Cyclic aziridine

Intramolecular alkylnitrene addition to an alkenic moiety situated S,e to the electron deficient center has been utilized for the preparation of bi- and tri-cyclic aziridines (Scheme 11) (68JA1650). Oxidation of the primary alkylamine can be effected cleanly with NCS, LTA or mercury(II) oxide. 

Nitriles can act as nitrogen nucleophiles in aziridine ring-opening reactions. Two examples are shown in Scheme 25 in which a formal [3-1-2] cycloadduct is the final product. Tosylaziridine 147 was reacted with benzoni-trile and BF3 OEt2 catalysis to produce the r-fused imidazoline 148 <2004TL1137>. The utility of the reaction is limited in the case of cyclic aziridines to benzofused aziridines and either aryl or benzyl nitriles. It was also found that the reaction required stoichiometric BF3. Lesser amounts of Lewis acid reduced the chemical yield drastically. 

Indirect electrooxidation of cyclic aziridines using NaCl or NaBr as a redox catalyst results in C(l)-C(2) bond cleavage under formation of the corresponding keto nitriles. This reaction is explained by the intermediate generation of an azaallenyl cation, which is hydrated to the o -hydroxyimine. Further oxidation by Cl" then would lead to the open-chain keto A-chloroimine, which by HCl elimination forms the keto nitrile, while its hydrolysis leads to the keto aldehyde as a side product [32] ... 

A domino organophosphine-catalyzed nucleophilic ring opening/cydization of cyclic and acyclic aziridines with carbon disulfide and isothiocyanates providing a simple and convenient route to thiazolidinones 91 (from CS2) has been reported by Hou and coworkers [37] (Scheme 4.18). Thus, the reaction of cyclic aziridine 55 from cyclohexene (n=l) with carbon disulfide in the presence of 10mol% of BU3P in t-butyl alcohol affords trans-l,3-thiazolidine 91a in 92% yield. On the other hand, no product was obtained from aziridine derived from cyclopentene (n = 0), whereas the reaction of aziridine from cycloheptene (n=2) afforded the corresponding thiazolidine 91c in 41% yield. Similarly, the acyclic aziridines 65... 

The reaction of the vinylcyclopropanedicarboxylate 301 with amines affords an allylic amine via the 7r-allylpalladium complex 302[50]. Similarly, three-membered ring A -tosyl-2-(l,3-butadienyl)aziridine (303) and the four-mem-bered ring azetidine 304 can be rearranged to the five- and six-membered ring unsaturated cyclic amines[183]. 

SULFURIZATIONAND SULFURCm ORINATION] (Vol23) -reaction with aziridine [IMINES, CYCLIC] (Vol 14)... 

Cyclic Carhene Complexes. The reaction of aziridines with carbonyl, thiocarbonyl, or isonitrile ligands in Mn, Re, Fe, Ru, Pd, or Pt complexes leads to formation of cycHc carhene complexes (324—331). 

Photoelectron spectroscopic studies show that the first ionization potential (lone pair electrons) for cyclic amines falls in the order aziridine (9.85 eV) > azetidine (9.04) > pyrrolidine (8.77) >piperidine (8.64), reflecting a decrease in lone pair 5-character in the series. This correlates well with the relative vapour phase basicities determined by ion cyclotron resonance, but not with basicity in aqueous solution, where azetidine (p/iTa 11.29) appears more basic than pyrrolidine (11.27) or piperidine (11.22). Clearly, solvation effects influence basicity (74JA288). 

In aqueous solution, azetidine (p/sTa 11.29) is slightly more basic than pyrrolidine and larger-ring cyclic amines and appreciably more basic than aziridine. It forms an addition compound (m.p. - 9 to -6 °C) with trimethylboron which is more stable than that formed by pyrrolidine (50JA2926, 64HC(l9-2)885). Azetidinium salts are well known (Section 5.09.2.2.7). 

Amino alcohols are also good substrates for aziridination under Mitsunobu conditions. The rfs-1,4-amino alcohols 48, obtained by reductive cleavage of the nitrogen-oxygen bonds of the hetero Diels-Alder adducts 47, underwent syn-SN2 -type displacement on treatment with PPh3 and DEAD to give cyclic vinylaziridines 49 (Scheme 2.15) [27]. 

The first of the nudeophilic ring-opening reactions of vinylaziridines discussed in this section is diborane reduction, developed by Laurent and coworkers in 1976 (Scheme 2.24). Treatment of N-unsubstituted vinylaziridines 89 with B2H6 gives allyl amines 92 by SN2 reduction via cyclic intermediates 90 [40]. In contrast, treatment with 9-BBN gives 2-(hydroxyethyl)aziridines 93 after oxidative workup (Scheme 2.25) [41]. 

Treatment of cyclic vinylaziridine 105 with organocuprates of the R2CuLi type proceeds in a highly syn-selective manner (Scheme 2.29) [46], The syn stereochemistry of the reaction reflects the effect of the acetonide group, which directs the nucleophilic attack to the less hindered a-face. The formation of SN2 products 109 from the cyclic (chlorovinyl)aziridine 107 can be explained by assuming a syn-SN2 ... 

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