Planar chirality nomenclature

The R and S nomenclature has also been extended to the chiral plane (see for example [44]). Thus, structure XXXV has the (S) absolute configuration. Some confusion between chiral axes and chiral planes has led to the proposal of a new definition of the chiral plane and of a new procedure for specifying planar chirality [45]. 

The R and S nomenclature system can also be used for structures with an axis or plane of chirality if we apply the additional rule that substituents on the end of an axis or on the surface of a plane nearer the observer are arbitrarily given higher priority than those further away. Some authors augment the R and S labels in order to specify that the designation applies to axial or planar chirality, so the terms Ra and Sa (or aR and aS) for axial chirality and Rp and Sp (or pjR and pS) for planar chirality also appear in the literature. ... 

The basic problem of this suggestion was that the chirality descriptors obtained by the central procedure are the opposite of those derived from the planar approach. Schlogl consequently changed his stereochemical nomenclature [5,9] and. 

A first attempt towards an asymmetric synthesis by the lithiation reaction used (— )-spartein as a chiral additive [12,13], but the enantioselectivity was disappointing. With the chiral (S)-M-ferrocenylmethyl-2-methylpiperidine, a high diastereoselec-tivity was observed [12, 13, 112] (note that the polemic about the structure of the product is due to different stereochemical nomenclature, i.e., central vs. planar , as discussed in Sect. 4.1). A breakthrough was achieved by the readily resolvable... 

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