The stereochemistry of heterocycles

Comparative conformational analysis of 1,3-dioxane and 1,3-dithiane

“…They are separated by several potential barriers. It was established by molecular dynamics method that the fl exible conformers at heating and keeping at 295-300 K transformed into each other and in the chair conformer.The interest to the structural investigation of 1,3-dioxanes and 1,3-dithianes originates from the features of their structure, their application in the industrial and fi ne organic synthesis, and also their promising physiologically active properties [1][2][3][4][5][6][7][8][9]. In particular the great possibilities should be mentioned of the industrial application of cyclic acetals in the production of isoprene, 1,3-diols, and a number of drugs [1], and also in the synthesis of other six-membered 1,3,2-heterocyclic compounds [8], aminoalcohols and their derivatives [9].…”

Conformational analysis of 5-methyl- and 2,2,5-trimethyl-1,3-dithianes

“…Based on the experimental ( 1 H NMR) and theoretical vicinal coupling constants the ΔG 0 values were determined of the methyl group at the ring C 5 atom. The reasons for the distinctions between the values of this parameter from the ΔG 0 , obtained by energy minimizations of the equatorial and axial chair conformers are discussed.The interest in substituted 1,3-dithianes are due both to the peculiarities of their structure [1][2][3][4][5][6][7][8][9][10][11] and to their use as reagents in fine organic synthesis [12][13][14][15][16][17][18][19]. Earlier using 1 H and 13 C NMR spectroscopy it has been shown that the main minimum on the potential energy surface (PES) of 5-alkyl-1,3-dithianes is the equatorial chair conformer (C e ) [2, 3, 5-9].…”