Aziridines A-halogenation

Darzens reactions between the chiral imine 52 and a-halo enolates 53 for the preparation of nonracemic aziridine-2-carboxylic esters 54 (Scheme 3.17) were studied by Fujisawa and co-workers [61], It is interesting to note that the lithium enolate afforded (2K,3S)-aziridirie (2i ,3S)-54 as the sole product, whereas the zinc enolate give rise to the isomer (2S,3i )-54. The a-halogen did not seem to affect the stereoselectivity. 

The strained ring in aziridines makes them reactive, with ring opening under attack from any nucleophile to create a new nucleophUe-carbon bond. Aziridine rings can be formed from intramolecular substitution of a halogen atom by the nitrogen in nitrogen mustards. 

A somewhat similar ring closure in which a nitrogen anion attacks a halogenated carbon center is obtained in the anodic oxidation of dimethyl Q -(it -tosylaminoalkyl) malonates in methanol containing KI in an undivided cell. Aziridines, azetidines, and pyrrolidines may be formed in good yield [63]. 

The 4-halogen atom in chloroquinazoline was displaced by aziridine, by amines (with derivatives of a-amino acids), and by fluorine (with KHF) more readily than a halogen atom at C-2. When a 4-fluorine atom was activated, as in hexafluoroquinazoline, it could be readily substituted by an amino or methoxy group. Nucleophilic substitution in the benzene ring of quinazoline was also possible. Hexachloroquinazoline gave hexafluoroquinazoline with anhydrous potassium fluoride, and the latter... 

The photoirradiation of 1-(2-naphthoy1)aziridine in halogenated hydrocarbon solvents gave a complex mixture of products amongst which... 

A wide variety of three-membered heterocyclic rings are formed by a 1,3-elimination of HX . Such reactions occur with particular facility when the heteroatom carries the hydrogen atom and X is a halogen or an ester function. Typical examples are the conversions of 2-halogenothiols, 2-halogenoalcohols and 2-halogenoamines into cyclic sulphides, epoxides and aziridines, respect-... 

Cancer chemothCTapeutic agents as a rule poorly penetrate the blood brain barrier. Brain tumors are thus not readily treatable by chemotherapy. Diaziquone (at one time known as AZQ) is an exception to this generalization. Treatment of chloranil (213) with the anion from urethane gives intermediate 214, probably by an addition elimination scheme. Displacement of the remaining halogen with aziridine yields diaziquone (215) [.55J. 

Neither aromatic halogens [232,602] nor nitro groups were affected during the reductions of the azido group [232, 247, 602]. a-Iodo azides gave, on reduction, aziridines or alkenes depending on the substituents and on the reagents used [603]. 

Suitable methods for linking a phosphorus—nitrogen bond to the aziridine ring are the aminolysis of halogenated phosphorus compounds (2,280—282), the transamination of phosphoramines with excess aziridine (283), the reaction with phosphites (284) and phosphoramidites (285) which have a free OH group, or the reaction of phosphines with aziridines and carbon tetrachloride (286). 

The nitrogen source for the aziridination of alkenes, a nitrene or nitrenoid, can be generated in various ways (1) oxidation of a primary amine (2) base-induced -elimination of HX from an amine or amide with an electronegative atom X (X = halogen, O) attached to the NH group or by -elimination of metal halides from metal A-arenesulfonyl-A-haloamides (3) metal-catalyzed reaction of [A-(alkane/arenesulfonyl)imino]aryliodanes (4) thermolytic or photolytic decomposition of organyl azides and (5) thermally induced cycloreversion reactions . 

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