Aziridines, reaction with Subject

Further, a comparison of the effects of ligand on enantioselectivity in the cyclo-propanation and aziridination reactions revealed a linear relationship. Jacobsen argues that this reinforces the mechanistic analogy between these group-transfer reactions and suggests that the transition states are subject to similar selectivity determining factors. Finally, Jacobsen observed ligand acceleration with the diimines in this reaction. 

In addition to alkenes, imines are tremendously popular aziridine precursors via an aza-Darzens approach. For example, a stereoselective synthesis of C-sulfonylated aziridines was reported via an aza-Darzens approach employing bromomethyl phenyl sulfbne, NaHMDS, and a series of N-tert-butanesulfinyl imines (14MI969). Likewise as shown below, chiral tert-butane- and mesitylsulfinimines were subjected to an aza-Darzens reaction with substituted 2-bromoesters to provide a host of aziridines in good yield with excellent stereocontrol (14OL6920). In turn, these aziridines could be subsequently converted to chiral A/-H aziridines in a total of three steps starting with a wide range of commercially available aldehydes. 

Reaction of the l-aryl-2-phenacylcyclopropanes with chlorosulphonyl isocyanate and subsequent removal of the chlorosulphonyl group with benzenethiol in pyridine affords the 4,5-dihydro-1,3-oxazepines (91) <95SCI939> and in a reaction sequence in which an aziridine is the source of nitrogen, methyl l-benzyloxycarbonylaziridine-2-carboxylate reacts with 2-(N-benzyl-A -/t /7-butoxycarbonyl)aminoethanol to give the derivative (92) which, after removal of the Boc group, is subject to a reductive cyclisation to yield the hexahydro-l,4-oxazepine (93) <95CPBI 137>. 

The reactions w crc performed under a Nj atmosphere. Anhyd HF (ca. lOmL) was introduced into a polyethylene flask, cooled in liquid air, and aziridine (0.02 mol) wa.s then added portionwisc with stirring. The mixture was brought to rt, stirred for 1 -12h, and then subjected to water-pump vacuum for 10 min to evaporate the remaining HF. The residue was treated cautiously with sat. aq NaHCOj (200mL) and... 

Other examples have been provided by the anodically initiated isomerization of several decarbene metal carbonyl couples [197]. Electrochemical induction of chemical reactions can also be successfully used for conversion of alcoolates into ketones with simultaneous reduction of aromatic halides [198], the tetramerization of aziridines [199], or ligand substitution [200] in organometallic compounds. A useful review on this subject was published [201]. 

Adridines. A synthesis of aziridine-2-carboxylic esters by the reaction of hexahydro-l,3,5-triazines with alkyl diazoacetates in the presence of SnCl is subject to asymmetric induction by a chiral substituent attached to the nitrogen atom. ... 

In this chapter, key studies which have led to the current understanding of the mechanism of this transformation will be discussed, as a basis for dealing with issues of selectivity and choice of experimental variables in subsequent sections. Since the initial development of this reaction, it has evolved in scope to become a primary method for the stereoselective synthesis of epoxides to which an electronegative substituent is directly attached. Several recent variations on the initial protocol which afford functionally diverse molecules are the subject of Section 1.13.3. Section 1.13.5 examines related reactions that afford substituted aziridines instead of epoxides, and Section 1.13.6 examines some recent variants of the re-... 

Two theoretical studies on the structure of aziridine have been published, one relating to the effect of hyperconjugation on the barriers to the inversion of nitrogen and the other to the structures of aziridine-enamines. The reaction by which (270 R = H, Me, or NH2) are hydrolysed to cis- and to trans- 27 ) has been subjected to ab initio calculations. Theoretical predictions have been found to agree with experimental results. 

The addition reaction between amines and carbon disulphide has attracted the attention of several research groups because it constitutes a common route to dithiocarbamates. In their latest paper, Fitton and his co-workers, by means of cross-over experiments and the application of optically labelled bases, have further established that the reaction of benzylic, tertiary amines with carbon disulphide proceeds by an inter-molecular addition-elimination-recombination mechanism. On the other hand, Kreutzkamp and his co-workers claim that the insertion reaction of carbon disulphide with tertiary Mannich bases proceeds by an intramolecular mechanism. The synthesis of thiazolidine-2-thiones by the insertion reaction of carbon disulphide with aziridines has been the subject of two recent papers. - One of these deals mainly with the mechanistic and stereochemical aspects of this reaction, which was studied using 2-substituted and cis- and rra/z5 -2,3-disubstituted aziridines as reactants. A mechanism accounting for the stereoselectivity of the reaction has been drawn up by the authors (Scheme 7). 

The products may be isolated by fractional distillation but, on occasion, separation of the mixtures presents formidable difficulties, even by gas chromatography, and the relative proportions of the products can only be computed indirectly after having been subjected to further reactions. Phenyl isopropyl ketone yields the thiazolidine almost exclusively (55%). The observed cyclizations may be accounted for by several mechanisms, but the experimental evidence does not as yet allow of a final choice. Under the usual conditions, ethyleneimines and aldehydes yield merely adducts, viz. l-(hydroxyalkyl)aziridines (286), which fail to react with... 

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