98943-92-1Relevant academic research and scientific papers
Reactions of Carbanions with two Sterically Demanding 1-Benzoylaziridines: SET, SN2, Carbonyl Attack.
Bellos, Konstantinos,Stamm, Helmut
, p. 269 - 273 (2007/10/02)
Reactions of 2-phenyl (1a) and 2-benzyl (1b) 1-benzoyl-2-butylaziridines with carbanions X-, AH-, and Fl- of xanthene, dihydroanthracene and fluorene always form N-(2-butylethyl)-benzamides carrying phenyl (9a) or benzyl (9b).This reductive ring opening indicates an SET mechanism with aziridino ketyls 6a,b as intermediates.Nucleophilic ring opening (SNs) is found only with the carbanion of the lowest reducing power: Fl- 5a,b (62percent, 14percent).These two mechanisms cleave different bonds, a finding without precedence in SN2/SET competitions.Carbonyl addition resulting in benzoyl transfer to xanthene, dihydroanthracene or fluorene is usually also observed.It is the main reaction with X- and 1a.The highest yields of 9a,b are obtained with AH- since a special inner-sphere SET is available.
Single Electron Transfer versus Nucleophilic Ring Opening in Reactions of Cis-Trans Pairs of Activated 2-Phenylaziridines. Strong Influence of Nitrogen Pyramid for N-Benzoylaziridines
Falkenstein, Reinhard,Mall, Thomas,Speth, Dieter,Stamm, Helmut
, p. 7377 - 7381 (2007/10/02)
Activated 2-phenylaziridines with a second substituent R in position 3 were made to react with xanthyl anion X(1-).Nucleophilic ring opening is the only reaction that occurs with sulfonyl activation.The analogous N-benzoylaziridines 1 undergo this type of ring opening when the two substituents Ph and R are trans.The cis isomers (cis-1, Ph and R cis) react in this manner to a negligible extent if any.The (nearly) exclusive ring cleavage reaction of cis-1 is C-N homolysis of an intermediate ketyl formed by single electron transfer (SET) from X(1-).This cis-trans phenomenon is in accordance with the hypothesis that the two competing reactions depend in an opposite manner on the steepness of the nitrogen pyramid.A predominant or exclusive final result of SET is reductive aziridine opening and dimerization of the xanthyl radical X(.).Formation of both diastereomers of the amidoethylated xanthene in one case (R = Me) is evidence for a cross combination of X(.) with the radical formed by homolytic ring opening.Cross combination is also a likely path for R = H (no cis-trans isomerism), in addition to reductive ring opening. cis-Aziridines with dimethylcarbamoyl on nitrogen do not react via SET since the ketyl is not stabilized and therefore difficult to generate.Carbonyl attack on both types of acylaziridines competes more or less successfully with the two ring cleavage reactions.
Regioselectivity in Nucleophilic Ring Opening of 2-Methylaziridines. Lag of Bond Making as Model for the Abnormal Opening
Lin, Pen-Yuan,Bentz, Gunther,Stamm, Helmut
, p. 23 - 34 (2007/10/02)
The regioselectivity ratio RS=normal:abnormal opening of activated 2-methylaziridines 2 by nucleophiles is found to range from 0.10 to unmeasurable large (only normal opening=substitution at CH2 by strongly basic carbanions).RS is assumed to result from SN2 variants differing in the degree to which bond breaking is ahead of bond making including perhaps synchronous SN2.Bond breaking will be more ahead for the N-CMe bond.High nucleophilic power pushes bond making toward a synchronous process resulting in great RS.The decrease in RS with acyl activation relative to sulfonyl activation is in accord with a flattening of the nitrogen pyramid (planarization effect).The planarization effect is retained in acidic medium by O-protonation: RS 0.10-0.14 for methanolysis as compared to RS 0.43 for N-protonated sulfonylaziridine 2h.AM1 calculations support the planarization hypothesis. - No indication for SET with trityl anion was found.
Reductive Ring Opening of N-Benzoylaziridine by Anthracene Hydride (Anion of 9,10-Dihydroanthracene) via Base-Induced Fragmentation of the Intermediate Carbonyl Adduct
Stamm, Helmut,Mall, Thomas,Falkenstein, Reinhard,Werry, Juergen,Speth, Dieter
, p. 1603 - 1607 (2007/10/02)
As previously reported reaction of anthracene hydride (AH-) or of its oxa analogue xanthenyl anion (X-), with N-benzoylaziridines 1a,b can result in amidoethylation (2a,b and 3a,b) of the carboanion, in reductive opening (4a,b) of the aziridine ring, and in attack on the carbonyl group of 1a,b.We now show with 1a that both the rate of ring opening and the amount of reductive opening are significantly enhanced by an excess of AH-Li+ while the initially formed (90percent) carbonyl adduct 6a survives with a defict of AH-Li+.Both effects due to carbanion excess are absent with X-Li+ but are much stronger with AH-Na+.These results point to a rapid process that is triggered off by deprotonation at position 10 of the carbonyl adduct 6.A concerted or subsequent homolytic fragmentation is proposed to generate the ketyl 5 of 1, followed by homolytic ring opening of 5 to yield the radical 12, which is reduced to the carbanion 14.The latter forms 4 by capturing a proton from dihydroantracene.Inaccessibility of reductive ring opening for a trialkylacetyl-activated aziridine is demonstrated again (18).
Reactions with Aziridines, 45. - Arene Hydrides, 5 Reversibility of Carbonyl Attack on N-Benzoylaziridines Prior to Ring Opening by Carbanions. - Strong Influence of the Gegen Ion
Mall, Thomas,Stamm, Helmut
, p. 1349 - 1352 (2007/10/02)
A previous report had shown that anthracene hydride AH- or the xanthenyl anion X-, respectively, at first add to the carbonyl group of N-benzoylaziridines since high yields of benzoyl dihydroanthracene 3 or benzoyl xanthene 11 were obtained when in early stages the reaction was quenched with protons.The respective intermediate carbonyl adducts 2 and 10 had been considered to be precursors of products resulting from homolysis of the aziridine ring.It is now shown that quenching of the reaction between AH- or X- and N-benzoylaziridines 1a, b with methyl iodide or aroyl chlorides results in substantial yields of products derived from either AH- (or X-) or 1a,b.This indicates that 2 (or 10) are in equilibrium with AH- (or X-) and 1a, b.Study of the gegen ion influence with X- revealed that the equilibrium concentrations of 10-Na+ were much lower than those of 10-Li+ while simultaneously the ring opening of 1a was distinctly faster with X-Na+ than with X-Li+.This finding suggests that, contrary to the previous assumption, the equilibrium concentrations, of X- and 1a are responsibile for the (homolytic) ring opening.
