54867-18-4Relevant academic research and scientific papers
Ring-chain tautomerism of 2-aryl-substituted cis- and trans-decahydroquinazolines
Lazar, Laszlo,Goeblyoes, Aniko,Martinek, Tamas A.,Fueloep, Ferenc
, p. 4734 - 4741 (2002)
In CDCl3 at 300 K, 2-aryl-substituted cis- and trans-3-isopropyldecahydroquinazolines and trans-3-phenyldecahydroquinazolines proved to be three-component (r1-o-r2) ring-chain tautomeric mixtures, whereas only ring-closed tautomers could be detected for the 3-methyl-substituted analogues. The proportions of the ring-chain tautomeric forms at equilibrium were strongly influenced by the N-substitutents and the cis-trans ring junction and could be described by the equation log Kx = ρσ + log Kx=H. These are the first examples among 2-aryl-1,3-N,N-heterocycles of a three-component ring-chain tautomeric equilibrium characterized by a Hammett-type equation. The stabilities of the ring-closed forms of cis- and trans-2-aryldecahydroquinazolines and the corresponding 3,1-benzoxazines were found to increase in the following sequence of the heteroatom at position 3: NPh N-i-Pr O NMe.
EXPERIMENTAL STUDIES OF THE ANOMERIC EFFECT. PART 2 RING INVERSION AND NITROGEN INVERSION EQUILIBRIA IN CIS-DECAHYDROQUINAZOLINES
Booth, Harold,Khedhair, Khedhair A.,Al-Shirayda, Hatif A. R. Y.
, p. 1465 - 1476 (2007/10/02)
The positions of conformational equilibria due to the double ring inversion in cis-decahydroquinazoline (7-->//07-->8 1.08 kcal mol-1; -ΔG09-->10 1.10 kcal mol-1) for the conformation which would allow the lone pairs on N(1) and N(3) to lie on the hindered 'inside' face of the molecules.However, the values of 3J(CHNH) coupling constants for both cis-decahydro-3-methylquinazoline (10) and cis (4aH, 8aH) cis (2H, 8aH)-decahydro-2,3-dimethylquinazoline (14) show that the N-inversion equilibrium at N(1) prefers the conformation in which N(1)-H is 'inside' (axial), and N(1)-lone pair equatorial, thus demonstrating the ability of the anomeric effect to outweigh steric repulsions.
