Stereochirotopogenesis

In turn, stereochirotopogenesis is either nonrotative (Class 7A) or rotative (Class 7B). Each of the latter two subclasses can be stereoaselective, nonstereoselective or stereoselective vide supra). Nonrotative and rotative stereochirotopogeneses may be of the sp or sp variety. In Figures 18.16-18.19 (pp. 123,125-127), we provide examples of all the above subclasses. 

Figure 18.18 portrays examples of nonrotative stereochirotopogenesis (Class 7A). Transformations 96 and 97 represent two cases of the sp type- The first one of these transformations is nonstereoselective (483=486 and 484=485 constitute a racemate), while the second one can be either nonstereoselective-and-stereoselective (if racemate 489/490 and diastereomeric racemate 491/492 are formed in unequal amounts), or, doubly nonstereoselective (if racemate 489/490 and diastereomeric racemate 491/492 are formed in equal amounts). The remaining five cases (transformations 98-102) are sp nonrotative stereochirotopogeneses. Among these examples, 98 is stereoaselective (495=496=497=498), 99 is nonstereoselective (502/504 is a racemate which is astereomeric with respect to 501=503), whereas 100 and 101 are stereoselective (if diastereomers 507=508 and 509=510 are formed in unequal amounts if [507+508] = [509+510], the transformation would be nonstereoselective). Transformation 102 is stereoselective-and-nonstereoselective (if diastereomeric racemates 519 / 520 and 521/522 are formed in unequal amounts), or doubly nonstereoselective (if diastereomeric racemates 519/520 and 521/522 are formed in accidentally equal amounts). 

Finally, Figure 18.19 shows three cases of sp rotative stereochirotopogenesis (transformations 103-105), and six cases of sp rotative stereochirotopogenesis (transformations 106-111). Of the sp variety, 103 and 104 are stereoselective (or accidentally nonstereoselective). In transformation 103, stereoselectivity prevails if [525(=528)] [526(=527)] it does not, if the diastereomers in question are formed in equal amounts. Transformation 104 is stereoselective, if diastereomers 531(=534) and 532(=533) are formed in imequal amounts, or nonstereoselective, if the diastereomers are formed in equal amounts. Transformation 105 can be doubly stereoselective (the product mixture consists of imequal amoimts of the four diastereomeric products 537,538,539,540) or stereoselective-and-nonstereoselective (if two of the four diastereomers are formed in accidentally equal amoimts), or, doubly nonstereoselective (if, fortuitously, all four diastereomers are formed in equal amounts). 

Nonrotative astereochirotopogenesis (Class 6A) and stereochirotopogenesis (Class 7A) are expected with achiral reagents rotative modes (Classes 6B and 7B) are possible with chiral reagents. 

The first one of these transformations (118) yields a single chiral product, and is described as a noiurotative nonchirotopomutation - one that is avectoaselective and enantiofacioaselective. Transformation 119, in contrast, yields a racemate it is a case of nonrotative stereochirotopogenesis - nonvectoselective and enantiofaciononselective. 

Turning to Figure 18.27, we note that transformation 150 is a rotative stereochirotopogenesis that is diastereovectoselective and enantiofacioselective - resulting in the formation of four chiral diastereomers, 839-842. This process would have been considered, in the older terminology, a case of double diastereoselective synthesis. Finally, each of transformations 151 and 152 yields two astereomeric sets of diastereomeric pairs, 845,846,847,848 and 851,852, 853,854, respectively. Both transformations are rotative stereochirotopogeneses, with attendant astereovectoselectivity and enantiofacioselectivity. 

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