Conformational Analysis of oligo-1,3-Dioxan-4-yls

Abstract

Whereas simple 4,4Ј-bi(1,3-dioxanyl)s 16 and 19 displayed little conformational preference at the inter-ring bond, their derivatives 4 and 13, with equatorial methyl groups in the 5-and 5Ј-positions, each showed a strong conformational preference to populate a conformation with a gauche arrangement of the oxygen atoms. These results form the basis of a To relate material properties or biological functions of a flexible compound to structure Ϫ that is, to constitution Ϫ an understanding of the number and nature of low-energy conformations available to such a molecule is essential. In this context, we are interested in learning what modification of flexible alkane chains gives them the property that they populate predominantly one single conformation, or put another way, that they adopt a distinct shape despite maintaining flexibility. The key is to destabilize all the undesired backbone conformations related to the one desired conformation by suitable placement of substituents. A conceivable starting point for such an undertaking is represented by alkane chains bearing a single substituent at each of their secondary carbon atoms, such as 2,3,4,5-tetramethylhexane. We reported recently on the conformational analysis of meso-2,3,4,5-tetramethylhexane and of some of its derivatives. [2] The , isomer 1 should posess a distinctly different conformational behaviour. We elaborate here on how compounds with strong conformational preferences may be attained by structural modification of ,-2,3,4,5-tetramethylhexane.[ ‡] Flexible Molecules with Defined Shape, XIX. Part XVIII:Ref.[1] [a]

Proton affinity of proline and modified prolines using the kinetic method: role of the conformation investigated by ab initio calculations

“…Both the advantages and disadvantages of a linear synthesis can be illustrated in a synthesis of 96 ,48 which is related to 86 . As pointed out above, the stereochemical outcome of the synthesis of 86 was unpredictable and concrete proof of the relative configuration of the product was not available.…”

On the proposed structures and stereocontrolled synthesis of the cephalosporolides

“…PMB protection of alcohol 12 followed by Sharpless dihydroxylation afforded diol 14 [35–36]. DDQ oxidation of PMB ether produced 1,3-dioxane 15 [37].…”

Synthesis and Conformational Analysis of meso-Ter(1,3-dioxan-4-yls)

“…[1,2] This also holds for the inter-ring bonds in the ter(1,3-dioxan-4-yls) 3 and 4. [3] Our previous synthesis of 3 and 4 was rather ineffective and did not capitalise on the symmetry (meso) of these compounds. As we wanted to study the conformational preferences of additional (meso) symmetric ter-dioxanyls 2, a different synthetic approach to this class of meso compounds appeared necessary.…”

“…the values of 2.4 and 2.5 Hz for the previously described [3] compounds 3 and 4). We therefore conclude that the product is compound 10 and not 34.…”

“…Evidence that 10a is indeed the predominant conformer (as predicted by the force-field calculations) is provided by the determination of the indicated 3 J C,H coupling constant to 3.0 Hz, characteristic [36] of a CϪCϪCϪH gauche arrangement. The behaviour of compound 10 is thus in line with the analogues 3 and 4; [3] that is, with expectations and calculations.…”