Conformational investigation of 1,8-disubstituted naphthalenes as solutes by Kerr effect and dipole moment methods

Correlated Rotations and Unusual Fluorescence Properties ofperi-Substituted, Axially Chiral Naphthyl Ketones

“…Whereas, in amides, the pyramidal ground state of the peri-(dimethylamino) group is stabilized because of the amide dipole, the electrostatic repulsion from the electron pairs at the oxygen atom destabilizes the tetrahedral ground state of the amino group of the ketones (Figure 7a). [15,18] The rotation of the carbonyl group from the ground state of the M enantiomer (GS M ) into the peri area (TS 1 ) increases the electrostatic repulsion between the free electron pairs at the amino and carbonyl groups (Figure 7b). Subsequent inversion of the amino group reduces the electrostatic repulsion at the cost of a higher steric hindrance of Me B (TS 2 ).…”

“…Figure 7. a) The ground state in amides is stabilized, the amide group is twisted out of the naphthalene plane by 112°and the lone pair of the nitrogen is directed towards the amide carbon atom; the electrostatic repulsion from the free electron pairs at the oxygen atom causes a destabilization of the tetrahedral amino group in ketones, the carbonyl group is twisted by 120°, and the lone pair of the nitrogen atom is directed toward the alkyl substituent; [18] b) interconversion of the enantiomers via pseudo-rotation and inversion of the tetrahedral amino group (see text); c) in a complete inversion, greater steric hindrance would partly compensate the weaker electrostatic repulsion; therefore, a trigonal-planar transition state (TS 5 ) is suggested; a planarization of the pyramidal NMe 2 group in the transition state to trigonal-planar would reduce the steric and electrostatic hindrance and additionally allow a larger peri distance Both the pseudo-rotationϪinversion and the proposed mechanism above avoid an energetically very costly transition state distortion of the naphthalene plane, which has been found for 1,8-(di-tert-butyl)naphthalenes. X-ray structure analyses [21] showed that the two benzene planes in 1,8-(di-tert-butyl)naphthalenes are significantly twisted by 43.4°i n the ground state, which means that these molecules are chiral.…”

“…1-Cyano-8-(dimethylamino)naphthalene (8) was synthesized from 8-amino-1-bromonaphthalene (11). [18,30] Firstly, 8-amino-1-bromonaphthalene was methylated with dimethyl sulfate by a standard method; [31] then the cyano compound 8 was obtained using CuCN in a Rosenmund-von-Braun reaction.…”

“…A nonplanar orientation, relative to the naphthalene plane, of the substituents in perisubstituted naphthyl ketones and carboxamides was also shown by a combination of Kerr effect and dipole moment methods. [18] [15] the exocyclic bonds are displaced above and below the naphthalene plane and the rotors are perpendicular to the main plane; the donor (nucleophile) is splayed inward into the peri area towards the acceptor (electrophile), which in turn is pushed outward against H 2 ; the NMe 2 group is pyramidal and the free electron pair is directed towards the carbon atom of the carbonyl group because of the repulsion of the free electrons at the oxygen atom; the carbonyl plane is small, but significantly distorted by electrostatic interactions; this has been called a ''frozen'' state of the beginning of a nucleophile addition to a carbonyl group This raises key questions. How does the electrostatic interaction influence the rotation barriers?…”

Atropisomeric diastereoisomers from nucleophilic attack on 8-acyl-1-naphthamides

“…13 Barriers to interconversion of naphthalenes bearing meta-substituted phenyl 14, 15 or pyridyl [16][17][18] rings at the 1-and 8-positions are much lower, and these compounds do not exist as atropisomeric diastereoisomers. The conformation 19,20 and racemisation 21 of enantiomeric atropisomers of 8-substituted-1-naphthamides and their thioamide derivatives 22 have been described by Mannschreck and Kiefl, but there are no reported examples of diastereoisomeric non-biaryl atropisomers based on a 1,8disubstituted naphthalene system.…”