Reactions with aziridines, 53. — Arene hydrides, 9. intermediate substitution in the formation of a benzylic anion by an aromatic radical anion as observed with 1‐benzoyl‐2‐phenylaziridine

Abstract

The reaction of the title compound 1 with anthracene hydride AH‐ or anthracenide A‐' leads to the formation of the ben‐ zylic anion 9 by fragmentation of the first generated substi‐ tution intermediate 7 or 8. In the reactions with AH‐ the carb‐ anion 9 is completely trapped by protonation with dihydroan‐ thracene AH2 yielding the reduction product 3 (N‐benzoyl‐phenethylamine).phenethylamine). In reactions with A‐' as well as with naph‐ thalenide N‐' the carbanion 9 either abstracts a proton from the solvent THF (yielding 3) or adds to the benzoyl group of unreacted 1 which finally results in P‐benzamido‐ct‐phenyl‐ propiophenone (6).

Benzylic Fragmentation (BFR), an Aromatic Analogue of E1cB Including a Homolytic Variant, as either Nucleofugal or Homolytic Path to Aryl Stabilized Carbanions or Ketyls, respectively

“…Yields of 23a -d reported (67 -82% for 23a,b,d) in this paper may be a bit low due to lacking knowledge on the importance of excess AH¯ and other mechanistic details. This holds in particular for aziridine 17c that was later [7] shown to yield 99% of 23c (= 16 in Scheme 3) from reaction with AH¯Na + . This yield certainly includes a contribution by BFR 14 → 15 of Scheme 3 since some 14 must arise from coupling of radical 21c with A ·¯ generated by BFR.…”

“…This short lifetime makes the behaviour of benzylic halides towards A ·¯ mechanistically deviate from that one of alkylhalides [23] in a manner that previously could not be explained. It was shown 1990 [7] and suspected already before that BFR was the reason why no benzylated dihydroanthracenes could be detected as products: intermediate 14 (Scheme 3) can be detected by isolation of 13 (25%) when in the reaction of A ·¯N a + with aziridine 17c (Scheme 4) the reaction time including the time for addition of 17c does 15 seconds not exceed [7]. Within 1 minute this yield drops to 13% and goes afterwards to zero.…”

“…__________________________________________________________________________________ PROGRESS REPORT 5 min reaction of 11 with excess AH¯Li + provides 13 and 16 [7]. The yields of this single run are not at all optimized but no eliminative decomposition of 15 was observed.…”

Nucleophilic ring opening of aziridines

“…An essential reaction of AHwith benzoyl-Az's is the special inner-sphere SET followed by homolytic ring opening of 80 and, in part, by coupling (pseudo RNO) to give 115 [70]. Isolation of products 115 requires always special care [53a] since 115 undergo benzylic fragmentation BFR in the reaction mixture (Scheme 21) with sufficient time and excess of AH - [70]. BFR can be slowed both sterically and by counter ion Li + .…”

Amidoethylation of Anthracene Hydride by N-Aroylaziridines: Inner-sphere Single Electron Transfer (SET) and Radical Coupling confirmed

“…When the aziridine ring of 1a carries substituents, analogues of 7 are obtained 3 unless they arise from 2-phenylaziridines and are unstable under usual conditions. 3,5 The assumption 3 that 7 and its analogues are formed by coupling of amidatoalkyl radicals with anthracenide A À was supported by a regioselectivity of ring opening that seemed to exclude a direct S N 2-like path to analogues of 7 and hence also to 7. Subsequently it was found 6 from a study of 1-acyl-2,2-dimethylaziridines that S N 2-like ring opening may require planarization of the nitrogen pyramid thereby shifting the mechanism to a borderline type whose regioselectivity is compatible with the AH À results.…”