Bicyclic aziridine ring-opening

Recent Studies of Pyridinium Salt Photocyclization Bicyclic Aziridine Ring-Opening Processes... 

The intramolecular aziridination of alkoxycarbonyl azides derived from ( )-5-hydroxymethyl-2(5//)-furanone, via thermal decomposition to nitrenes, gave the tricyclic compound 34 which was successively converted to the bicyclic compound 35. The aziridine ring opening with hydrazoic acid/ sodium azide ion of the aziridines 34 and 35 gives azido lactones 36 with the xylo configuration mixtures of xylo- and (y.w-forms were obtained by partial epimerization in equilibrating conditions and were easily separated60. 

Fukuyama (2007) plan for oseltamivir phosphate tandem [2.2.1] bicyclic ring opening andaziridine ring formation in step 9 and aziridine ring opening in step 10. 

Okamura-Corey (2008) plan for oseltamivir phosphate [2.2.2] bicyclic ring opened by rednction (step 6) aziridine ring opening in step 12. 

The aminocyclopentene products of these pyridinium salt photoreactions were shown to arise by acid-catalyzed methanolytic aziridine ring opening of bicycHc aziridine intermediates. Accordingly, treatment of the bicyclic aziridines 24 and 25, produced by irradiation of basic MeOH solutions of the salts 20 and 21, with catalytic quantities of HCIO4 in MeOH led to smooth formation of the respective aminocydo-pentenes 22 and 23. Thus, when base is not included in pyridinium salt photoreaction mixtures, the initially formed photocyclization products are N-protonated bicycHc aziridines, which are subject to nucleophile-induced cleavage at their allylic aziridine centers. 

P-Lactams have been used as a synthon for the preparation of a vast array of compounds. It has been reported that the reduction of 4-(haloalkyl)azetidin-2-ones with LiAlhL is a powerful method for the synthesis of stereodefined aziridines and azetidines <06OL1101>. However, reduction of 4-(haloalkyl)azetidin-2-ones with chloroalane afforded 2-(haloalkyl)azetidines, which were rearranged to 3,4-cw-disubstituted pyrrolidines and piperidines 32 <060L1105>. During these rearrangements, bicyclic azetidinium intermediates were formed which were ring opened by halides. The synthesis of a peptide-... 

Thiazine 283 has been prepared through the nucleophilic ring opening of fused bicyclic aziridine isothiazoli-dine 1,1-dioxide 284 with MeOH in the presence of BF3-OEt2 (Equation 40) <20000L2327, 2004JOC6377>. 

A strategy for the synthesis of trehazolamine has been developed from 1-methox-yethoxymethyl-3-pivaloyloxymethylpyridinium perchlorate via amino cyclopentane derivatives (Schemes 42 and 43).115 Pyridinium salt 351 was prepared by a two-step sequence from 3-(hydrooxymethyl)pyridine 349 via 350 (Scheme 42). Irradiation of 351 in aqueous NaHC03 led to production of the separable bicyclic aziridines 352 (20%) and 353 (16%). Ring opening of 352 by acetic acid, followed by removal of the... 

Bicyclic aziridines 17 with a l-azabicyclo[n.l, 0]alkane framework can also be subjected to ring opening with either hydrogen fluoride or the hydrogen fluoride-pyridine complex to give 3-fluoro-l-azacycloalkanes 18. ° ° ... 

An important ring opening of bicyclic aziridines involves aziridines derived from carbohydrates (in their pyranoside or furanosidc form) which yields interesting fluorinated carbohydrate de-rivates.104-105 An example is the ring opening of aziridine 21 with tetrabutylammonium fluoride to give (benzoylamino)fluoropyranoside 22, an intermediate in the synthesis of protected C 2 analogs of daunosamine.104... 

The ring-opening reaction can also be induced by attack of oxygen-centered nucleophiles, as demonstrated by the facile ring cleavage of the unsymmetrical bicyclic aziridine 60 with methanol in the presence of boron trifluoride etherate to give the product of attack at the more-substituted aziridine carbon <2002T7355>. Indium triflate... 

Several thiazolidines were synthesized via titanium tetrachloride catalytic cyclization <2005JOC227>. The reaction proceeds via an intramolecular attack on the nitrile by the aziridine nitrogen to provide bicyclic aziridinium intermediate 91. Subsequent ring opening by chloride yields thiazolidine 92 (Scheme 25). 

Type I aziridines can be prepared via photolysis of functionalized pyridinium ions. Mariano and co-workers have shown that irradiation of pyridinium ion 40 via a 450 W Hanovia lamp with Vycor filter will induce a ring contraction to produce a fused-bicyclic aziridine moiety 41 (Equation 16) <1996JOC4439>. The azabicyclo[3.1.0]hexane prepared through this method can rapidly experience nucleophilic opening to produce an amine-substituted cyclo-pentene. 

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). 

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