Ring opening of aziridines

Azomethine ylides are also frequently obtained by ring opening of aziridines, and the analogous carbonyl ylides from oxiranes. These aspects are dealt with in Section 3.03.5.1. A variety of five-membered heterocycles can also function as masked 1,3-dipoles and this aspect is considered in Section 3.03.5.2. 

Ring-opening of aziridine-2-carboxylates with alcohols has been reported to give (3-alkoxy-a-amino esters [16, 102]. Treatment of as-aziridine 127 (Scheme 3.45) with alcohol in the presence of a catalytic amount of boron trifluoride etherate afforded P-alkoxy-ot-amino esters 128 in 57-100% yields [16,102a], The reaction is both regio- and stereoselective, affording 128 as the only product. 

Carboxylic acids have also been investigated as nucleophiles in the ring-opening of aziridine-2-carboxylates [103]. Solvation of compounds 129 (Scheme 3.46) in acetic acid, for example, gave 130a and 130b in 83% and 89% yields, respectively. 

One of the key steps in the synthesis of actinomycin D (241 Scheme 3.88) and its serine analogue involved the regio- and stereoselective ring-opening of aziridine 238 with the acid 239 [138, 139]. This transformation took place in methylene... 

The ring-opening reactions of aziridines 16 with amines deserve special attention. Unlike ring-openings with the other nucleophiles examined, they do not require added base, and they do not produce stoichiometric byproducts (as with azide). In certain cases, they do not even require a solvent, as exemplified by the ring-opening of aziridine 18 (Table 12.12, entries 1-3). In addition, the reactions... 

Table 12.12 Nucleophilic ring-opening of aziridine 18 with amines.

The ring opening of aziridines takes place easily because of the great strain in the three-membered ring. Pt, Pd, Rh, and Ni are used as catalysts. Usually the sterically less hindered C-N bond is ruptured (Scheme 4.112). 

Thioacetals eliminate to vinylsulfides in the presence of CuOTf (Scheme 46).192 Cu1 and Cu11 triflates are mild Lewis acids for Friedel-Crafts acylation and alkylation reactions. CuOTf effectively catalyzes the reaction of anisole with selenoesters.193,194 Copper(II) sulfate promotes epoxide ring opening reactions in the presence of pyridine,195 with retention of configuration being observed. Cu(OTf)2 is a catalyst for the ring opening of aziridine by aniline.196... 

Synthetic work commenced with evaluation of an azomethine ylide dipole for the proposed intramolecular dipolar cycloaddition. A number of methods exist for the preparation of azomethine ylides, including, inter alia, transformations based on fluoride-mediated desilylation of a-silyliminium species, electrocyclic ring opening of aziridines, and tautomerization of a-amino acid ester imines [37]. In particular, the fluoride-mediated desilylation of a-silyliminium species, first reported by Vedejs in 1979 [38], is among the most widely used methods for the generation of non-stabilized azomethine ylides (Scheme 1.6). 

Triazole derivatives also result from the cycloaddition of DEAZD to azomethine ylids derived from electrocyclic ring opening of aziridines.117 121 For example, the tetrahydro-1,2,4-triazole 73 was prepared by thermolysis of the cts-aziridine in the presence of DEAZD in 96% yield (Eq. 8), and... 

Additionally, Wu and co-workers have shown regioselective ring-opening of aziridines with acid anhydrides mediated by imidiazolinylidene 3 [157]. This pathway requires the use of an electron withdrawing tosylated aziridine 310 in order for the reaction to proceed. The mild reaction conditions allow for a variety of products to be formed in high yields (Table 25). 

Scheme 46 Ring opening of aziridines catalyzed by NHCs...

Table 25 NHC catalyzed acid anhydride ring opening of aziridines...

P8 Thermal conrotatory 4tt ring opening of aziridines and epoxides is a well-recognized method of generating azomethine and carbonyl ylidesd (From Johnson, 2003)... 

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". 

Substitutions at saturated carbon atoms that are subject to control by remote functionalities may be best illustrated by the ring opening of aziridines [35] and epoxides [36, 37]. 

Fluoroethylamines 2 via Ring Opening of Aziridines 1 General Procedure 59... 

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