Effect of methoxyl groups on the NMR spectra: configuration and conformation of natural and synthetic indanic and tetralinic structures.

Here, we studied the influence of the methoxyl groups attached at C-7 and C-2' of natural and synthetic 1-arylindanes on the chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J1,2 coupling constants. This influence was also analysed in natural 1-aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C-8 and C-2'. The methoxyl groups attached at C-7 in indanes or at C-8 in tetralins produce a deshielding signal at H-1 and shield at C-1 and a strong decrease in the value of J1,2 due to the pseudoequatorial location adopted by the aryl group bound at C-1, avoiding an 'A1,3 strain'. Furthermore, compounds with hydroxyl or methoxyl groups in C-2', in the absence of substituents of C-7 or C-8, present a strong deshielding signal at H-1, strong shield of the C-1 signal and a decrease in the value of J1,2 . This is attributed to the stereoelectronic effects of the methoxyl or hydroxyl groups, which we have called 'Asarone effect'. NOESY experiments were conducted to confirm the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A1,3 strain and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using 1 H-NMR and 13 C-NMR spectra. Copyright © 2016 John Wiley & Sons, Ltd.

Tetrameric aggregate of 1,c-3-diphenyltetran-r-1-ol via an R4(4)8 homodromic ring.

The compound 1,c-3-diphenyltetran-r-1-ol (systematic name: 1,c-3-diphenyl-1,2,3,4-tetrahydro-r-1-naphthol), C(22)H(20)O, which possesses the tetrahydronaphthalene core that is found in a large number of natural products, crystallizes with Z' = 4 and with the four molecules forming a hydrogen-bonded cyclic aggregate. The aliphatic six-membered rings are present with two different conformations in the molecules of the asymmetric unit. A comparison with similar fragments reveals their conformational flexibility. In addition, the structure demonstrates the relative stereochemistries of the chiral centers, which are important since the title compound is used in the stereoselective synthesis of compounds with therapeutic activity.