Structure and conformation of heterocycles. Part VI. The cis-1,4,5,8-tetraoxadecalin (hexahydro-p-dioxino[2,3-b]-p-dioxin) system: a chemical, conformational, and crystallographic study

Abstract

The title system (1)(a, b, c: R = H, CH2Br, or Me respectively) is subject of a multilateral investigation. cis-9,10-Bisbromomethyl-1,4,5,8-tetraoxadecalin (4a,8a-bisbromomethylhexahydro-p-dioxino[2,3-b]-p-dioxin)(1b) was obtained along with its bi(dioxolan-2-yl) isomer (2b) from the acid-catalysed condensation of 1,4-dibromo-butane-2,3-dione with ethylene glycol. Chemical correlation between derivatives in both series, viz.(1b → 1c) and (2b)→(2c), was achieved. Dynamic conformational analysis in solution was performed in a variable-temperature n.m.r. study of the octadeuteriated derivative, [2H8]-(1b), which was found to exist in solution as an inverting system with ΔG‡226 11·2 kcal mol–1, ΔH‡ 9·0 ± 0·9 kcal mol–1 and ΔS‡– 9 ± 4 e.u.