Aziridination chalcones

The reaction of 2 -benzyloxychalcone dibromides (605) with ammonia gives a chalcone aziridine (606). Following conversion to the (V-benzoyl derivative, acid hydrolysis removed the protecting group at C-2 and a 3-aminoflavanone results (Scheme 230) (73ACH(76>95). 

The use of the bisoxazolinylanthracene ligand AnBOX in an Evans-like aziridination of chalcones has thrown up the interesting observation that the sense of enantiodiscrimination is inverted in relation to the reaction carried out with a traditional BOX ligand with similar stereogenicity (Scheme 4.17) [16]. 

The aziridines are the nitrogen analogs of the epoxides and undergo similar electrophilic reactions. No biological data were obtained for these compounds nor were they used as precursors to any CA-4, 7, analogs. They have been included since the synthesis is noteworthy, and they could be interesting intermediates. Xu et al. stereoselectively aziridinated chalcones using the nitrene precursor (PhINTS) and a copper catalyst to form compound 141 (Scheme 36) [82],... 

Phase-transfer catalytic conditions provide an extremely powerful alternative to the use of alkali metal hydrides for the synthesis of cyclopropanes via the reaction of dimethyloxosulphonium methylides with electron-deficient alkenes [e.g. 54-56] reaction rates are increased ca. 20-fold, while retaining high yields (86-95%). Dimethylphenacylsulphonium bromide reacts in an analogous manner with vinyl-sulphones [57] and with chalcones [58] and trimethylsulphonium iodide reacts with Schiff bases and hydrazones producing aziridines [59]. 

Highly substituted chalcones and one equivalent of NH2OH afforded substituted trans-2-benzoyl-3-phenyl-1H-aziridines . ... 

Keywords chalcone, benzylidene aniline, trimethyloxosulfonium iodide, ylide reaction, cyclopropane, aziridine... 

Aziridination of ( )-chalcones can be carried out with other aminoimines which are formed by deprotonation of A-amino-A-methyhnorpholinium salts [58]. 

Synthesis of annelated diazepines based on unsaturated aromatic diazepines may involve the preliminary transformation of ketones into the corresponding l,3-diaryl-2,3-dibromopropane-3-ones (chalcone dibromides). The interaction between o-PDA or some of its substituted analogues with chalcone dibromides leads to the formation of aziridine derivatives [64] (see Chap. 1). However, in the case of 4-nitro-o-PDA, either azirenoquinoxalynes 53 or benzodiazepine derivatives 54 may be obtained depending on the reaction conditions [65] (Scheme 4.15). Diazepine derivatives 56 are obtained by the condensation of chalcone dibromides 51 with 5,6-diamino-1,3-dimethyluracil 55 [66], but aziridine derivatives are not isolated in this reaction. It should be noted that compounds 54 and 56 are formed owing to cyclization of the intermediate (3-enaminoketones [65, 66, 67] and are easily isolated from the reaction mixture. 

In a different context, Troger s base 137 has been identified as a suitable catalyst for the enantioselective aziridination of chalcones using O-mesityle-nesulfonylhydroxylamine as the functionalized nucleophile undergoing the... 

Scheme 7.86 Enantioselective aziridination of chalcones catalyzed by Troger base.

Thiophen-2-aldehyde has been used in a preparatively useful modification of the Knoevenagel reaction in which TiCU and a tertiary amine in tetrahydrofuran were used in order to achieve facile condensation with ethyl acetoacetate and ethyl nitroacetate. The reaction of the dibromo-derivative (155) obtained from the corresponding chalcone with cyclo-hexylamine gave the 2-(2-thienyl)aziridine (156). The reaction of (156)... 

Reaction Conditions. Stir the reaction mixture for 15 min. Then wrap the flask with aluminum foil and continue to stir the system for 24 h.The reaction may be worked up at this point or stored in the dark for 1 week if necessary. Do not expect the chalcone to immediately dissolve in the reaction medium it will do so over the course of several hours as the aziridine product begins to precipitate. If you wish, you can occasionally magnetically stir the reaction mixture for 15-20 min during this intervening period. 

Copper complexes of bisoxazoline ligands [90] such as 76 with a more rigid structure and other optimized bisoxazoline ligands [91] can asymmetrically aziridinate chalcone substrates with high enantioselectivities. 

In 2010, chiral tridentate ligand 25, containing two stereogenic centres, one located on the sulfinyl sulfur atom and the other on the carbon atom in the aziridine moiety, was found by Lesniak and Kielbasinski to be a very efficient nickel ligand for the enantioselective conjugate addition of diethylzinc to chalcones as well as cyclohex-2-enone (Scheme 2.24). The... 

Scheme 2.24 Conjugate additions of diethylzinc to chalcones and cyclohex-2-enone with an in situ generated aziridine sulfoxide nickel catalyst and an in situ generated aziridine alcohol nickel catalyst.

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