Three-Membered Heterocyclic Rings, Illogical Electrophiles

The intramolecular nucleophilic substitution corresponds to disconnection (a) in the synthetic direction. In addition, the heteroatom as a nucleophile can act as a carbanion, resulting in cyclopropanation. 

The above scheme presents disconnections of oxiranes (epoxides), aziridines and thiiranes (thioepoxides) leading to six-electron synthons and their synthetic equivalents. 

CHBr3orCHl3/NaOH RCHsN2/metal cation reactivity of caibenes depends on the electronic properties of R 

R2NS-SNR2. MeaSiS-SSiMea elemental S + catalyst  

The following examples illustrate the practicability of syntheses of tricycles with reagents based on illogical synthons. First we discuss the epoxidation of the C=C bond in its achiral and chiral variant. 

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We already saw the term Umpolung for the inversion of natural polarity to obtain electrophiles in Sect. 4.2. In Sect. 5.2.2, we consider three-membered heterocyclic rings as a synthetically particularly interesting group of illogical electrophiles. 

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