Aziridines fluorination

Tnfluoromethyl hypofluonte will fluorinate Schiff bases, giving N,a,a-tn-fluoroatmnes and a-fluoroimines [144] and reacts with diazoketones to give adducts in modest yields [145] (equation 6) At-Substituted aziridines give nng opened products by 1,3 addition of fluonne on nitrogen and trifluoromethoxy on carbon [146] (equation 7)... 

Halides in heterocyclic compounds can also be reduced selectively by tin hydrides. For example, the more reactive chlorine in a fluorinated aziridine can be reduced readily using very mild conditions and without a catalyst75. Again, the more reactive chlorine is reduced preferentially (equation 67). 

Dichlorocarbene reacts exothermically under soliddiquid two-phase conditions with azides to produce, initially, isocyanide dichlorides, RN=CC12, which can react further to give A-alkyltetrachloroaziridines [50], The aziridines are the major products (60-70%) with simple alkyl azides, but the reaction tends to stop at the isocyanide step (50-60%), when the alkyl group is highly fluorinated. 

The formation of A-fluorinated aziridine-2-carboxylates can be achieved by fluori-nolysis of their IV-aminomethyl derivatives, apparently via the immonium ion-fluoride ion pair formed by initial electrophilic attack of F2 on nitrogen. ... 

G.M. Alvernhe, C.M. Ennakoua, S.M. Lacombe u. A. J. Laurent, J. Org. Chem. 46, 4938-4948 (1981) Ring Opening of Aziridines by Different Fluorinating Reagents Three Synthetic Routes to a,/J-Fluoro Amines with Different Stereochemical Pathways". 

Fluorinated triazolines (Scheme 29) are particularly stable and require high temperatures for thermolysis when aziridines are obtained.145 Thermolysis of aryl-substituted triazolines is not well investigated144,175 the l-p-nitrophenyl-5-phenyl compound yields exclusively aziridine, whereas the 1,4-isomer gives the imine as the major product.175 1-Heterocyclic-substituted 5-vinyltri-azolines (Scheme 31) give S-vinylaziridines, which undergo thermal isomerization to azepine derivatives (e.g., 89).183... 

Calculations at the MP2(Full)/6-31++G(d,p)//MP2(Full)/6-31+G(d) level of theory were used to investigate the SN reactions between ammonia and aziridine, aze-tidine, methylethylamine, and four fluorinated derivatives of aziridine.52 The results show that aziridine and azetidine have strain energies of 27.3 and 25.2 kcalmol-1, respectively, and that as a consequence they react 7.76 x 1023 and 2.30 x 1017 times faster with ammonia than does the methylene group of methylethylamine. However, even after subtracting the effect due to the release of ring strain, aziridine still reacts much faster than the other two substrates. This is because the electrostatic attraction of the charges in the product-like dipolar transition state are much greater for aziridine. 

Recent progress on the use of hypervalent iodine reagents for the construction of carbon-het-eroatom (N, O, P, S, Se, Te, X) bonds is reviewed. Reactions of aryl-A3-iodanes with organic substrates are considered first and are loosely organized by functional group, separate sections being devoted to carbon-azide and carbon-fluorine bond formation. Arylations and alkenyla-tions of nucleophilic species with diaryliodonium and alkenyl(aryl)iodonium salts, and a variety of transformations of alkynyl(aryl)iodonium salts with heteroatom nucleophiles are then detailed. Finally, the use of sulfonyliminoiodanes as aziridination and amidation reagents, and reactions of iodonium enolates formally derived from monoketones are summarized. 

Aziridine formadon from arylnitrenes, rather than via tiiazolines, is known for highly fluorinated arenes. Phenyl azide with trifluotoacetic acid generates a nitrenium ion which adds stereospecifically to alkenes to give aziridines. Yields are rather low, pardy due to concurrent ring opening of the aziridine by addidon of trifluoroacedc acid. Similar reacdons can be adiieved with Lewis acids such as AlCb. Enamines with aryl azides can yield either 2-aminoaziridines or amidines. ... 

As in other cases (vide supra), the stereochemical outcome in the case of bicyclic aziridines can be influenced by the choice of fluorinating agent and the reaction conditions. Thus, reaction of bicyclic aziridine 19 with hydrogen fluoride/pyridine yields c/.v-3-fluoro-2,3-diphenylazetidine (t7,s -20) after short reaction times. A longer reaction time, or the use of hydrogen fluoride alone, results in the thermodynamically more stable / r/ .9-isomer." ... 

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... 

An interesting use of the bond e disconnection for the synthesis of perfluoro aziridines was reported <1999CC47>. Treatment of perfluoro imine 65 with an excess of PhLi provides the aziridine 67 in good yield (Equation 20). This reaction is believed to go through intermediate 66 after an initial addition of 2 equiv of PhLi. A subsequent nucleophilic attach of the nitrogen anion to displace a fluorine results in aziridine ring formation. The ease with which this strained system forms is attributed to relief of the 1,3-diaxial interactions found in intermediate 66. In addition, an X-ray structure of aziridine 67 was obtained. 

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