exemplar (see Figure 1a) and applied to all structures for ease of comparison. The atom numbering schemes should be consulted for identifying specific entries.…”

“…There is continuing strong interest in the preparation and applications of benzobarrelenes (1,4-dihydro-1,4-ethenonaphthalenes, I in Chart ), − which are derivatives of the parent barrelene (bicyclo[2.2.2]­octa-2,5,7-triene) first reported by Zimmerman in 1960 . Benzobarrelenes are particularly suited as chelating bis-η 2 -ethene ligands for low-valent transition metals such that more than 70% of the 117 reported crystal structures in the Cambridge Structure Database (CSD, version 2021.2) are of such complexes.…”