Considerations about the chirality of the saturated six-membered rings with two or more heteroatoms

Abstract

The chirality of the title heterocycles is discussed considering their genesis by desymmetrization of the corresponding adamantanes. Some rules for the specification of the absolute configurations of the enantiomers (R or S) for this type of compounds are proposed. © 1996 Wiley‐Liss, Inc.

Synthesis and stereochemistry of new spiro[5.5]undecane derivatives with 1,3-dioxane, 1,3-dithiane, or 1,3-oxathiane rings

“…Reflux of 1,3-dioxane derivative with HCl in THF leads to deprotection of the mercapto group followed by transthioacetalization (procedure similar to the synthesis of 3, Scheme 4) and the obtaining of dithianes 9 and 10, respectively. In the next step, the 1,3-dithiane compounds (9 and 10) were Chart 1 Spirane skeletons with 1,3-dioxane (VII, IX), 1,3-dithiane (VIII, IX), and 1,3-oxathiane (X) rings Scheme 1 Conformational equilibrium for spiro [5.5]undecane submitted to the acetalization reaction with the formation of 1,3-dioxane-1,3-dithiane compounds (11,12), respectively. Formation of the corresponding bis(1,3-oxathiane) derivatives (XII) was not observed in this reaction; compounds 11 and 12 were purified by column chromatography.…”

“…The heterocycle is chiral and its flipping is an enantiomeric inversion (V ¡ VI) [11][12][13]. The chirality of the heterocycle can be attributed to a virtual tricoordinated chiral center (C*, Scheme 3, structures V and VI).…”

Six-Membered Ring Spiranes: Carbocycles and Heterocycles with Oxygen

“…The two monospirane units have the role of the two similar chiral centres and ring B exhibits a virtual tricoordinated pseudochiral centre. In previous works [28,29], we have demonstrated, using the desymetrization of adamantane, that saturated six-membered rings with different 1, 3 and 5 positions (e.g. 1,3-oxathiane ring) exhibit a virtual tricoordinated chiral centre (Scheme (4)).…”

“…Several synthetic approaches (Scheme (28)) to the cis and trans isomers of 1,7,9-trioxadispiro[5.1.5.3]hexadecane have been described [83,99,100].…”

“…Conformational studies on 1,7,9-trioxadispiro[5.1.5.3] hexadecane skeleton (76) were aimed at understanding the stereochemical course of thermodynamic spirocyclization from the acyclic diketodiol precursor (Scheme (28)) and, consequently, the steric and electronic effects that influence Scheme (25). the geometry of the ground state on these spiroketals.…”