Conformational analysis. XVI. 1,3-Dioxanes

Abstract

A series of conformationally biased 2-, 4-, and 5-alkyl-l,3-dioxanes has been studied through acid-catalyzed equilibration of diastereoisomers and by nuclear magnetic resonance spectroscopy. The preferences of the alkyl substituents for the equatorial (over the axial) position are substantially different from corresponding preferences in cyclohexane and depend on the location in the dioxane ring. Quantitatively, these preferences (in kilocalories/mole) are Me-2, ^3.55; 2.9; 0.8; 0.7; 1.0; 1.0; 1.4. The data are rationalized in terms of the shape of the 1,3-dioxane ring and the "size" of the free electron pair on oxygen.

Conformational Studies of Substituted Trimethylene Sulfites by Proton Magnetic Resonance

“…Although compound 11 has been assumed to be a mixture of chair conformers (23,24) because of its dipole moment variation with solvent, alternative explanations involving non-chair forms seem more attractive. The single small coupling (5.3 Hz) points either to a mixture of non-chair forms (12,22,25) with near equal couplings but different dipole moments or to a mixture of chair and non-chair forms (which should have different dipole moments) (1 I), including the chair with an axial t-butyl group. We tend to favor the latter possibility as does Bentrude for the corresponding trans-5-t-butyl phosphite.…”

Structure, conformation, and mechanism in the membrane transport of alkali metal ions by ionophoric antibiotics

“…We studied the solution conformation of the sodium potassium and rubidium salts of monensin in chloroform solution using 1 H NMR spectroscopy at 500 MHz. 21 First, the spectra were solved using 1D and 2D methods.…”

Regioselective and stereoselective cleavage of cis‐4‐methyl‐2‐vinyl‐l,3‐dioxane by alkyllithiums

“…1 g) was added, and the mixture was stirred for 1 h before filtration to remove the solids. The filtrate was washed with 5 mL of diethyl ether, concentrated at reduced pressure, and distilled to give 12.8 g (40%) of the known dioxane: 6 Reaction of cis-4-Methyl-2-vinyl-1,3-dioxane (3) with n-BuLi A solution of 1.03 g (8.04 mmol) of cis-4-methyl-2-vinyl-1,3-dioxane (3) in 27 mL of dry n-pentane was cooled to )78°C and 3.90 mL (12.0 mmol) of a 3.08 M solution of nBuLi in pentane was added dropwise under an atmosphere of argon. The cooling bath was then removed and the reaction mixture was allowed to warm and stand at room temperature for 1 h prior to the addition of 10 mL of water.…”