Aziridines bicyclic ring systems

Similarly, in a 1,3-dipolar cycloaddition of DMAD to the conformationally locked cyclic a-alkoxycarbonylnitrone (727), bicyclic ring systems, containing a nitrogen atom at the bridgehead position have been synthesized. A mechanistic interpretation of the origin of the fused pyrroles (729) includes the intermediate formation of the aziridine ring in (728) (Scheme 2.303) (820). 

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. 

When the related aziridine 195 was used containing one less carbon in the tether, an unusual cyclization occurred which corresponds to a formal [3+2] aziridine allylsilane cycloaddition to give the bicyclic pyrrolidine 196. This substrate was used for the preparation of other fused ring systems (Scheme 53) <1999T8025>. 

When an aziridine ring is fused at the 2,3-bond to another ring system, the only ring opening structurally allowed is a disrotatory rotation, which must be photolytically performed as discussed above. Thus, the fused aziridine 8 on irradiation generates syn-azomethine ylide 9, which is captured by an acetylene to give a bicyclic cycloadduct (68CPB764). 

Rearrangement. The photochemical rearrangement of a variety of bicyclic aziridine ring systems has been studied by Padwa and co-workers. Photolysis of the diazabicyclo[3,l,0]hexene (586), obtained from photoinduced dimerization of the azirine (585), gave a mixture of cis- (587) and trans- (588)... 

The presence of the aziridine ring in bicyclic system 116 leads to nucleophilic attack at C(4), affording seven-membered heterocycles 117 (Equation 24) <20020L2481>. 

---