1.4- Dioxane ring

In the case of the dihexulose dianhydrides containing three spino-linked rings, it is perhaps inappropriate to use the terms endo- and exo- without any fixed point of reference—especially because both effects have the same origin. An appreciation of the outcome of these electronic effects can be obtained by taking the 1,4-dioxane ring as the point of reference. This ring adopts a conformation... 

Fic. 2.—Conformations of the 1,4-dioxane ring with (a) differing and (b) the same anomeric configurations of the glycose residues... 

The chair conformation of the 1,4-dioxane ring is also preserved in the channel of the hexakis(/3-naphthylthio)benzene-l,4-dioxane host-guest complex (82TL4131). 

Heterocyclic polymers containing the 1,4-dioxane ring have been mentioned only briefly in the literature. Cationic addition polymerization of 1,4-dioxene (151) produces polymer (152 Scheme 48) which, along with other poly(l,2-dialkoxyethylenes), is reported to form polymeric complexes with poly(methacrylic acid) (79MI11109). 

A recent attempt to prepare the bis(ethylenedithio)tetrathiafulvalene derivatives fused with a 1,4-dioxane ring, viz. (89), by the Me Al-promoted reaction of organotin thiolate (87) with ester (88) was unsuccessful instead the reaction resulted110 in the production... 

Cationic polymerization of ethylene oxide exemplifies this behavior [91]. Due to the lack of strain of 6-membered 1,4-dioxane ring, this cyclic dimer of ethylene oxide is formed readily by back-biting. Its polymerization would involve AH — 0 and negative AS thus it is thermodynamically prohibited (equilibrium concentration of 1,4-dioxane is higher, than the highest attainable concentration, i.e., concentration in bulk). 

Ligands of type 1 have also led to interesting results in kinetic resolutions during Cu-catalyzed reactions of dialkyIzinc with cycloalkene oxides (eq. (1)) [18] and cyclohexenones [19]. On the other hand, monophosphonites bearing a fused 1,4-dioxane ring behave moderately in the Rh-catalyzed hydrosilylation of ketones (up to ca. 56 % ee) [20] cf. Section 2.6 Finally, a phosphapallada-cyclic complex has been reported as an exceptionally fast catalyst for the hydroarylation of norbomene (TONs up to 10 °) but with low ees (< 25 %) [21]. 

Specific acetalation can be performed on starch dialdehyde. Unlike starch, acetalated by aldehydes, the aldehydo groups on starch dialdehyde lead to the formation of acetals with alcohols. Acetals are formed randomly along the macrochain, moreover, 1,4-dioxane rings (25 and 26) also formed as a result of new, hemiacetal bonds.425,426 In such a manner, an allylated derivative was prepared with the use... 

N - N bond, was related to the high conformational strain of 109 [99]. No evidence of the configuration of the acetal carbons of the 1,4-dioxane ring was... 

The stereoselective synthesis of cyclohexanones containing both 1,3-dioxane and 1,4-dioxane rings was developed in order to provide novel tricyclic precursors of synthetic cyclitols (conduritols, quercitols, and inositols) (14SL1312). 

---