Aziridines synthesis from oxiranes

A convenient new synthesis of aziridines (40) from oxirans and phosphazenes has... 

Chiral aziridines have become available starting from oxirane 34 with inversion at the chiral center, as illustrated with the synthesis of 147." As described below, these aziridines can be elaborated with preservation of stereochemistry to afford a wide variety of derivatives. 

Carbon-Oxygen Bond Formation. CAN is an efficient reagent for the conversion of epoxides into /3-nitrato alcohols. 1,2-cA-Diols can be prepared from alkenes by reaction with CAN/I2 followed by hydrolysis with KOH. Of particular interest is the high-yield synthesis of various a-hydroxy ketones and a-amino ketones from oxiranes and aziridines, respectively. The reactions are operated under mild conditions with the use of NBS and a catalytic amount of CAN as the reagents (eq 25). In another case, N-(silylmethyl)amides can be converted to A-(methoxymethyl)amides by CAN in methanol (eq 26). This chemistry has found application in the removal of electroauxiliaries from peptide substrates. Other CAN-mediated C-0 bondforming reactions include the oxidative rearrangement of aryl cyclobutanes and oxetanes, the conversion of allylic and tertiary benzylic alcohols into their corresponding ethers, and the alkoxylation of cephem sulfoxides at the position a to the ester moiety. 

The same group also disclosed the synthesis of epz-7-deoxypaneratistatin via an aza-Payne rearrangement (254) (Scheme 7). Analogues of narciclasine (68), pan-crastistatin, and 7-deoxypancratistatin have been synthesized using modifications of the reported procedures as well as new methodologies (e.g. addition of indoles to oxiranes and aziridines derived from cyclohexadiene diols) (255-258). 

This section covers the synthesis of aziridines, oxiranes, /J-lactams and oxetanes. Aziridines are fairly important moieties in bioactive molecules and thus new routes for their synthesis are constantly being developed. /1-Lactams are probably the most important heterocyclic compounds that contain a single nitrogen atom, due to their importance in penicillin and cephalosporin chemistry. Their synthesis and chemistry has received much attention and much of this work has been reviewed544. The oxygen-containing heterocycles are much less commonly synthesized from double-bonded functional groups. 

Herein an overview of the most relevant approaches for the synthesis of un-natiual heterocycles of biological and industrial potential from carbohydrates is presented the natiual heterocycles have been previously reviewed [6]. This review is hmited to heterocycles with one or more of their carbon skeletons derived from carbohydrate precursors—those formed by cycloaddition reactions are not included. Also, carbohydrates with strained ring systems, oxiranes, aziridines, and thiiranes have aheady been reviewed and are not included herein [20]. The synthetic approaches for the reviewed heterocycles are divided according to the size of the heterocychc rings and the number of hetero atoms in the ring. The bicyclic ring systems are included under the smaller ring of their skeleton. 

Stereoelective polymerization of a racemic monomer is a sterical control polymerization process in which one of the monomeric antipodes is preferentially polymerized. If the conversion is not complete, both polymer and recovered monomer are optically active. It is synonymous with asymmetric-selection polymerization the yield can be simply evaluated from the optical activity of unreacted monomer. This theoretically important method of synthesis concerns, for the moment, mainly the polymerization of racemic three-membered heterocycles (oxiranes, thiiranes and aziridines) and of a-amino-7V-carboxy acid-anhydrides (or Leuch s salts). 

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