Structural insights into methyl- or methoxy-substituted 1-(α-aminobenzyl)-2-naphthol structures: the role of C—H...π interactions

Abstract

Aminobenzylnaphthols are a class of compounds containing a large aromatic molecular surface which makes them suitable candidates to study the role of C—H…π interactions. We have investigated the effect of methyl or methoxy substituents on the assembling of aromatic units by preparing and determining the crystal structures of (S,S)‐1‐{(4‐methylphenyl)[(1‐phenylethyl)amino]methyl}naphthalen‐2‐ol, C26H25NO, and (S,S)‐1‐{(4‐methoxyphenyl)[(1‐phenylethyl)amino]methyl}naphthalen‐2‐ol, C26H25NO2. The methyl group influenced the overall crystal packing even if the H atoms of the methyl group did not participate directly either in hydrogen bonding or C—H…π interactions. The introduction of the methoxy moiety caused the formation of new hydrogen bonds, in which the O atom of the methoxy group was directly involved. Moreover, the methoxy group promoted the formation of an interesting C—H…π interaction which altered the orientation of an aromatic unit.

A combined structural and computational investigation of aminobenzylnaphthol compounds derived from the Betti reaction using valine methyl ester

“…23 First of all, in the aminobenzylnaphthols reported so far, the amino group is involved into an intramolecular hydrogen bonding with the close hydrogen atom of the naphthol group and, usually, it does not participate to other interactions. [6][7] Also in compounds 5-7, we observed this peculiar behavior. OH•••N distances and angles of a typical intramolecular hydrogen bond were measured and are reported in Table 3.…”

“…1-2 A relevant progress was obtained, when enantiopure amines were employed in the condensation. [3][4][5][6][7] In fact, aminobenzylnaphthols bearing two stereogenic centers were easily produced. [3][4][5][6][7] In a solventless truly "green synthetic process" 2-naphthol, aryl aldehydes and (S)-1-arylethylamine reacted at 60 °C to yield the corresponding (S, S)-aminobenzylnaphthols.…”

“…[3][4][5][6][7] In fact, aminobenzylnaphthols bearing two stereogenic centers were easily produced. [3][4][5][6][7] In a solventless truly "green synthetic process" 2-naphthol, aryl aldehydes and (S)-1-arylethylamine reacted at 60 °C to yield the corresponding (S, S)-aminobenzylnaphthols. [6][7] These molecules can be obtained as crystalline solids (51-68% yields), if small amounts of ethanol were added to the crude reaction mixture.…”

“…[3][4][5][6][7] In a solventless truly "green synthetic process" 2-naphthol, aryl aldehydes and (S)-1-arylethylamine reacted at 60 °C to yield the corresponding (S, S)-aminobenzylnaphthols. [6][7] These molecules can be obtained as crystalline solids (51-68% yields), if small amounts of ethanol were added to the crude reaction mixture. The stereochemical preference towards the (S, S)-stereoisomers was explained by invoking an asymmetric transformation of the second kind, 3,6 in which a more stable crystal subtracts itself to the equilibrium.…”

“…To gain more insights into this mechanism, the crystal structures of many (S, S)aminobenzylnaphthols, bearing also halogen atoms and other substituents on the aryl groups, were investigated with X-ray diffraction experiments. [6][7] Hydrogen bonds, involving the naphthol hydroxyl group networks, were observed, together with peculiar networks of many cooperating Tshaped CH••• interactions. [8][9] Only a few papers have been reported about the investigation of the bio-activity of the aminobenzylnaphthols synthesized so far.…”