A-Acylaziridines

Because of the easy conversion of A-acylaziridines[471 into oxazolines, this method is also useful for protecting carboxylic acids furthermore, it is a means for resolving chiral carboxylic acids. 

In the asymmetric synthesis of the optically active a-acylaziridines 260 described recently by Furukawa et al. (293), the optically active o-methoxyphenylphenylsulfimide 157, which plays the role of the optical activity inducing agent, is converted to the corresponding sulfide. In this reaction, which involves a typical Michael addition of 157 to the carbon-carbon double bond followed by elimination of sulfide, the optical purities of the chromatographically purified... 

A-Acylaziridines 199 undergo nucleophile-induced (typically by an iodide)... 

A -acylaziridines substituted with an electron-withdrawing group produce a 2,4-disubstituted oxazoline as the major product. Borontrifluoride etherate (BF3 OEt2) has also been used successfully for an Al-benzoyl, but not an N-acetyl-substituted aziridine (Scheme 8.58). ... 

Miscellaneous Applications. PEIs and their derivatives are used as cementation auxiliaries in cmde oil exploration (459), and for breaking cmde oil emulsions (460) in cmde oil extraction. Seed coatings of water-soluble copolymers containing polyethyleneimine have been developed (461). Polyethyleneimine derivatives have positive photoresist properties (462) amidated polyethyleneimines improve the flow properties of cement (463) and with few exceptions, A/-acylaziridines act as chemical sterilizers for insects (464). 

This method has been exploited for the functionalization of [60]fullerene by using several aroyl azides166 and [2.4,6-tri-(tm-butyl)phenyl]oxycarbonyl azide16, which afforded the corresponding A -acylaziridines and subsequently the dihydrooxazoles, whereas azafulleroids were produced with [2-(trimethylsilyl)ethoxy]methyl azide and several benzylic azides presumably through the thermal decomposition of the intermediate dihydrotriazoles77. 

Details of the regioselective preparation of a variety of new 2,4-disubstituted oxazoles, using both iodide- and aeid-promoted rearrangements of A -acylaziridines, have been presented. It has been shown that two plausible mechanisms (S i and/or two S- 2 reactions) can account for the acid-catalysed transformation of 1-acylaziridines (447) to oxazolines (448), while the regioselective rearrangement of... 

A -acylaziridine-2-imides to oxazoline-4-imides, followed by hydrolysis of these latter compounds, has been used to afford chiral /1-hydroxy-a-amino acid precursors. It has been suggested that the observed thermal rearrangement of cw-aziridinyl ketone tosylhydrazones (449) to 5-alkylamino-3,5-diphenyl-l-tosyl-2-pyrazolmes (450) is... 

A-Acylaziridines can be deprotonated to yield enolates, which can participate in alkylations and aldol condensations <91TL2533, 94AG(E)599>. The aziridine ring was used as a chiral auxiliary, and good to excellent diastereoselectivity was obtained. Equation (47) shows an example of such an enolate alkylation. Quenching the enolate with an aldehyde produced a single syn aldol adduct. 

The use of C2-symmetric aziridines as chiral auxiliaries has been reviewed by Tanner <94AG(E)599>. Chiral A-acylaziridines such as (143) have been used in enolate chemistry (see Section 1.01.8.2). Aziridine-containing ligands such as (144) have been used for a variety of metal-catalyzed reactions such as the asymmetric dihydroxylation of alkenes, the palladium-catalyzed allylation of nucleophiles, asymmetric cyclopropanation, and aziridination <94AG(E)599,94TL4631). 

Aminolysis of mei o-epoxides is facilitated by Sc(OTf)3. In the presence of bipyridyldiol 8 chiral products are obtained/ mei o-A-Acylaziridines react with Me3SiN3 to provide (3-azido amines, and a chiral Bronsted acid (e.g., 9) renders the ring opening asymmetrical/ ... 

In addition to the classical form of the Michaelis-Arbuzov reaction, several non-classical variations have proved to be of great use with regard to general applicability and for the preparation of specific compounds. For instance, the ring opening of A-acylaziridines, by either trialkyl phosphites or phosphonous diesters, or by tris(trimethylsilyl)phos-phite, leads to dialkyl [2-(A-alkylamino)ethyl]phosphonates, or their bis(trimethylsilyl) diesters in A-protected forms from which A-protection may be removed under aqueous acid conditions (Scheme 13). 

Openings of mcso-epoxides to obtain chiral P-hydroxy nitrile derivatives and of A -acylaziridines to afford A-(P-sulfenylalkyl) amides have enlisted the service of ligand 23 and dicyclohexyl L-(+)-tartrate, respectively. An efficient method for acquiring chiral azido silyl ethers from epoxides and Me SiN, employs a (salenlCr-N, complex 24. "... 

Application to chiral A-acylaziridine-2-carboxylate gives the corresponding chiral 2-imidazolidine with the retention of configuration [40] (Scheme 3.24). This implies that the... 

Rearrangement of A -acylaziridines followed by oxidation is a well-known method of preparing oxazoles. There are several factors that control the regio-chemistry of the rearrangement in unsymmetrical aziridines. In the context of their approach to hahchondramides, Eastwood and co-workers studied this rearrangement and followed it with Ni02 oxidation to produce 2,4-disubstituted oxazoles. 

Bianthryl derivatives. The desymmetrization of A-acylaziridines (232) with MejSiSPh, catalyzed by commercially available (R)- and (S)-phosphoric acids (234), produced /i-(7V-acylamino)phenylthioethers (233) in a highly enantioselective and efficient manner (78-99% ee) (Scheme 64). ... 

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