Stereochemistry of seven-membered heterocycles. Communication 14. Synthesis and three-dimensional structure of 4-methyl-1,3-dioxa-5,6-benzocycloheptenes

1. On the basis of data obtained by the dipole moment method, cis-2-methyl (or phenyl)-4-methyl-1,3-dioxa-5,6-benzocycloheptenes have an equilibrium of chair and twist forms that is close in quantitative respects to the related 2-R-phthalyacetals; the spiroketal of cyclohexanone is realized in the e-Tw form; the methylal is conformationally inhomogeneous. 2. The isomeric 2-tert-butyl-4-methyl-1,3-dioxa-5,6-benzocycloheptenes, according to13C NMR data, are realized in chair conformations. An analysis has been made of the influence of the 4-methyl group on the chemical shifts of the carbon atoms of the seven-membered ring. © 1985 Plenum Publishing Corporation

The inversion of correlation between γ-effect values and dihedral angle: nontraditional chairboat conformational equilibrium in seven- and eight-membered dithioacetals

13C NMR γ-anti effect data versus dihedral angle RCXC (X=O, S; R=Me, Ph, t-Bu) in a series of six eight-membered cyclic acetals and dithioacetals are summarized. The inversion of Lambert's correlation, determined for carbocycles, has been derived. X-Ray data for chair and boat forms of eight-membered cyclic dithioacetals is presented and the equilibrium of these structures is discussed. © 1989

Stereochemistry of seven-membered heterocycles. Communication 18. Graphic processing of dipole moments of cis-2-ARYL-4-R-1,3-Dioxa-5,6-benzocycloheptenes and conformational characteristics of the 4-methyl group

1. By graphic processing of the dipole moments of cis-2-aryl-4-R-1,3-dioxa-5,6-benzo-cycloheptenes replacement of the H atom by Me(Ph) at C-4 was shown not to change the position of chair-twist equilibrium. 2. The chair-chair conformational energy and the enthalpy component of the Ce~Te conformation energy for the 4-methyl group were determined. © 1986 Plenum Publishing Corporation

Raman spectra and conformations of 2,2-dialkyl-1,3-dithio-5,6-benzocycloheptenes: coexistence of chair, boat and twist-boat forms

Raman spectroscopy has been applied to the title compounds; dithiaketals of acetone, methyl-ethylketone, ethylketone, pinacolone, cyclohexanone and fluorenone. A three-component chair⇋boat⇋twist-boat boat conformational equilibrium has been established for all compounds studied except the pinacolone derivative, which exhibits a two-component chair⇋boat equilibrium. Questions concerning the symmetry of the conformations based on depolarization data are discussed. © 1992

Stereochemistry of seven-membered heterocycles. Communication 17. PMR spectra and conformation of 2-methyl-2-phenyl-1, 3-dioxa-5,6-benzocycloheptene and its isomeric 4-methyl derivatives

1. 2-Methyl-2-phenyl-1,3-dioxa-5,6-benzocycloheptene and its isomeric 4-methyl-substituted derivatives exist in the twist conformation. 2. In the PMR of these compounds the benzyl protons and 4-methyl groups are coupled and the screening influence of the 2-phenyl substituent on the gauche-oriented methylene protons was revealed. © 1986 Plenum Publishing Corporation

Stereochemistry of seven-membered heterocycles. Communication 14. Synthesis and three-dimensional structure of 4-methyl-1,3-dioxa-5,6-benzocycloheptenes

1. On the basis of data obtained by the dipole moment method, cis-2-methyl (or phenyl)-4-methyl-1,3-dioxa-5,6-benzocycloheptenes have an equilibrium of chair and twist forms that is close in quantitative respects to the related 2-R-phthalyacetals; the spiroketal of cyclohexanone is realized in the e-Tw form; the methylal is conformationally inhomogeneous. 2. The isomeric 2-tert-butyl-4-methyl-1,3-dioxa-5,6-benzocycloheptenes, according to13C NMR data, are realized in chair conformations. An analysis has been made of the influence of the 4-methyl group on the chemical shifts of the carbon atoms of the seven-membered ring. © 1985 Plenum Publishing Corporation

Stereochemistry of seven-membered heterocycles. Communication 14. Synthesis and three-dimensional structure of 4-methyl-1,3-dioxa-5,6-benzocycloheptenes

1. On the basis of data obtained by the dipole moment method, cis-2-methyl (or phenyl)-4-methyl-1,3-dioxa-5,6-benzocycloheptenes have an equilibrium of chair and twist forms that is close in quantitative respects to the related 2-R-phthalyacetals; the spiroketal of cyclohexanone is realized in the e-Tw form; the methylal is conformationally inhomogeneous. 2. The isomeric 2-tert-butyl-4-methyl-1,3-dioxa-5,6-benzocycloheptenes, according to13C NMR data, are realized in chair conformations. An analysis has been made of the influence of the 4-methyl group on the chemical shifts of the carbon atoms of the seven-membered ring. © 1985 Plenum Publishing Corporation

Stereochemistry of seven-membered heterocycles. Communication 14. Synthesis and three-dimensional structure of 4-methyl-1,3-dioxa-5,6-benzocycloheptenes

1. On the basis of data obtained by the dipole moment method, cis-2-methyl (or phenyl)-4-methyl-1,3-dioxa-5,6-benzocycloheptenes have an equilibrium of chair and twist forms that is close in quantitative respects to the related 2-R-phthalyacetals; the spiroketal of cyclohexanone is realized in the e-Tw form; the methylal is conformationally inhomogeneous. 2. The isomeric 2-tert-butyl-4-methyl-1,3-dioxa-5,6-benzocycloheptenes, according to13C NMR data, are realized in chair conformations. An analysis has been made of the influence of the 4-methyl group on the chemical shifts of the carbon atoms of the seven-membered ring. © 1985 Plenum Publishing Corporation

Raman spectra and conformations of 2,2-dialkyl-1,3-dithio-5,6-benzocycloheptenes: coexistence of chair, boat and twist-boat forms

Raman spectroscopy has been applied to the title compounds; dithiaketals of acetone, methyl-ethylketone, ethylketone, pinacolone, cyclohexanone and fluorenone. A three-component chair⇋boat⇋twist-boat boat conformational equilibrium has been established for all compounds studied except the pinacolone derivative, which exhibits a two-component chair⇋boat equilibrium. Questions concerning the symmetry of the conformations based on depolarization data are discussed. © 1992

Raman spectra and conformations of 2,2-dialkyl-1,3-dithio-5,6-benzocycloheptenes: coexistence of chair, boat and twist-boat forms

Raman spectroscopy has been applied to the title compounds; dithiaketals of acetone, methyl-ethylketone, ethylketone, pinacolone, cyclohexanone and fluorenone. A three-component chair⇋boat⇋twist-boat boat conformational equilibrium has been established for all compounds studied except the pinacolone derivative, which exhibits a two-component chair⇋boat equilibrium. Questions concerning the symmetry of the conformations based on depolarization data are discussed. © 1992