Oxaziridine reactions with amines

Oxaziridines are powerful oxidizing agents. Free halogen is formed from hydrobromic acid (B-67MI50800). Reduction by iodide in acidic media generally yields a carbonyl compound, an amine and two equivalents of iodine from an oxaziridine (1). With 2-alkyl-, 2-acyl and with N-unsubstituted oxaziridines the reaction proceeds practically quantitatively and has been used in characterization. Owing to fast competing reactions, iodide reduction of 2-aryloxaziridines does not proceed quantitatively but may serve as a hint to their presence. 

It was reported only recently that A-methyl transfer from an oxaziridine to an amine occurs with formation of an N—N bond (79JA6671). N—N bond forming reactions with A-unsubstituted oxaziridines had been found immediately after discovery of this class of compound (64CB2521) and have led to simple hydrazine syntheses (79AHC(24)63). Secondary amines like diethylamine or morpholine are A-aminated by (52) in the course of some minutes at room temperature with yields exceeding 90% (77JPR195). Further examples are the amination of aniline to phenylhydrazine, and of the Schiff base (96) to the diaziridine (97). 

The permanganate ion oxidation of imines to nitrones is very much dependent on the reaction conditions. For the investigation of this dependency, reactions with benzylidene-r-butylamine, la, were carried out (equation 8). la was oxidized with m-chloroperbenzoic acid to give the corresponding oxaziridine 3a. As byproduct traces (<3%) of the nitrone 2a, amine 4a and benzaldehyde were formed. The permanganate ion and m-chloroperbenzoic acid may then oxidize the imine in two different ways. 

Acyloxaziridines are easily obtained from compounds unsubstituted at nitrogen by reaction with acid chlorides or isocyanates. Acylation proceeds so smoothly that, in the amination of carbonyl compounds, oxaziridine compounds are obtained in better yields on addition of acid chlorides than in the absence of the acylating agent. With aliphatic aldehydes, amination does not succeed at all except in the presence of benzoyl chloride. Proof of structure comes from reduction by iodide to give the acid amide and carbonyl compound. 

Irradiation of the diazepine N-oxide 8 gives a mixture of the 1,2-dihydroquinoxaline (10) and the oxadiazocine 11 through an intermediate oxaziridine (9). The dihydroquinoxaline undergoes acid hydrolysis to the quinoxalinone 12. It was subsequently shown that quinoxalinones of type 12 undergo ready reaction with ammonia or primary or secondary amines, in the presence of titanium tetrachloride, to give 3-amino- or... 

Starting with (5)-1 -phenylethyl amine, a chiral sulfonyloxaziridine has been prepared by A,T-sul-fonylation and subsequent formation of an imine with an aromatic aldehyde (best example pentafluorobenzaldehyde). Oxidation leads to a 1 1 mixture of diastereomeric oxaziridines 77 which can be separated by HPLC76. The compounds behave similarly to the chiral camphor-derived sulfonyloxaziridines, as they are able to epoxidize alkenes not containing special functional groups with some enantioselectivity (Section D.4.5.2.1.). Another attractive starting material is cheap commercial saccharin. Reaction with alkyl- or aryllithium compounds leads to addition... 

Oxaziridines are attacked by nucleophiles mainly at the nitrogen atom. The reactions of amines and sulphides with (370) proceed exclusively via attack at nitrogen by a concerted 5N2-type process, as shown in Scheme 19 thus PhSH and Me2NH react with (370) to yield PhSNHMe and McaNNHMe respectively. 

For the formation of 45, nitrobenzene would be reduced to aniline by CO/H2O (see Chapter 4.2.). By aldol condensation, an a,p-unsaturated aldehyde is formed. Michael addition of aniline to the unsaturated aldehyde followed by ring closure with dehydration would form 1,2-dihydroquinoline. Oxidation of this last product by nitrobenzene would yield 45. This sequence of reactions is similar to what proposed in Scheme 15. For the formation of 46, an intermediate nitrene was suggested (Scheme 16). Addition of the nitrene to the aldehyde would give an oxaziridine and, correspondingly, an isomeric nitrone. The nitrone would then be reduced by CO to the Schiff base and this, in turn, would be reduced to the amine. Final reaction with one more molecule of aldehyde would lead to 46. Some previously made comments on the formation of Schiff bases from nitroarenes and aldehydes vide supra and Chapter 4.5.) also apply to the first part of this scheme. 

Singlet phenylnitrene, and hence /V,A -diethyl-3//-azcpin-2-amines, e. g. 102, can be generated by the thermolysis of A,-phenyl-Af,<9-bis(trimcthylsi]yl)hydroxylamine (100) in the presence of dialkylamines the reaction fails, however, with arylamines.210 Photofragmentation of the spiro oxaziridine 101 in diethylamine solution also produces the 3//-azepine 102,2,1 and an oxaziridine intermediate is probably involved in the formation, in low yield (1 %), of azepine 102 by the photolysis of A/,A( -diarylbenzoquinonc diimine A/,A/ -dioxides in benzene/die-thylamine solution.212... 

The vast majority of organocatalytic reactions proceeds via covalent formation of the catalyst-substrate adduct to form an activated complex. Amine-based reactions are typical examples, in which amino acids, peptides, alkaloids and synthetic nitrogen-containing molecules are used as chiral catalysts. The main body of reactions includes reactions of the so-called generalized enamine cycle and charge accelerated reactions via the formation of iminium intermediates (see Chapters 2 and 3). Also, Morita-Baylis-Hillman reactions (see Chapter 5), carbene-mediated reactions (see Chapter 9), as well as asymmetric ylide reactions including epoxidation, cyclopropanation, and aziridination (see Chapter 10), and oxidation with the in situ generation of chiral dioxirane or oxaziridine catalysts (see Chapter 12), are typical examples. 

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