Chiroptical properties

The stereogenic sulfur atom in sulfoxides is usually configurationally stable at room temperature thus, sulfoxides may be chiral based on this property alone1. In fact, there are many examples of optically active sulfoxides of both synthetic and natural origin. This chapter reviews the important methods for obtaining optically active sulfoxides, and discusses some reactions at sulfur which either leave the coordination number at three or increase it to four, generally with preservation of optical activity. It also describes briefly some recent studies on the conformational analysis and chiroptical properties of sulfoxides. 

Chiroptical Properties of Dendrimers with Chiral End Groups. .. 91... 

McGrath et al. have also thoroughly studied the chiroptical properties of dendrimers such as 40. They compared the optical activities of the series of 1st-, 2nd- and 3rd-generation compounds of type 40, considering the molar rotation per chiral unit ([ ]D/n) [75]. A big difference of the values was found between the generations which could possibly indicate chiral conformations inside the dendrimers, that enhance the optical rotation values per unit when... 

On the other hand, optically active telluroxides have not been isolated until recently, although it has been surmised that they are key intermediates in asymmetric synthesis.3,4 In 1997, optically active telluroxides 3, stabilized by bulky substituents toward racemization, were isolated for the first time by liquid chromatography on optically active columns.13,14 The stereochemistry was determined by comparing their chiroptical properties with those of chiral selenoxides with known absolute configurations. The stability of the chiral telluroxides toward racemization was found to be lower than that of the corresponding selenoxides, and the racemization mechanism that involved formation of the achiral hydrate by reaction of water was also clarified. Telluroxides 4 and 5, which were thermodynamically stabilized by nitrogen-tellurium interactions, were also optically resolved and their absolute configurations and stability were studied (Scheme 2).12,14... 

On the other hand, telluronium imides 13 were isolated for the first time in 2002 by optical resolution of their racemic samples on an optically active column by medium-pressure column chromatography.27 The relationship between the absolute configurations and the chiroptical properties was clarified on the basis of their specific rotations and circular dichroism spectra. The racemization mechanism of the optically active telluronium imides, which involved the formation of corresponding telluroxides by hydrolysis of the telluronium imides, was proposed (Scheme 6). 

A distorted conjugated pair of double bonds is an intrinsically chiral chromophoric system, and its overall chiroptical properties depend on the reduced symmetry of the chromophore itself as well as on the perturbing action of a dissymmetric environment. 

The problem of interpreting the chiroptical properties of highly distorted dienes remains, however, a different question (see Section II.D.3 below). 

The first report of the chiroptical properties of a planar s-fraws-diene chromophore is due to Di Corato12, who described the CD data of (+)-(S)-6, which shows a positive weak (Ae +0.2) Cotton effect at about 220 nm, in both the E and Z isomers. Lardicci and coworkers13 described in 1978 the absorption and CD spectra of the planar s-fraws-diene derivatives 7 and 41. 

An interesting series of s-trans planar dienes is that due to Walborsky and co-workers44,45. They prepared and studied the chiroptical properties of several compounds where the diene moiety is linked to a chirally substituted ring, such as 42 and 43. 

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