The conformational analysis of 2-halocyclooctanones

Medium-sized rings: conformational preferences in cyclooctanone driven by transannular repulsive interactions

“…However, the second conformer in energy is predicted as a twisted boat chair conformer (TBC1), followed by a boat chair conformer (BC2) and a distorted crown conformer (CR1). At all the levels of theory used in this work the boat-chair conformers previously labelled 2 36 or CB-2 38 converged to the twisted boat-chair conformer TBC1, and the formerly reported crown conformation converged to the distorted crown CR1. Our computational results yielded an additional boat-boat conformation BB2, which is the highest in energy.…”

“…The conformational landscape of cyclooctanone has been the subject of some computational studies [36][37][38] , which predict several conformers within 10 kJ/mol. Previous experimental NMR data and vibrational and rotational spectroscopic studies 39 were consistent with the presence of one conformation of cyclooctanone in a boat-chair configuration.…”

Diastereoselective Additions of Allylmagnesium Reagents to α-Substituted Ketones When Stereochemical Models Cannot Be Used

“…56 The transition states that were identified are shown in Scheme 5 starting from different conformers of the ketone. The activation energies listed represent the relative energies compared to a ground-state complex of the ketone in its lowest energy conformation 42 resembling 21′. 56 The relative energies of the transition states compared to the complex changed somewhat (0−3 kcal/mol) depending upon the method used or whether the calculations were conducted in the gas phase or in solvent, but the ordering of relative energies was almost unchanged.…”

“…Purification by flash chromatography (5:95 EtOAc/hexanes) afforded ketone 5b as a light yellow oil (3.220 g, 64%). The spectroscopic data ( 1 H NMR, 13 C{ 1 H} NMR, and IR) are consistent with the data reported in literature: 42 Cyclohex-1-en-1-yl(phenyl)methanone (36). A reported procedure 81 was adapted to prepare ketone 36.…”

“…The relative stereochemical configuration of alcohol 38 was assigned by X-ray crystallographic analysis: mp = 74−76 °C; 1-Cyclopropyl-1-phenylbutan-1-ol (35a). Alcohol 35a was prepared using the representative procedure for additions of Grignard reagents to ketones using ketone 34 (70 μL, 0.5 mmol) and allylmagnesium chloride (380 μL, 2.0 M solution in THF, 0.76 mmol) at 20 °C for 16 h. Purification by flash chromatography (3:97 EtOAc/ hexanes) afforded alcohol 35a as a colorless oil (0.029 g, 30%): 1 1-Cyclohexyl-1-phenylbut-3-en-1-ol (42). Alcohol 42 was prepared using the representative procedure for additions of Grignard reagents to ketones using ketone 41 (0.099 g, 0.53 mmol) and allylmagnesium chloride (530 μL, 2.0 M solution in THF, 1.06 mmol) in THF (5 mL) at −78 °C for 30 min.…”